HomeMy WebLinkAboutAPA3099SUSITNA
TABLE OF CONTENTS
Acknowledgments
Preface
of Tables
0f Figures
INTRODUCTION
GEOMORPHOLOGY OF THE SUSITNA RIVER . . . .
2.1 Middle River .... ~ . o •• ~ •
2.1.1 Geomorphic History and Processes
2.1.2 Effects of River Ice
2.1.3 Sediments ..... .
2.2 Lower River ............... .
2.2.1 Geomorphic Processes
2.2.2 Effects of River Ice
2.2.3 Sediments .•...
3. VEGETATION BACKGROUND
4.
5.
3.1 Vegetation Succession
3.2 Seed dispersal and Germination
3.3 Flooding Effects
METHODS . • . . .
4.1 1981 Methods
4.2 1984 Methods
VEGETATION DESCRIPTIONS AND SITE HISTORIES
5.1 Early Successional Stages
5.1.1 General Descriptions ... .
5.1.1.1 Horsetail ... .
5.1.1.2 Juvenile Balsam Poplar
5.1.1.3 Willow ... .
5.1.1.4 Others .... .
5.1.2 Site Histories
5.1.2.1 Site 8 .•....
5.1.2.2 Site 13
5.1 .. 2 .. 3 Site 1
5.1.2.4 Sites 14, 15, 16 ...... ~ .
5.1.2.5 Site 5 ....
5.1~2.6 Site 20 9 •••
5.1.2.7 Site 21 ........... .
5.1.2.8 Site 25 ... .
5.1.2.9 Site 22 ... .
5.1.2.10 Site 18
ii
iii
vi
1
4
4
L~
6
7
8
8
10
11
13
13
16
18
20
20
23
26
26
26
27
28
28
28
30
30
31
32
34
36
36
37
37
39
40
6.
7.
5 ..
5 .. 3
Successional Stages
Descriptions . .. e o
Se2o2 Site Histories . ~ . ~
5.2e2.1 Alder •• c • $
5.2.2.1.1 Site 27
5.2.2.1.2 Site 23
5.2.2.1$3 Site 2
5.2.2.1.4 Site 19
5.2.2o2 Immature Balsam Poplar
5.2.2.2.1 Site 20
5.2.2.2.2 Site 26
502.2.2.3 Site 12
Late Successional Stages
5.391 General Descriptions
5.3.2 Site Histories .•••
5.3.2.1 Mature and Decadent Balsam Poplar
5.3.2.1.1 Site 3 . • • . . $ ••
5.3.2.1.2 Site 24 ...•
5.3.2.1.3 Site 17 •••.
5.3.2.1.4 Site 28 ••••
5.3.2.1.5 Site 31 ••••
5.3.2.2 Paper Birch -White Spruce
5.3.2.2.1 Site 29
5.3.2.2.2 Site 11
5.3.2.2.3 Site 4
CONCEPTUAL MODEL • • • •
6.1 General Description .••.
6.2 Early Successional Stages ..•.
6.2.1 Colonization and Seed Dispersal
6.2.2 Establishment .•..•.•.••.
6.2e3 Ice Effects •.•..... ~ o •.
6.2.4 Substrate Erosion and Deposition
6.2.5 Winter Ice Cover •••.. ~ o o ••
6.3 Intermediate Successional Stages
6e4 Late Successional Stages
PROJECT EFFECTS
7e1 Geomorphology
7.2
7.3
7.1.1 Middle River
7el.2 Lower River
Vegetation ~ . . .
Potential Mitigation Measures
8. SELECTED BIBLIOGRAPHY ••••..••
49
51
51
53
53
56
56
59
60
.. 6., ..
64
66
67
67
69
70
72
72
73
73
77
80
81
82
92
85
89
89
89
90
91
94
96
SUMMARY
River is a river in &outhcentral
ric project has been proposed.. Vegetation
summer floods and ice scour during breakup$
is associated with normal s11Inmer water levels in a
ice iams repeatedly occur.. Shrub-sized vegetation is an
resource for moose forage, and is found predominantly in
stages of vegetation. There is concern about
in water levels as a result of project operation would
and moose browse in particular~ These studies were intended
an understanding of the existing riparian dynamics and to
occur with the project in operation.
earliest stages of vegetation were dominated by horsetail (--~----
-.-~~.~-', balsam poplar (Populus balE"amifera), and feltleaf -v·illow
and generally occurred 5 to 15 years after island
were good sources for browse, but many stems were too short to
above winter snow. Intermediate stages included sites dominated
(Alnus tenuifolia) and immature balsam poplar. Sampled sites had
little bro~~ but sometimes willow in narrow strips of alder
might be important for browse production. Alder would dominate the
ve ge ta ti on from 25 to 45 years after island stabilization while balsam
poplar would dominate for 55 to 85 years afterward.. Mature and decadent
balsam poplar communities of later successional stages had the most available
browse by twig count because of the well-developed shrub understory and open
overstoryo It dominated from 100 to 150 years. Similarly paper birch
(Betula papyrifera) -white spruce (Picea glauca) types contained
considerable bro~se and dominate after 180 to 200 years.
Lower summer flows with the project would make new land surface
available for colonization by plants in summer provided soil moisture and
texture were suitable.. The lower water levels may delay vegetation
colonization because moisture is critical during spring germination. Higher
winter levels with ice staging would flood newly established vegetation,
preventing colonization by anything except annuals. Areas above the ice
front would not be subject to this, but the coarse substrate and low summer
water levels may slow colonization. Further development of existing
vegetation would probably not be hampered unless the lower water tables had
an effect on species composition.
work with this was
and Experiment
1981 studi~s were funded by the
on a subcontract to the Terrestrial Environmental
to Acres American, the prime contractor
The 1984 field studies were funded by the range
to support part of the writing and data analysis were provided
a to Harza-Ebasco Susitna Joint Venture, the current
contractor for the Susitna Hydroelectric Project.
would like to express extreme thanks to Beth Cape, our typist,
many hours spent producing this and previous versions. Also, a special
thanks to Dr. Jay McKendrick for reviewing the Conceptual Model Sectiono
We would also like to thank our Zenith 100 for making this possible and
not breaking down too oiten.
Most of Tables 3-30 and some of the successional sequence descriptions
were modified from McKendrick et al. (1982).
the second
sections an
effects of the Susitna
Project Effects. The other sections contain
pressed for time can probably what
, referring to earlier sections as needed
background. The Site Histories sections contain a lot of
information on changes at or near our sites and are to
we arrived at our understanding of vegetation succession
River. Readers only interested in a synopsis can probably
contributing to this paper were:
Vegetation:
Wildlife:
Geomorphology:
Dot Helm
William B. Collins
Joseph C. LaBelle
AFES
AFES
AEIDC
4.
5
7.
8 ..
9 ..
11.,
12 ..
13.
14.
15.
LIST OF TABLES
River Reach Definitions
Bed Material 1
Percent cover on ear 1 y s uc ce ssional stands on downstream 105
floodplain of Susitna River, summer 1981.
nsity (stems/ha) of woody species in early vegetation
successional stages on downstream floodplain of Susitna River,
summer 1981.
Characteristics of \voody species in early vegetation
succession stands on downstream floodplain of Susitna River,
summer 1981.
Density and twig count means by successional stage for browse
species. All numbers have been rounded.
Percent cover for stands dominated by horsetail on downstream
floodplain of Susitna River, summer 1981.
Characteristics of woody species in stands dominated by
horsetail on downstream floodplain of Susi tna River, summer
1981.
Density (stems/ha) of woody species in stands dominated by
horsetail on downstream floodplain of Susi tna River, summer
1981.
Percent cover for stands dominated by juvenile balsam poplar
on downstream floodplain of Susitna River, summer 1981.
Characteristics of woody specie~; in stands dominated by
juvenile balsam poplar on downstream floodplain of Susi tna
River, summer 1981.
Density (stems/ha) of woody species in stands dominated by
juvenile balsam poplar on downstream floodplain of Susi tna
River, summer 19810
Percent cover for stands dominated by feltleaf willow on
downstream floodplain of Susitna River, summer 1981.
Characteristics of woody species in stands dominated by
fe 1 t leaf willow on downstream flood plain of Susi tna River,
summer 1981.
Density (stems/ha) of woody species in stands dominated by
felt leaf willow on downstream floodplain of Susitna River,
summer 1981~
106
107
108
109
110
112
113
114
115
116
117
118
20~
21
23 ..
25~
26.
27 ..
29 ..
30.
31 ..
cover in stands on downstream
, smnmer 1981 c
(stems/ha) of woody species in alder stands on 1
floodplain of Susitna River, summer 198lo
Characteristics of trees and tall shrubs in alder stands on 121
downstream floodplain o: Susitna River~ summer 1981~
cover in immature balsam poplar stands on downstream 1
floodplain, summer 1981.,
Density (stems/ha) of woody species in immature balsam poplar
stands on downstream floodplain, summer 1981.
Characteristics of woody species in immature balsam poplar
stands on downstream floodplain of Susitna River, summer
1981 ..
123
124
Characteristics of trees and tall shrubs in immature balsam 125
poplar stands on downstream floodplain of Susitna River,
summer 1981.
Percent cover in mature and decadent balsam poplar stands on
downstream floodplain, summer 1981.
Characteristics of woody species in mature and decadent balsam
poplar stands on downstream floodplain of Susitna River,
summer 1981.
Density (stems/ha) of woody species in mature and decadent
balsam poplar stands on downstream floodplain, summer 1981 ~
Characteristics of trees and tall shrubs in mature and
decadent balsam poplar stands on downstream floodplain of
Susitna River, summer 1981.
Percent cover in birch-spruce stands on downstream floodplain,
summer 1981e
Characteristics of trees and tall shrubs in birch-spruce
stands on downstream floodplain of Susitna River, summer 1981.
Density (stems/ha) of woody species in birch-spru~e stands on
downstream floodplain, summer 1981.
Characteristics of woody species in birch-·spruce stands on
downstream floodplain of Susitna River, summer 1981.
With-project morphological changeso
126
127
128
129
130
131
132
133
134
OF
region.
11, 12, 13o
3 sites 12, 13, 14, 15, 16, 17o
of sites 18, 2G ..
of 18' 19"
of sites 25, 26.
Locations of sites 27, 28o
8 .. Locations of sites 4, 5, 6, 7, 8, 9, 10~
90 Locations of sites 1, 2, 3, 31$
11.,
12 ..
13 ..
14 ..
15.,
16.
17 ..
18 ..
Locations of sites 22, 23, 24, 29.
Feltleaf willow plant which has been buried and regrown@
Balsam poplar plant which has been buried and regrown.
Horsetail site 8 in 1981 (left) and 1984 (right).
Horsetail willow site 13 in 1981 (left) and 1984 (right).
Time line indicating vegetation types and major events during
succession along the Susitna River.
Young willows that have been scraped by ice, site 12, 1981.
Young willows that have been pushed with the soil berm by ice,
site 12, 1981 ..
Diagram of conceptual model of vegetation succession along the
Susitna River ..
1
1
l
1
141
142
1
145
146
147
148
149
150
151
152
153
Natural and with-project flows and their implications for 154
vegetation establishment.
of land. The river
Alaska Range, on the east by the
lowland, and on the south by Cook Inletc
Chulitna, Talkeetna, and Yentna
proposed Susitna Hydroelectric
at Watana and later at Devil Canyono
(
o j ec t wi 11 i nc
floodplain along the Susitna River below the dam sites
na c vegetation relationships. Vegetation is important r
dams
stabilization and wildlife habitat, especially moose browse production~ The
existing river dynamics are responsible for maintaining vegetation in y
stages or eliminating older sites and providing new areas
colonization by plant species.
Peak discharges frequently occur in May and June under natural
conditions, but average water levels are usually higher in July and August
during the summer rains.. High spring water levels frequently occur when
seeds of early successional species, such as balsam poplar (PoJ2u.lus
balsamifera) and feltleaf willow (Salix alaxensis) are being dispersed. The
lowest water levels occur in September, October, and November before ice-
related staging raises water levels to near summer conditions. This cycling
of water levels allows seeds to be deposited in the spring, the only time
when these seeds are viable, and to grow if there are 110 significant floods
later in the summer. Vegetation may not colonize each year if conditions are
not suitable for seed dispersal, germination~ and plant establishment.
Other means of dispersal could also account for some establishment. The key
factor in plant establishment appears to be high water during spring
3
river;
the confluence to
Susitna River Hydroelectric
river, most of the following
lower river ..
's
no
concentrate on
2
water
moisture
-::tnts in
and insulating snow cover are
water levels with the project in
are now (10,000 Gold Creek with versus
under natural conditions) and higher under cover
water levels corresponding to (30,000 cfs versus 20,000 s
0
water) (Harza-Ebasco 1984c, 1985). Flooding will tnundate esta d
in some places, causing it to be ice-covered for up to 4
winter$ Flooding and ice jamming effects which give the system a pulse
to set back vegetation succession under natural conditions will be
by regulation.. Ice jamming effects will be almost nonexistent in
middle river because ice will melt out in place rather than through a
forceful breakup.
Concern exists ahout the effect of changes in river flow and lee
regimes on the vegetation and moose browse. Will the new areas available
colonization be vegetated? Will vegetation advance uninterrupted and reduce
the amount of moose browse? Will vegetation succession be set back
occasionally to increase moose browse? To be able to predict what might
happen with the project, one must understand the existing system and what
makes it work. Understanding plant ecology, including the effects of river
hydrology, is necessary for interpretation of the existing systemQ Only then
can reasonable projections be made of the project impact.
For simplicity of discussion, the Susitna River will be divided into
three zones .. The upper river is considered to extend from the Susitna
3
, most on
turns abt'uptly
a
99 miles to Cook
2 River
4
the
runs in a souther 1 y
near the
for about 135
The flows
2.1 Geomorphic History and Processes
ver con£ ce
to
the Pleistocene ice age, the Susitna valley was th
e that extended all the way into Cook Inlet. When the
at the of the Pleistocene about 10,000 years
to cut down through the glacially-eroded bedrock surface in
basin, eventually cutting canyons several hundred feet deep in
river reach. Today the middle river flows through the canyon
on a riverbed characterized by single-channel and split-channel
( Tc: 1).
the :river cut, or degraded, way into the canyons, the active
floodplain elevation slo\vly dropped below old riverbed Some older
are evidenced today by the presence extensive sedimentary terraces
perched above both sides the river. These old terraces are sometimes high
uove the river, are generally covered by old forests, and they are not
affected by river processes such as flooding. Some terraces are, however
5
events
terraces ..
e midd river slowly underwent de ad of its
u~~Au~s years, and studies show that it appears to have
. om 1949 to the present (AEIDC 1985) .. Although new
, and change shape through sediment redistribution, many
emerge and become more and more exposed at the surface as
degrades. Eventually, some bars rise high enough above the
they are seldom affected by flooding or ice processes, and
s
stabilized islands with mature vegetation" Many emergent gravel bars
have become attached to the riverbanks and are now forested terraces at
various elevations above the modern river floodplain ..
Most of the river's flow is carried by the mainstem channel, which
deepest channel or "thalweg". Mainstem waters are turbid in summer,
to high concentrations of suspended glacial silts. In winter,
waters are generally clear because glacial melt ceases. Side channels and
sloughs are overflow channels. Water flows into them from the mainstem only
during high flow periods or during ice staging, when flows are high enough to
overtop intervening gravel berms~ At the mouths of sloughs, backwater
effects from the mainstem always contribute to slough water flow. In sloughs
and some side channels, water also flows from mainstem-influenced ground
water upwelling, other springs and seeps, and side slope brooks and rivulets
(Bredtl1auer and Drage 1984a) .. All of these waters are clear ..
As the river degrades and gravel bars emerge, side channels that once
ran behind some gravel bars also emerge and become "perched". In this way,
many side channels evolve into side sloughs, and side sloughs evolve into
.. 1 2
6
Some
no carry water any circumstances,
Old channels of this type are found on many the
and terraces ..
of River Ice
out 7 months of each year, ice dominates the
during freezeup, dynamically changing during mi
ally flushing out of the system during breakup ..
nter 9 and
Some of
of ice formation and decay have a permanent ef feet on ver
morphology, vegetation, and fish and wildlife habitats.
Although river flows and geomorphic regime (the balance of aggradation
and degradation over time) are major factors controlling channel evaluation,
processes also appear to influence river morphology in the middle
zone. For example, formation and alteration of some sloughs may be related
to breakup ice jams, and riparian vegetation may be bent and scraped by
scouro
Some of the sloughs may have been formed when breakup ice jams caused
the river to stage upstream of the jams. This process was observed to
occur in 1976 at Slough 11 near Gold Creek (R&M Consultants, Inc. 1984a).
At this site an upland slough was changed to a side slough .. Floods
overtopped the river banks and flowed through depressions in a terrace. Ice
blocks carried in by the floods eroded away the terrace materials,
substantially lowered the elevations of the entrance berm, and th4n deepened
and enlarged a slough channelo
er s a on s i
along
by the height to which ice
in locations where jams frequently occur.,
of vegetated islands is sometim~s
frequently subjected to ice jams have
trees not only adjacent to cut banks but also further in
stand. Some stands of young trees that occupy the upper ends
second generation growth after a major ice jam event broke tree
at ground level in an earlier stand (R&M Consultants, Inca 1984a)c
2 .. 1.3 Sediments
mature
Bed materials of the Susi tna River are composed principally of gravel
cobbles, ·11ith a minor amount of sand. The medL_;.n, size of sediments
the mainstem is somewhat larger than those in side channels, and sediment
sizes along riverbanks are somewhat larger than those in channels., Bed
material size distribution in the middle river is shown in Ta e 2
(Harza-Ebasco Susitna Joint Venture 1984a). Most of the middle ver
main stem bed is composed of medium to large gravel, cobbles, and boulders
until reaching the vicinity of the Susitna-Chulitna rivers confluence, where
the riverbed sediments abruptly become smaller and more transportable as a
result of inputs from the Chulitna.
Compared to the lower river, which is largely influenced by the Chulitna
River, the middle Susi tna River carries rela ti vel y 1 it tl e tr an sp or table
bedload. Principal contributions of sediment to the middle river are from
glacial sediments from upriver, talus slopes, mass wasting, erosion of river
from streams ( &
s t, coming om the P.-"ciers and from run is
in middle river, especia~ly during high flow eventso
is deposited in backwater and low-velocity zones
breakup~ These sediments are then redistributed
summer floods (R & M Consultants, Inc .. :984a) .. Silts are
during breakup at the upper ends of ice jams where staging occurs
and water velocity slows, allowing finer sediments to deposit on
, islands, and low terraces, and some silt is deposited directly
ice blocks ..
Some slough channels are overlain with fine sands and silts during
events .. These fine sediments are then removed during high-flow
events, such as summer floods.
2 .. 2 Lower River
2o2ol Geomorphic Processes
The lower river flows over a thick deposit of sediments laid down over
thousands of years by the Susitna and Chulitna rivers and their tributarieso
Near the Susitna-Chulitna confluence, the Susitna River changes abruptly
to a braided and multiple channel pattern for the remainder of its length.
the Delta Islands area from about RM 61 to 42, the river has a combined
pattern, vJith a braided pattern on the west side of the islands, and a
multi-channel pattern on the east sidee A summary of river patterns in the
lower river is presented in Table 1 (R & M Consultants, Inco 1982)e
9
to to a
(R & M e 1982):
1. Abundant sediment load and high
2o Large and sudden discharge variations;
3. High gradients;
4. Low channel stability;
So Erodible banks.
rates;
All of these factors are present in the Chulitna River ..
seems to be dominated by the braiding patterns developed in the
Chul na River .. The regime of the river below the Susitna
confluence suggests that the middle Susitna River is morpholog~.ca Y a
tributary of the Chulitna River rather than the other way around as is
usually considered.
Large braided rivers like the Susitna have wide channels, rapid shifting
of bed materials, and continuous shifting of the position of the ver
course., The amount of channel shifting varies with flow fluctuations
(Leopold et al. 1964).
The Chulitna River has an abundant sediment supply from a number of
large glaciers in the nearby Alaska Range. Consequently, the lower river is
much nearer to that sediment source than to the distant glacial sources in
the upper Susitna River.
Channel pattern in the lower river are quite dynamic, and river
morphology here is related primarily to summer high-flow events .. When
summer disharges overtop gravel berms between the mainstem and side channels,
bed material is set in motion, often resulting in changes in channel network
configuration and shape (R & M Consultants, Ince 1982).
10
are usually
usually results a decline in def.osi ted e
reflecting a down-bar decline stream (
morphology often changes systematically m, however "
Ashley (1975) found that, on the Yana outwash near
Glacier, bars changed in a downstream direction from coarse-gravel
bars with low bed relief to finer gravel longitudinal bars
higher bed relief, and then to a combination of sandy longitudinal
lingoid bars ..
2o2.2 Effects of River Ice
lo\ver river has a broad, active floodplain exceeding a mile in
River staging due to freeze-up can spread over a wide area and,
consequently, does not rise very high. No significant overbank flooding
takes place ..
Several side channels are commonly flooded, but few side sloughs are
overtopped, and when they do it is with little flow and carrying little or no
ieee The ice cover below Talkeetna is usually confined to the thalweg
channel, which usually occupies less than 20 percent of the floodplain
width (R&M Consultants, Inc. 1984a)~
Breakup is generally quite gentle, with no dramatic ice drive0 At most
a few small ice jams occur at the lower ends of open leads as the ice cover
melts away in the early stages of breakup .. The lower river is usually
nearly melted out before the breakup drive from the middle river occurs, so
occur
river to Cook
3
.a and Talkeetna rivers contribute
~oad to the lower Susitna Rivere Bed materials
are finer than those the middle rivers
sizes are extremely varied in preglacial aided vers,
from silt-clay low-energy deposits, such as those found in
and overbank deposits, to high-energy gravels on active river bars
and in migrating channels.
Sediment sizes generally become smaller downstream, and the sorting of
sediment sizes improves. At tte Susitna-Chulitna confluence, coarse gravel
Downstream the materials become finer. Near Talkeetna,
materials are composed of 70 percent cobbles and 30 percent gravel. At
Sunshine, where the Parks Highway bridge crosses the lower river, the bed
rna terials are composed of 29 percent cobbles, 66 percent gravel , and 5
percent sand (Harza-Ebasco Susitna Joint Venture 1984).. Nearer the
mouth, sand dominates the composition of many river bars.
Once a river bar emerges above the surf~ce of the water it may become
stabilized by vegetation. This helps prevent the island thus formed from
being easily eroded and also tends to trap fine sediments during flooding
or eolian deposition. In this manner many bars become coated with a veneer
of silt (Leopold et al. 1964).
A large proportion of total annual bedload transport takes place during
the short periods of summer flooding. During summer high-flow events, large
2
are
continuouslyo , on a
to be in equilibrium (Harza-Ebasco )
13
have reported on vegetation development rivers
and arctic imatic zoneso Succession on
along Colville River near Umiat, Alaska, other
Alaska were studied by Bliss and Cantlon (1957)@ Several species
legumes, and other forbs became established on sands and
on top of gravel. Most feltleaf willow (Salix alaxensis) came
banks that had caved in, and few seedlings were observed@
successional areas graded into those dominated by young and
felt leaf willow, which may be 10 em in diameter and be 46
olde These are much larger willows than what we normally find on the Susitna
(McKendrick et al .. 1982).. More feltleaf willow was found on gravelly
alluvium than on sandy or silty materials (Bliss and Cantlon 1957) in
contrast with Susitna,. Communities dominated by alder (Alnus
shrub-dwarf heath meadow occurred on terraces, sharply separated from the
early stages ..
Viereck (1970) described vegetation and soils from four different
successional stages along the Chen a River near Fairbanks , Alaska .. The
earliest stage sampled was a 15-year old feltleaf willow stand, ~ominated by
herbs and shrubs with light weight seeds" Balsam poplar (Populus balsam-
ifera) was generally established at the same time, but its growth was
slower.. After balsam poplar grew taller than the willow, rose (Rosa
acicularis) and high bush cranberry (Viburnum edule) became important in the
understory, similar to what occurs along the Susitna. Willow was established
on soils with particles greater than 2 mm in size consti tutin; 5% of the
1
finer textures ere w w ows ong e si tna
et \ I ..
Chena River balsam poplar dominated canopy in
50 years old, then white spruce <~--
1 years after stabilization (Viereck 1970).
on the Susitna were over 100 years old, and white was
important in the understory, although the time frame for e
ruce establishment was very variable (McKendrick et al@ 1982) G
stan white and black spruce (Picea mariana) dominated 220 old
stands along the Chena (Viereck 1970) while paper birch (Betula
spruce dominated 200-year old stands along the Susi tna (McKendrick
et al .. 1982) 0 Mature sites along the Chena River were under by
permafrost (Viereck 1970), which was not present on the Susitna.
Dyrness et al. (1984) reported on succession along the Tanana River near
Fairbanks in interior Alaska, with results somewhat similar to Viereck's
( 1970) results for the Chena River.. Silt bars were colonized by several
species of willow, alder, and balsam poplar, with the first two species
dominating for 15 to 2 0 years. Poplar then grew taller than them and
domina ted for the next 60 to 80 years. White spruce so me times invaded
rapidly or became established over a period of years, but eventually it grew
taller than the poplar.. The establishment of white s pr uc e depended on
periodicity of the seed crop, distance to seed source, floods, silt
deposition, and other factors affecting seed dispersal, germi nation , and
establishment.. Black spruce eventually dominated o This sequence closely
1
) reported a
River in British Columbia. They white
occurred, but did not , on
agree with our data where spruce are older and at an
of succession rather than at a later stage Q Spruce
required mineral soil and some shade. Three generations
might occur before black spruce dominated.. Nan son and
( ) also observed that the poplar to spruce transition occurred relatively
with no mi-ed stage.. This was similar to our observations
poplar-spruce stands were relatively rare compared to mature poplar or
spruce alone ..
Craighead et al. (1984) have briefly studied vegetation succession along
the Stikine River in southeast Alaska to assess the impact of a hydroelectric
project oa moose browse in the downstream reacheso Newly exposed riverbanks
were colonized by several species of horsetail (Eguisetu!!!, variegat~,
Eo arvense, E .. fluviatile) and willow (Salix alaxensis, ~ .. interior).. Other
willow species entered later. Feltleaf willow became less important as alder
( rubra) and black cottonwood (Populus balsamifera ssp .. trichocar:e~)
became more iffiportant.
Gill (1972) used vegetation to categorize certain alluvial environments
in the Mackenzie River delta since different vegetation reflected fluvial and
aeolian sedimentation processes. Fine sands were more important at upstream
ends of point bars while silts were more important at the downstream ends.
This was attributed, at least in part, to helicoidal flows causing shifting
1
warmer soils root
were by permafrost or water sam po
forbs were important early
was an important shrub than 1 .. 6 m
in the layer up to 6 m tall. Feltleaf willow was
most common willow on the Susitna River, but it was y 2 m
( et al .. 1982).
Sigafoos (1964) extensively studied flood history along portions
River near Washington, D .. C.,, based on evidence from trees ..
establishment and maturation of trees resulted from interrelated sequence in
timing of seed dissemination and germination, sui table en vi ro nmen ta 1
conditions, and flow regime of the river. Flood history could be determined
from buried tree rings since new wood formed on a buried trunk is more
root wood than stem wood. All trees could withstand 1 m of sedimentation.
Alestalo (1971) also reported on the use of differences in wood to determ~ne
various stresses occurred to trees. Observations from these two authors
had been used in our earlier descriptive studies (McKendrick et al~ 1982).
3.2 Seed Dispersal and Germination
Be'· the type of seed (Howe and Smallwood 1982) and time of dispersal
(Densmore and Zasada 1983, Zasada et ale 1983) are important adaptations of
various species& Early colonizers are balsam poplar and willows which have
light seeds dispersed early in the growing season (Densmore and Zasada
1983). These early seeds have no dormancy and may produce cotyledons within
2 days of landing on a suitable site (Densmore and Zasada 1983). According
(
17
cited in Densmore and Zasa 1 98 3) , 11;1i ow s ee
seed coats and little or no endosperm ..
then other willows, aspen, and balsam
required 3 - 4 weeks for germination of 80% of the
" 1983).. Ware and Penfound (1949) and others have
h e
ies for cottonwoods and some willows.. Schreiner (1974)
poplar seeds may produce elongated hypocotyls and cotyledons,
enough vitality to produce a normal plant. Germination required
seedbed, and seedling survival depended on favorable conditions
one month (Schreiner 1974).
birch and white spruce seeds are relatively heavy, dispersed in
(Zasada et al.. 1983), and are dormant at the time of dispersal ..
of the fall-dispersed seeds germinated before summer dispersal
began (Zasada et al. 1983)$ This may have enabled them to take advantage
snow melt. Winged white spruce seeds may reach heights above the cone where
they were released and may travel circuitous routes (Zasada and Lovig 1983)~
seeds may also oe transported by water. Safford ( 1974) has
observed that spruce seeds may fall all year and that partial shade is
important for the seedlings. Birch seed fell all winter, hut only 10-15%
travelled over 51 m (Clautice 1974)a White spruce was considered relatively
seed and it fell within 64 m of parent. Mineral soils were generally
required for seedling establishment (Zasada and Lovig 1983, Zasada et al.
Fowells ( 1965, cited in Clautice 1974) reported that some species
became established on mineral soil exposed by wind throws, which was similar
to our observations~ The only young birch trees we observed in old poplar or
18
were on (
light shade 2 -3
germination started 1 week later than that its
later, and was more evenly distributed over
1974). This left spruce seeds more vulnerable to
season
some young to take advantage of better survival conditionse
\vater tables in late summer resulted in mortality from damping
overgrowth ~y other vegetation. June and August germinants had
on the north-facing slopes while July and August germinants
on the south-facing slopes.
3Q3 Flooding Effects
Fl coding is known to affect different species to different
Armstrong (1968, cited in Armstrong 1982) reported that some species have
adapted to flooding by having lenticels in the stem that provide for
exchange. If these lenticels are low and become flooded, the roots may
Fl. ood-adapted species produce adventitious roots in response to a
water table.. Lees ( 1964) observed that roots of white sprue e seed li s
de generated if waterlogged for too long. Hvwever, tolerance to flooding
increased if any foliage was above water.. He noted that even bog species
required aeration by lateral movement of water or \<later fluctuation. In
other words, moving water moving from a flood would not be as harmful as
impounded water, even if vegetation were subjected to these conditions
the same period of time (Kozlowski 1984).
Winter flooding and freezing might be harsher than summer fLood
because the ice prevents air exchange between the below-and
19
( is to many to
Even though plants are at time 9
1
pp caches were used in sampling t ve ta on
study., The initial study performed in 1981 was
be the various successional stages along the river and to
usefulness for moose.
frame was secondary.,
Determination of a successional
Unanswered questions regarding
and time frame for the various stages were addressed in our
sites in 1984.. Hence, sampling of ages was deliberately
r s
to
older individuals or coring fa 11 en 1 og s .. Densities were o y
recounted on browse species, and cover was only estimatad on early sites or
where changes were apparent. The only complete data set was collected
981 9 and the 1984 data were used to explain more details of the
succession and changes that have occurred.
4ol 1981 Methods
The original quantitative descriptions of downstream floodplain plant
communi ties were based on sampling 29 stands between the Deshka River
Chase (Figures 2-10). Reconnaissance of the area in August 1980 and again
early summer 1981 was used to determine the types of floodplain vegetation
present.. In June 1981 a series of points systematically plotted on aerial
photographs was classified by helicopter survey and used to determine the
relative availability of each of the types. Sample sites were then selected
in each successional stage in each of three reaches of the river: Deshka
River to Sheep Creek, Sheep Creek to Birch Creek Slough, and Birch Creek
Slough to Chase.
21
to allow
30-m transects., Initial data analysis
were needed for adequate sampling@ August, two more transects
tvere used in most of these stands (except two alder stan w wer
uniform) and four more transects were used in one of
birch-spruce sites (site 4)u Early successional stands were
transects in a homogeneous area where possible. However,
areas were too small and as few as two transects were used in some
places. Sometimes one transect would be taken in one patch and another in a
nearby, but not contiguous, area.
The 30-m transects with nested rectangular plots had been selected as
most reasonable way to sample everything from early successional sites
with sparse vegetation cover and small plants up to mature sites wi
dense, multilayered vegetation. It may not have been the best way of
sampling the early stages and the transect should have been longer some
the mature stages, but it worked well for a general de scription of the
stages, which was the original objective.. A more detailed study
probably use more but smaller transects in the early sites and either more or
larger transects in the later sitese The large scale of pattern presented by
trees made it difficult to sample across all the vari ability with o n1 y
a 30-m transect. Smaller sampling units would be better in the early stages
to avoid confounding of microsites. The problems with the transect size or
numbers of transects were not apparent until the sites were resampled
in 1984 and the data from the two years compared. In st a lla on of
may in ate much of e va y
cover by species was recorded on two to transects
50 em along a tape measure& Observation :ln
was aided by use of a set of cross-hairs a sighting
ecies. density was determined by counting e number
by height class rooted within a designated plot alongside
of the ~ransecte Shrubs < Oo4m, 0.4 to 2 m, and > 2 m but < 4 em
at
of
(diameter-breast-height) were counted in a 1-m plot alongside transect ..
shrubs (>2 m in height and > 4 em dbh) were counted in a 2-m wide
trees (> 4 m tall) were counted in a 5-m wide plots An individual was
as any stem emerging at the surface of the litter, whether it had
the same parent roots as its neighbor or not.
These size classes were designed to se para te brows able stems from
un brow sable stems., Woody stems less than 0 .. 4 m tall were considered
unavailable because of snow. Snow depths have never been measured on any of
our sites in the middle of the river where the environment may be different
from that on the snow courses which were located in forest openings at
Alexander Lake ( 1964-1982), Willow airstrip (1964-1982), and Talke-~tnc1
(1967-1982)0 Mean snow depths over these courses range from 0.7 m to lwO m on
the February 1, March 1, and April 1 readings. Given these facts and that
snow depth increases through winter, 0. 4-m depths may not accurately
represent late winter conditions in mid river.
Age, height, and dbh of important tall shrubs and trees were measured on
two randomly selected individuals along each transect in 1981. Important low
shrubs were also measured for height, length, and width. Heights of tall
cano
s a f
counting growth
or cores$ Ages of four individuals per transect were
emphasis on older individualso Measurements were also
1984 so that increase in height of vegetation in
own dominance was a measure of which species were capturing
sunlight., It had the following values: (1) open own (not
), (2) dominant -received sunlight from above and the , (3)
-received sunlight from above but not the sides, (4) intermediate
rely reaching main canopy, ( 5) overtopped -below general level
canopy, (6) subordinate -under overtopped, and (7) ground -lowest
dominance is very different from absolute height and is similar to
relative heighto Individuals in early succession sites may be dominant even
if they are only 0. 5 m in height if nothing else is growing above them.,
Five-meter tall stems may be overtopped or subordinate in later vegetation
stages, depending on the other vegetation~ This was not remeasured in 1
because the only places that it changed were where species had been virtually
eliminated.
4.2 1984 Methods
Methods in 1984 were designed to measure change and enhance
understanding of the successional sequence and time fr1me. All sites were
revisited to the extent possible. Two were on sand bars in areas with many
unvegetated and slightly vegetated bars that looked alike and were constantly
's
transect
transects
was not
was
were
transects were
were
y a deta ed photograph
was too
photograph through
poplar -
none were sampled in
spruce site was
limitations
of 1981 methodology, but
to a
in
was
according to
similar to that mature balsam poplar sites Ages were
the was explored to better understand the
to birch-spruce ..
several early sites woody individuals were excavated to
of stem (Figures 11, 12). Woody speciest such as balsam
, may survive frequent sedimentation which buries part of the stern ..
an individual was sampled at ground level, and the annual
counted to find 9 years.. When the plant was dug up, might be
9 years of growth buried. Not all stems have experienced that much
sedimentation, but most have had several years of growth
stems per te were excavated where cime permitted to analyze the
sedimentation history as illustrated by bent and buried plants. were
obtained in 12, an ice-affected te near Whiskers through
as
ss
scars on trees to
s es were visited during
break up
places. Browsed and
to
water s
were on
to estimate the relative number of available tw s and
in different successional stages, where utilization was
of twigs browsed.. This was not intended to be a browse
~ but rather to obtain general comparisons.
y successional communi ties common to t lower river
portions above Talkeetna are dominated by
, and combinations of these, or dryasG These types account
vegetated land on the floodplains as determined from
transects observed from helicopter in June 1981. These communities
little total vegetation cover and greater than 50% bare ground
3)o Plant species in these types characteristically have rhizomes, or
underground stems, which may extend for many meters and are
in binding loose sand and silt. Sprouts generally arise from these
n1zomes, thus increasing the vegetation cover in the area. Even sites that
are dominated by one of the woody species usually have a significant amount
of horsetail present except on very sandy sites.
When sampled in 1981, all the early sites combined averaged 25% cover by
(Table 3).. Sandier sites averaged mw:h less than this. Balsam
poplar averaged 8% and feltleaf willow averaged 4% cover on these sites ..
Other characteristics are summarized in Tables 4 and 5. The site histories
section will detail the changes between 1981 and 1984.
Although early successional sites had high densities of browse species,
many stems in the sampled areas were too short to be browsed. Only 4% of the
balsam poplar twigs were browsed while 76% of fel tleaf willow twigs were
browsed (Table 6). Stems had to be at least 40 em tall to be counted, but if
snow were deeper than that, unavailable twigs might have been counted as
available0 Hence, they could not be browsed. Many poplars might have fallen
feltleaf stems were
willow indicated it was a resource ..
5 1 .. 1
stands generally had more vegetation cover
sites with 46% total cover (Table 7).. Horsetail
cover while balsam poplar and feltleaf willow accounted for 2%
The dominant horsetail species on the early sites was
rennial ~uisetum variegatum. Some other species were probably
present, but certain identification was questionable because of the need
both sterile and fertile stems. The Eguisetum genus can sometimes be a very
difficult one for identificationo Sites that were dominated by horsetail in
1981 included 8, 15, 13, 1, 9, and 14.. Sites 8 and 15 were almost
exclusively horsetail while site 1 had considerable balsam poplar. Sites 9,
13, and 14 contained an important feltleaf willow componente
Woody stems in the horsetail sites, as in most early successional sites,
were relatively short, on the average approximately 50 to 60 em (Table B)~
This was tall enough to be counted as browse using the assumed 40-cm snow
depth, but if 70 to 100 em was a more realistic snow depth, then there was
little, if any browse in these stands that would be available in late winterc
The most important size class was < . OL~ m (Table 9) o Balsam poplar had a
mean age of 5 years above ground, while feltleaf willow averaged 3 years
(Table 8).
poplar stands were 7
cover (Table 10).. Horsetail provided y 5% cover in
willow still averaged about 50 em tall 5
age, but poplar only averaged 32 em height
above-ground age was 7 years (Table 11). Hence, growth on
was slo\..rer than on sites where horsetail was a dominant factor$
balsam poplar sites were usually very dry with a sandy soil
conditions. Sites with horsetail generally had a finer textured
more mesic conditions. Again, the size class with the most individuals
was < 0"4 m (Table 12). Sites 5, 20, 21, and 25 typified this type of
site ..
5. 1 9 1 .. 3 Willo\v
Sites dominated by willow had approximately the same amount of
vegetation cover as horsetail sites, 48%, but only contained 35% bare ground
because of additional litter (Table 13). Horsetail provided 25.% cover.
Feltleaf willow averaged 79 em height and 6 years of age while poplar
averaged 49 em and 7 years (Table 14). These sites provided better growing
conditions than the juvenile balsam poplar sites. Most willow were browsabl-
e while most poplar were still too short (Table 15). This kind of site was
typified by sites 6, 16, and 22.
·s .. 1 .. 1 .. 4 Others
Dryas sites, as typified by site 18, were characterized by 4% living
dryas cover, 7% dead dryas (centers of mats were frequently dead), SO% bare
' or ) '
6%.,
successional to to
Aging stands was d a
sediment around, not stro y, estab v etat
some areas (F' _ 1gures 11' 12) ~ The vegetation
poplar approximately 50 to 60 em in height 5 to
of growth since the last major sedimentation and another 5 to 10
of growth under the sediment. Ten years was a lot of buried
was not unusual to find 3 years of growth buried.
-~tail-willow and horsetail-balsam poplar plant communities provided
a substantial forage resource for moose. Close proximity with cover (mi1-and
late-successional stands) allowed most such areas to receive use by all age
of moose during all seasons. However, stands which were located far
from protective cover might only have been acceptable to older anima
Horsetail and dryas communities were of little or no value to moose at any
of the year, because the browse was either insufficient or too
low-growing.
Browse availability was based on an assumed 40-cm snow depth. In
:"'"eality, snow depths fluctuate through winter, not reaching maximums until
late winter. In mid-to-late winter, snow depths along snow courses in small
openings in mature forests near Talkeetna, Willow, and Alexander Lake have
been closer to 70 to 100 em over the past 20 years. However, none of these
snow courses were on the floodplain that the authors have been consideringQ
Wind action on the river may produce different results or early successional
sites may have more or less snow~ If those snow course measurements were
no
1 .. 2 ..
areas
since many areas
at that time
Histories
8
5 through 9 were early successional sites located near
Landing near RM 67, on the east side of the 8 was
site between the slough and an unsampled willow-horsetail
1981, it contained 48 % bare ground, 14% litter, 1% balsam poplar,
By 1984, however, the horsetail had expanded and less than
ground was present (Figure 13). The woody species had been reduced to
numerous current-year seedlings, shaded under the horsetail. The slough
adjacent to the site removed several feet of shoreline and became deeper.
A moss layer, similar in appearance to Rhacomitrium spp .. (but it
has not been identified), has developed, keeping the surface soil in
moss layer was noticed in several sites and was associated with
soils (such as silts and fine sands), and with good soil rno is tu re , but
without recent severe floodingo This might reduce soil erosion by wind and
water and have an unidentified effect on seedling survival.
The area occupied by sites 5 through 9 had bet.~n deposited since 1 1,
and appears to have been considerably affected by recent and rapid changes
in the adjacent river channels as indicated by comparisons of aerial
photographs for 1951, 1980, and 1983. The dryas site has been flooded and
silt deposited on some dryas. Some of the shallow sloughs through the island
seem to flooded frequently enough to prevent seedling establishment. The
rate,
more years ..
13
side,
31
site 9
in the last 3 yearso If river
horsetail site 8 will probably completely cut
at
13 \<18!,? a horsetail site at RM 100 above the confluence \'<lith the
It contained recent sediment deposition in mounds where ice
h m ted away.. The deposition was apparent in the hummocky
of some areas. Comparisons of photographs between 1981 and 1984
indicated an increase in horsetail cover and a lesser increase in willow
( However, the willows have definitely grown larger~
amount of bare ground has decreased from 60% to 42% while the amount
of horsetail cover has remaineJ approximately constant at 30%. Woody species
accounted for < 2% cover in 1981 while feltleaf willow now accounts for 14%0
Balsam poplar and alder provided only 1% cover each T..vhi le other willow
species provided 5% cover.
Balsam poplar densities in the < 0~4-m size class increased 2.2 times
from 1981 to 1984 although ~uch of that occurred along one transect. (The
increase was 1.5 times without that transect). Feltleaf willow in this class
was not detected in 1981, but much was present in 1984. There was 2.7 times
as much fel tleaf willow in 1984 as in 1981 over all size classes. Tall
ueberry willow (Salix novae-angliae) and littletree willow (Salix
also increased between the two years. Balsam poplar averaged
em tall and 4 years old while feltleaf willow averaged 127 em tall and 4
years old .. Feltleaf willow increased in size and abundance \vhile poplar
sameo site had in 1 so
years of growth might have been covered
accurate ..
west side of the island had been completely eroded 1
new material had been deposited to its west.. Mature
west ban~s of the river had also been cut away. Some areas
3 were only sand bars in both 1951 and 1980 while other is s
from it have become visibly better vegetated as indicated by
photographs o This site was vegetated in 1951 although not y
wer portions of it were flooded in the August 27, 1983, photographs
( daily flow 31,000 cfs Gold Creek) but not in the September 16, 1983
(12,200 cfs).,
5.,1 .. 2 .. 3 Site 1
Site 1 was a horsetail -balsam poplar site located just upstream from
the Susitna Landing boat ramp neal-Caswell Creek (RM 62 .. 3).. Vegetation on
this site has increased in cover and number of stems between 1981 and
1984 reducing bare ground from 79% to 51%.. Little change has occurred
between 1981 and 1984 for cover of the woody species, balsam poplar and
feltleaf willow while horsetail has increased from 10% to 26% cover. Moss
and ~~a rchantia spp .. , a low-growing liverwort, provided 2% cover in 1984 ..
These species sometimes provided sufficient ground cover to keep soil in
place, but vvere not as important at this site as at some other sites~
Balsam poplar stems < 0.4 m tall increased almost six fold between 1981
and 1984 while some individuals grew larger than 0. 4-rn tall in that time
period e The number ot feltleaf willow stems < 0 .. 4 m tall decreased
of stems 0 .. 4 m 2 0 m 1
the same as those in the smaller c in 1
by feltleaf willow during that time period has
individuals grew to be of browsable size*
average height of balsam poplar stems increased 51 em to em
willow grew from 67 to 127 em. The mean age
increased from 5 and 4 years of age respectively to 7 years
der that were present were about 4 years old both times,
were measured because few were available. Hence, the
seems to have advanced without any major setbacks between 1981 and 1984.
Changes have occurred in this part of the river since 1951~ The
of the river appeared to have shifted to the west side of the
site appeared to have been under water in 1951, although coloration on
the photographs indicated that it might have been a submerged bar~ some
islands below site 1 on the west side of the river, the river has become more
channelized since 1951 allowing the early sites to advance successionally
The main channel moved east of those western islands and deposited material
to the east of the channel.
New bars have developed just upstream from site 1 between 1980 and
September 16, 1983, as was apparent on those photographs, but these (as well
as part of site 1) were inundated by flows similar to the higher flows
of August 27, 1983. Increases in vegetation cover were apparent between the
1980 and 1983 photographs~ Many individual shrubs, particularly along the
sloughs, have been buried by silt but continued growing, indicating that
portions of this site were flooded most years.
was at
across a 17 15 -6
re s cies center than
was woody em
and
number of stems
stems
in
cover.,
in
constant.
1 feltleaf willow provided in
cover near 10% both years. Other willows
amounts in 1981 to 6% in 1984$ A
in some of the more moist horsetail and
site was present in 1951, but appeared longer and
Comparison of the 1980 and 1983 aerial photographs
maintained approximately the same shape, but was now more
This agreed with our observations from 1981 and 1984.
15 and 16 are located on same island complex which
• Some of these sloughs are
cover
to
several
sloughs running through
some are not, depending on depth. Most of sloughs flood during
water level (such as 31,000 on August 27, 1983, but not as at
12 cfs on September 16, 1983). Hence, the number and duration of
water events during a summer might directly feet this
particular, one of our permanent transects stretched y
ground to of a It started in horsetail-willow went to
more
in J y 84, when tn
along the lower reaches of the transect had
omes may still be alive.. The willow and
some high water during the summer k led
on this island complex during the July
g d
number of balsam poplar stems < 40-cm tall inc re as ed from 0
to over 12,000 stems/ha between 1981 and 1984 while those >
decreased from 10,000 to 1000 stems/hae There were more stems,
fewer browsable ones on the 1984 visite This could have resulted an
change in population size structure, from sediment deposition
the above-ground portion of the stems shorter, or from inadequate samplinge
total number of browsable stems of feltleaf willow has r ned
ap oximately constant, within sampling error. The < 40-cm size c
contained few stems in 1981~ but as many stems as the browsable classes in
1984. The change in conditions, or persistence of existing conditions,
apparently was favoring feltleaf willow browse production$ Other species of
willow seem to have decreased in density between 1981 and 1984.
Cover followed the same trends as density. Horsetail varied from 43 to
53% cover for the two years, probably vii thin the realm of sampling error ..
Fel tleaf willow ex hi bi ted a slight increase from 12 to 20% cover~ The
other willows decreased from 10% to negligible coverc
The willow poplar were 2 and 4 years of age in 1981 but alder was
not found& Both feltleaf willow and balsam poplar individuals averaged 5
years of age while alder was 3 years old in 1984o This validated the belief
that alder became established shortly after willow and balsam poplar. The
in
events
scour knocked vegetation aps
were preventi!1g vigorous growth and
5 2 Site 5
5 was a young balsam poplar site somewhat to the east and
8.. dominant change in this site from 1981 to 1984 was
wo y ec ies grew taller., Forty percent of the ground was bare
provided 41%, and balsam poplar 27% cover e This was an
amount of litter cover for a juvenile balsam poplar sitee Hor
e
for 7% cover in 1981. Balsam poplar and willow averaged 63 em and
78 em height in 1981, and might have been tall enough for browsing. Poplar
was oldest species averaging 10 years, while feltleaf willow and
averaged 6 years. The history of this site since 1951 was similar to that
already explained for site 8.
Site 20
Site 20 was a juvenile balsam poplar stand at mile 97.5 in the middle of
a group of shifting gravel bars just below the confluence of the Susitna,
Chulitna, and Talkeetna rivers. Difficulty in access to the site among these
shifting bars prevented a revisit of it during summer 1984. A helicopter
landed the authors in the general vicinity in May 1984 when there was too
little water to boat in the area. There was no sign of recent moose activity
at the time.. In particular, no stems had been browsed that winter. The
general complex of islands appears to have grown larger since 1951.
5
was a
not
< ,.4 m
, or c
rer
21 ..
21 was a
difficult to
on the island ..
poplar site
river
A similar was
been same one.. Both bare ground was
were 38,000 of balsam poplar < 0.4 m
984,
poplar covered approximately 1 2% in both
and the few willovs were 7
was only 4 years old in 1984, supporting
follows vJillow and balsam poplar :in colonizing a
was about 65 em tall and feltleaf willow 73 em tall
was sandy and arid.
5.1~2 8 Site 25
Site 25 was a juvenile balsam poplar stand at RM 84 .. 5, just
from Parks Highway This was a typical sandy poplar
ground, 5% cobbles, and only 5% litter~ Poplar provided 14% cover
feltleaf willow provided 3 and 1%, respectively. Densities
poplar were 6, 600 stems/ha, but almost 29,000 were
then 0 4 m tall., The willow and stems present (
1'"
were over l 2 m~
even a snowfall winter ..
mean above-ground for poplars waR 9 9 6 f
4 for alder$ This was a site with
portions of the stem accounted for 5-10 addi
poplar did not appear to be browsed very much dur e
winter, but been heavily browsed in the past.
stems were those near alder, individual stems in the open were
ss frequently .. Some moose tracks were present, but no fresh
were observed in May 1984.
There were LO obvious changes in the shape of the island from 1 1 to
t and the island had little vegetation in either aerial photograph e
, a strip of taller vegetation which existed on the we~t side of
the island in 1951 had disappeared by 1980.. The lower end of the
be came more ve ge tate d during this time period, although there was some
vegetation in 1951, particularly along the draws. Some established
vegetation upstream from site 25 in 1951 was eliminated by 1980. Vegetation
appeared denser in 1983 than 1980.
The island has probably been present the entire time between 1951 and
1980, judging from its shape,. position, and depth of sands on it. The
vegetation was still juvenile either because something was periodically
eliminating it or site conditions were prohibiting the maturation of
individuals.. Excavated poplar stems had become established initially
approximately OGS m below the present soil surfaceft That is, approximately
1ce
years
22
22 was on an early successional island a
vegetation communities near RM 54 (Figure 10).. was
from site 29 but downstream from sites 23 24., woody
were dominated by fel tleaf willow and balsam poplar , but ho rs et ai 1 was
Portions of the island were used by gulls for nesting a very
algal and moss crust on the soil surface indicated the bi s
significant amounts of nitrogen fertilizer. Alder also occurred in
a areas and probably enriched the nitrogen content in the area.
The higher portions of the site became better vegetated by 1984, but
gullies were becoming deeper by erosion. Almost SO% of the sampled
area was bare in 1981 while only 13% was bare in 1984. Horsetail cover more
than doubled between 1981 and 198L~, having 53% cover in the latter
cover was almost negligible on the first visit, but had increased to 15%
cover in 1984. Balsam poplar and feltleaf willow provided similar amounts
of vegetation cover both years, but they decreased from 9% cover in 1981 to
3% in 1984.. There were approximately 5 times as many stems of poplar as
willow in 1981, but all the poplar were less than Oe4 m tall, and all the
willow were 0.4-2.0 m tall.
Both willow and poplar were 6 to 7 years old while alder was aged near 5
years.. Both dominant spec:J. : ~·; were 1. 5 m tal1. on the average in 1984 and
available for browse. Although alder was usually slightly younger than e
on was a p nt
more
ss land was generally available for in 1
, but the study area appeared above water . v1ere
to become elevated above the .. By 1980
near that reach :tad been eroded, but more bars were near
existing bars were becoming more vegetatedo More vegetation was
gullies appeared more distinct on the 1983 photographs An
to the east has had the upstream end eroded, but this island has
a nnew" bar appear close to it.. This new bar has a similar s pe G
Although the study island had been in existence for a number of years, it was
to much river action and probably would not reach a mature stage
the river changed significantly. Although vegetation was developing on
island, gullies seemed to be getting deeper and dissecting the island$
Eventually the island might be eroded completelye
5&1~2~10 Site 18
Sitt 18 was a dryas site on the right side of the river at RM 96 below
Talkeetna. It was predominantly a cobbly site with dryas and a few areas of
deeper soils where juvenile poplar and horsetail could grow. The site
was very simj la-r between 1981 and 1984 although there appeared to be more
horsetail and silt in 1984.. This site seemed to flood approximately every 5
years, since above-ground ages were 4 to 6 years anrl below ground ages were 4
to 6 years ..
This site was in existence, but relatively bare, in 1951. It contained
low vegetation over much of the area with some taller shrubs, such as alder,
41
as
\..rere so in the area,
site has either or
just recently acquired enough sediment over the
besides dryas to grow, or poplar cannot
The frequent flooding or scouring hypothesis was
protected areas and pockets in the terrain of this
relatively deep soil (50 ern). The central sloughs of
f on
to receive frequent flow, as water which overtops the at
upstream edge of this area flows into the sloughs.
above and below site 18 have been eroded since 1951 :t including
relatively mature vegetation near the center of the channelc The channels
near this site appeared wider in 1980 than in 1951. The Chulitna has
additional area between 1980 and 1983. Since areas near it were being
eroded, this site was probably flooded frequently.
This site also provided some interesting insights into browsing, at
for balsam poplar8 Individuals that were browsed were generally older
and taller than the unbrowsed individuals, even those greater than 0 0 4-m
tall.. Snow depths in the area might average 1 .. 5 m, rather than the 0 * 4 rn
assumed from a study in Denali, the most useful information available when
the study was initiated.. This might account for the number of unbrowsed
"browsable" stems .. The browsed stems also appeared to be away from feltleaf
willow or near alder. One interpretation of this was that when moose were
near feltleaf willow, they ate willow rather than the poplar, but if they
were near alder, they ate poplar rather than alder & (The authors are
not proposing that this single observation Ehould lead to the conclusion that
5 ..
5 .. 2
cover
to where
Successional Stages
Descriptions
areass Moose
of sands and
the elevation of
and/or deepenJ.ng
farther above
over
)
were
cover
eaten
to
ve 1 of f
s us f re om from disturbance from ice
ent
water
to be necessary for transition of early successional to
These mid-successional types accounted for
vegetated land in the floodplain. Mid-successional
was ac terized by thin leaf alder or immature balsam poplar
into tall shrubs or trees. The alder type the phase
mid-su~cessional stage and appeared to last from 15 to 30 years
stabilization (Figure 15). The immature balsam poplar stands
to dominate the vegetation to 55 stabilization, but were
than the alder type~
Total vegetation cover in alder stands aver&ged 87% (Table );
provided 59%, whereas balsam poplar pr ovid o y 13% cover.. A
st king jifference between ea y and mid-successional stages was the
Dare in
canadensis covers were 99%
-<~_,_,;;;;.._ __ _
increased over that s
to stems/ha), whereas balsam poplar declined from 40,
(Table 17) .. Crowding, competition, and preferential by
moose may account for some of the reduction of a
plqnt which enables it to perfLrm than
on young, inf~rtile soils since nitrogen is frequently limi"""
may enrich the soil so that other species grow better in ater
does not grow well in the shade of the taller alder this
velo pmen t stage .. However, shade tolerant species s·Jch as
y rose, and highbush cranberry appeared on these siteso
The average ages of tall shrub-sized thinleaf alder and balsam poplar in
stands were 20 and 19 years, respectively (Table 18)o Because
cycling that occurs in early successional stages and the fact that most
stems took root considerably after island stabilization, these islands were
probably stabilized 25 to 30 or more years ago .. Balsam poplar and
heights were nearly equal, 7 .. 9,and 7 .. 0 m, respectively in the alder stand
However, observation of many different aged alder stands suggested that o
balsam poplar reached the top of alder canopies, the balsam poplar quick
doubled its height, thereby overshadowing the alder and developing into
immature balsam poplar phase of the mid-successional stagec The alder pha
was typified by sites 27, 23, 2, and 19.
Balsam poplar dominated the overstory of i~nature balsam poplar stands,
producing 62% cover (Table 19); thinleaf alder provided 40% cover. As in
alder stands, there was essentially no bare ground and litter and bluejoint
on
covers were 99%
0ver that
to 6682 stems/ha), whereas balsam
17).. Crowding 9 competition,
account for some of the reduction of balsam
plqnt which enables it to perform better
infertile soils since nitrogen is frequently
enrich the soil so that other species grow better. in
a
does not grow well in t:he shade of the taller alder during t s
velopment stage.. However, shade tolerant species such as
rose, and highbush cranberry appeared on these sites ..
The average ages of tall shrub-sized thinleaf alder and balsam poplar in
stands were 20 and 19 years, respectively (Table 18). Because
cycling that occurs in early successional stages and the fact that most alder
stems took root considerably after island stabilization~ these islands were
probably stabilized 25 to 30 or more years ago .. Balsam poplar and alder
heights were nearly equal, 7.9,and 7.0 m, respectively in the alder
However, observation of many different aged alder stands suggested that once
balsam poplar 1·eached the top of alder canopies, the balsam poplar quickly
doubled its height, thereby overshadowing the alder and developing into the
immature balsam poplar phase of the mid-successional stage. The alder phase
was typified by sites 27, 23, 2, and 19.
Balsam poplar dominated the overs tory of 1rnmature balsam poplar stands,
producing 62% cover (Table 19); thir1leaf alder provided 40% cover. As in
alder stands, there was essentially no bare ground and litter and bluejoint
most covere
trees
21),
from 3559 to 352 stems/haQ
substantially increased in density (Table 20),
more robust growth forms (Table 2l)o
poplar trees in immature balsam poplar stands averaged
( e
rose
22) and 18 m in height, which was more than double their height
phase.. Alder ages were about the same in both the alder
balsam poplar phases, suggesting that approximately 20 years
of individual alder stems. Balsam poplars in the immature
ar s ta s were among the early colonizers of the island, while
alder stems in these sites must be second growth. Heights of alder were
also roughly equal between the two phases and it was apparent that thinleaf
attained a greater height than Sitka alder (Table 22). Immature
poplar sites were typified by sites 10, 26, and 12-
spruce was found as early as the alder phase (34 stems/ha), tvith
the number of individuals only slightly increased in the immature balsam
poplar phase (Tables 17 and 20). Age data (Table 22), however, suggest that
most white spruce individuals were established sometime after alder stands
began developing into the immature balsam poplar phase.. This discrepancy
could indicate sampling was insufficient to cover stand variability and/ or
that considerable mortality occurred with young white spruce in this early
period of their establishmento Nanson and Beach (1977) has also noticed this
phenomenon in British Columbia.. Paper birch alsc was found in both
mid-successional phases, but the age differences between phases (Table 18 "~
) no increase in of as
may strongly affect some of the stems in these
stems are rigid enough that when they get knocked down
immature
sites.,
t sp back as the more resilient stems of the
doc However, they are not so rigid that they are
stages~ The bent stems may then resprouto The
in the same stage that it was before the ice scour, but it has a
younger age structure. For instance, if a 20-year old alder stand were
by an ice jam flood, 1-year old stems would be present next
growing vertically from the horizontal 20-year stemso Hence the age
distribution has been reduced from a mean of 20 years to a mean of 1 year
is may occur repeatedly along the same sections of the river, but it
usually occurs only in localized positions where jams occur f requen y
(Figures 16, 17)0
The amount of damage and vegetation stages affected would be determined
by the size of the ice jam. For instance, near Whiskers Creek (cross section
LRX-7, site 12), jams occur almost every year.. The uppermost end of the
island has early successional vegetation that gets knocked back and buried
rather frequently. An alder stand occurs slightly downstream and portions of
it \.Jere last leveled nearly 2 decades ago e Further downstream was an
immature balsam poplar site with several scarred trees, some scars 2 m above
ground~ and some trees have several sets of scars from the several times they
had been scraped. Repeated scraping may affect the vigor of the plant, but
it does not usually cause retrogression to an earlier vegetation stage
rose (
cces p nt commu ties gener h fewer stems
to moose or
the diversity of browse was greater wi presence
species such as highbush cranberry, y
6) .. Mid-successional communi ties also provided a mix
important in the diets of young calves and lactating cows o
and immature balsam poplar stands pr ovid ed dense hiding and
cover.. Alder stands, having very low browse densities (
a rela vely unpalatable species), exhibited extremely heavy
of balsam poplar, indicating moose may have been using
during severe weather or at other times when they were compelled to
thereo
Sometimes these intermediate sites occurred in very narrow strips around
islands and were too small to sample using our techniques. They maximized
edge e ff ec t for wildlife.. More importantly, willow remained relatively
abundant in these narrow sites, which had more sunlight entering from the
sides than in more intensive intermediate sites. Most of these willow are
tall enough to be available to moose even in heavy·snowfall years.
5G2.2 Site Histories
5 .. 2 .. 2 .. 1 Alder
5.2.2.lel Site 27
Site 27 was an alder site near RM 75e5 below Montana Creek on the west
side of the river (Figure 7) that had been flooded and received sediment
between 1981 and 1984. There was little understory relative to other
mosses were early
with
vegetation cover was provided by (67%)
oplar (24%) $ Bluejoint only accounted for 4% cover, ereas in
1-developed Sl tes II it provided nearly 50% ground COVer e
that this site was disturbed more recently than o
The number of balsam poplar stems appeared approximately same
1981 and 1984, approximately 2000 browsable stems/ha9 were a
number of alder stems between the two years, but the size class
distribution changed somewhat. There were fewer browsable stems, but more in
2-4 m tall, > 4-cm dbh categoryo
The oldest balsam poplar cored was 23 years old with above-ground ages
ranging from 10 to 19 years in 1984G Cored alders varied from 14 to 18 years
of age while f el tl eaf willow varied from 12 to 17 years .. The largest
poplars exhibited good growth in the last 6 years. The uneven age structure,
plus the unknown number of years of growth that might be buried by
made it difficult to determine which species came first.. Poplar might
be somewhat older than the others, and the open nature of the stand permitted
reproduction of poplar, a rarity in alder stands. The small size of the
stand made edge effect very important, and, in fact, more pellet groups were
found near the edge of the stand than toward the middle in May 1984.
Considerable sediment deposition has occurred on or upstream from stand
27 since 1951., It was a relatively unvegetated, but stabilized island in
1951 0 Areas upstream that were slightly vegetated in 1951 now have
No
to
2 1 "2 e 23
was an site near RM 55 and upstream on
east the river (Figure 10).. It was not resampled in 1984
almost eliminated it~ The vegetation in 1981 was dominated by
cover), balsam poplar (22%), and bluejoint (58%)o were a
shrubs and forbs$ Approximately 50% more stems of alder than balsam
> 4 m tall were present. Other size classes provided less than 670
stems/ha each9 All balsam poplar in this stand had been heavily browsed in
the , and numerous dead branches w·ere attached to the trunk.
Th site, typical of alder sites, was dominated by 73% cover of
thinleaf alder and 53% cover of bluejoint. Balsam poplar provided 22% cover
in a site with almost complete vegetation and litter cover. Most thinleaf
alder were approximately 25 to 26 years old, but age ranged from 19 to 32
yearse Most measured balsam poplar were 25 to 27 years of age although some
were near 20 years.
This site had very young vegetation and was almost bare in 1951 which
would account for ages < 30 years. The surrounding stable vegetation
indicated that this site had been in existence for a period of time, so that
the lack of advanced vegetation might have resulted from a catastrophic event
such as an ice jam or flood rather than exposure of new land surface by local
deposition or downcutting of the river. Erosionn and depositional features
were obvious throughout the site in 1981. Most of this area was vegetated
with alder by 1980, but the uppermost point still had relatively young
was
area a eared la er in 1984 than in 1 and was to
Se2.,2.1.3 Site 2
Site 2 was an alder site, just above Susitna Landing t
downstream of Caswell Creek, and just east of site 1 (RM 62.4) 9)
Cover was not remeasured in 1984 because it had not changed much~ had
total vegetation cover and complete litter cover in 1981., r and
bluejoint reedgrass each accounted for 29% cover. Feltleaf willow provided
8% cover, poplar 3%, and horsetail (Equisetum arvense) 4%.
Ages were redetermined to estimate the age of the site rather than
average age of individuals as had been done in 1981. Several s
were found to be 29 or 30 years old, although most were in the 22 to 26
old bracket. Several individuals had small annual rings approximately 11
years ago, indicating that 1972-1973 may have been a poor growth year
generally or a flooding event caused growth rate reduction in this site G
Because rings reflect growing conditions in more than one year, they are not
a precise method of indicating when such ev,ents occurred. Ho\vever, there
were significant fJ.oods with flows greater than 80,000 c:f:s (Gold Creek)
discharge in 1971 and 1972.
Although this site was near site 1, it was on the east side of tlte river
and was not affected by many of the river changes in the area~ It was bare
ground or early successional vegetation in 1951. Apparently the island
1
are 30 is not common
y of vegetation development. Hence, a s
l photos for alder to ~ecome established was
above-ground ages so it was possible that several years
.... l. 4 19
19 was an alder site located at RM 94.5, nearer the east bank than
bank, but still in the middle of the river. It was abnormally high
the water for an alder stand. There was twice as much willow in the
in 1984 as opposed to 1981 and a significant reduction in the amount of
alder. Most of the alders counted in 1981 were > 4 m tall while none was
recorded for that size class in 1984.. Additionally no balsam poplar were
recorded in 1984, but 1500 stems/ha were counted in 1981. Much of this might
have resulted from inadvertently locating the transects in different portions
of the stand because of the stand's patchy characteristics and the relatively
small length of the transects. Sampling error may have accounted for some
of the discrepancies.
The oldest individuals were balsam poplar aged 25 to 26 years old. The
mean age for poplar was 18 while that for alder was approximately the same.
Changes to this site between 1 J80 and 1983 were negligible, but
vegetation above it had been slightly cut on the upstream end of the east
side. A channel on the west had bent further to the west after passing this
stand between 1980 and 1983. The channel on the east was taking a more
gradual turn to the w1est in 1983 than it did in 1980. The result was a
5
in L
5 2 2~2 Balsam Poplar
~2.2.2el Site 10
10 was an irmtl?. -Jre balsam ~ dr site at RM 67 .. 5 above tna
and just a short distance ups~ream from sites 5-9 (Figure 8)0
te was heavily used by beaver, as indicated by the number of balsam
cut down.. The number balsam poplar stems in the 2 -4 m but < 4 em dbh
class was reduced from 988 to 42 stems/ha between 1981 and 1984~ Some
might be attributable to s;: ~pJ i :ag error, but much of it resulted
as indicated by number of ~pse The visual appearance of the stand
between 1981 and 1984. Since alder was not a browse species, it was
not recounted in 1984 so no ccmparisons can be made for any changes in it~
However~ 17 stems/ha of balsam poplar > ~-m tall were found in 1984, but not
1981. Conversely 67 stems/ha were found in 1981 in the 0.4 -2.0-m class but
not in 1984 .. Apparently the smaller stems have either grown to the
size class or been eaten but some of the difference could be attributed to
sampling. Alder stems totalled almost 3,000 stems/ha in 1981 across all size
classes. Feltleaf willow stems decreased from 1000/ha to 83/ha.
The cover measured in 1981 was dominated by 43% alder, 28% balsam poplar
and 39% bluejoint ~ Litter covered 100% of the area. Other species all
accounted for less than 2% cover each.
The oldest alder stem cored was 30 years while the average age was 21 in
1984. Most individuals were 16 to 23 years olda The oldest balsam poplar
was 42 years old and had its best growth in recent years after it had
of cores
1951;
to Only one individual was over
became av r colo za tion a
y recent have
in area ..
corner of island had a patch of vegetation on a
This was probably a dryas site
enough soil to support other plants .. However, the
at site have prevented normal vegetation development~
stun ted and balsam poplar (partly because they are ) as
as a few forbs such as asters and astragalus. The of
might last at least 30 years and might persist much longer
additional sediments are deposited there.
Since 1951 the main channel of the ri;er has moved to the western
Apparently the entire site (including the cobble area) became available for
colonization g The river changed course before it had deposited
sediment over the cobbles normal plant growth. In contrast, nearby
te 7 might a uire sediment suffic nt for better plant growth
succession unless further changes in the river reduces s imen ta ti on or
eliminates the site by erosion~
was an at
near site
approximately 400 sterns/ha of balsam
y less than in 1981 althoagh this
of alder stems was similar between the t\vO
stems/ha.. Cover values were typical for a
poplar, 60% alder, 7% low shrubs (rose and highbush
23% bluejoint* Several forbs produced less than 1% cover each~
Balsam poplar ages ranged from 40 to 66 years.. Several
in
error.
%
)
began more rapid growth about 25 t.v 30 years ago when they were 20 to
old. This was probably when the poplar overtopped the existing
oldest alder cored was 30 years old, but most were around 23 years
of age. The rings on the alder were relatively small for the rapid
rates associated with alder in the open* The relative size of rings and
ages of individuals of the two species supported the hypothesis that the
poplar grew more rapidly after overtopping the alder, and that the alder
esen t in an immature balsam poplar stand were probably second
developing beneath the poplar canopy$ No changes in this area were apparent
from the aerial photographs other than the general ones described for site
25.
5.262.2.3 Site 12
Site 12 was an ice-affected immature balsam poplar site near RM 101 .. .5
near the mouth of Whiskers Creek (Figure 3). Site 12 was in the oldest
portion of the island. Upstream from this was an alder site that might
on it,
it was
of the variability within the island, 6 transects were in
probably covered both the immature balsam r
, "t~rhereas only 2 transects were used in 1984 and were in
the island. Six transects could not have been located on only
r port ion in 1981 .. Hence, the two sets of data were not y
No rose or highbush cranberry were detected in the 1984 transects
they w~re definitely present at the site. Stem counts for balsam >
4-m tall ranged from 251 stems/ha in 1984 to 791 stems/ha in 1981 ..
higher count in 1981 probably resulted from including portions of the
younger site with higher stem densities.
Vegetation cover at the site consisted of 72% balsam poplar,
thinleaf alder, 14% Sitka alder, and a total of only 5% for low shrubs
bluejoint. This sjte also had only 80% cover by litter in 1981, a low
value for this type vegetation~ This site was subject to flo ing and
sediment deposition both from ice jams and from summer floods. This made it
difficult for some species to survive, and also covered some of the littere
This site appeared to have relatively uniform-aged, developed vegetation
on the 1951 aerial photographs except for the upstream end.. The 1980
photographs indicated a relatively barren area at the upstream end, inter-
mediate vegetation next, and older vegetation on the downstream end. Willows
were bent on the north side of the island in 1981 after an ice jam~ Most
changes were attributable to ice, but summer flows were responsible for new
0
scars ice approximately 2 m above
~ When ice scrapes vegetation it s
which is essential for new wood growtho Without to
new wood, a scar forms, which has no las ng effects o e
structure~
north side of the island contained most of the ice effects$ of
stems in the alder portion had been bent over then
20 years ago either from the bent stem or from the surviving root
i\w
if th2 above-ground stem was too badly damaged (Figure 20).. By
these individuals, an idea of when these catastrophes occurred can be
Another island occurred just downstream from this study area. This was
in 1951, but was well vegetated in 1980 with tall willows and alder ..
Site 12 was first visited approximately 2 to 3 weeks after an jame
Willows on the north side had been bent at approximately a 45 degree
may have received a few scrapes, but did not appear otherwise
The upper end appeared barren at first with piles of sediment having
deposited by melting ice blocks and some areas of soil having been pushed by
\1)
the ice (Figure 1 7) .. Closer examination, however, revealed young willow
plants poking through the debris. In addition to being matted down, they
were also scraped in places~ but they ;..;ere beginning to leaf out.. The
portions above ground appeared to be only a few years old. However, the
presence of even a few stems could make a big difference in successional
rates because these stems could propagate vegetati.vely rather than waiting
15
3
5.,3 1
on
to
cores on
was on
to scars on some young
one
was 36 yearst with
Stages
Descriptions
old was
site were
y
to
stems
.. Almost
18
40 years
y.
stems
were 10 to
tree
growth being
balsam poplar stands matured, white spruce
in canopy. Mature balsam poplar stands possibly occurred
island stabi zation and extend for another 80 years (F ure 15) ..
, the balsam poplar becomes decadent leaving space
of te spruce and paper birch, if no major disturbances interrupt
Balsam poplar cannot generally reproduce in shade a mature
White spruce appears to shade tolerant ~nd new individuals seem to
in a random time frame. Paper birch 1 and
grow in the soil on the back of uprooted mature trees. Hence,
cannot become established until older trees
would occur was probably 70 years after island , but was more
100 years after stabilization. Mature and decadent
to f
to 32% area.,
balsam poplar stands,
cover.. Balsam poplar trees provided
cover, highbush cranberry 21%, prickly rose 15%,and
trich fern (Matteuccia was also an
1 (
,.,'"' ......... at of the understory (7% cover) not typically fou in ot r
communities.. Ostrich fern occurred primarily in mature
balsam poplar stands north of Montana Creek but be lo \~.· rt e
was used heavily by moose in June.. These ferns have not
nutritionally, but other fern species contain high N levels d
y spring growth which could provide a rich source of protein
upon digestibility of the N compounds in the fern~
owth characteristics of prickly rose and highbush cranberry,
dominant browse species, were not much different from those in the immature
stands (Tables 21, 24) but densities increased from 22:56 to 12,361 and from
1093 to 23,555 stems/ha, respectively (Tables 24, 25) .. This increase in
understory was likely a result of reduced competition from the overstorv
balsam poplart which experienced natural thinning (from 1045 to 294 ~tems/ha)
as it developed into the mature and decadent stage.
Mature and decaden~ balsam poplar 3veraged 26.4 m in height and averaged
98 years in age, a::::cording to our lY81 measurements (Table 26), Oldest
balsam poplar trees measured in 1984 were approximately 170 years above
ground .. When one considers delays in sites developing vegetation and the
partial burial of trunks, an additional 20 years could be added to the
de te rmin ed by the core to estimate the time since island stabil
were older trunks, an mean
many poplar individuals were 110 to 140
alder were extremely long-lived relative to
stages, and thus the mean age was 50 years~
-white spruce communities were characterized by 42% cover
and 12% cover by white spruce in the overs tory (Table 27) ..
predominantly thinleaf alder, accounted for 14% cover.. Low
,and grasses provided 40, 44, and 18% cover, respectively.
average height and apparent age of paper birch trees was 15.5 m and
years on 1981 data (Table). Again, the 1981 estimate was low
our inability to read rotten trunks, but our 1984 data "-'~re
older trees. Ages of mature birch stems have been measured in
120 to 140 year range in 1984 9 Hhite spruce averaged 16.2 m and 91.
rears. thinleaf alder (> 4 m height) averaged 5.5 m and 28 years~
The density of paper birch trees was 227 stems/ha (Table 29). There were
.43 white spruce/ha and 1792 alder (all sizes)/ha. Browsable willow, paper
Jirch, high bush cranberry, and prickly rose had den si ties of 20 0, 7 50 ,
.7050, and 16950, respectively. These shrubs were about 1 m tall (Table 30)e
Birch-spruce stands had the greatest variation in stand structure of the
·egetation types found on the floodplain. There was some evidence that these
:tands were self-perpetuating.. That is, upon decadence the birch over story
alls, making the spruce more susceptible to wind-throw and thereby allowing
paper birch shrub-alder/highbush cranberry-prickly rose community to
ncr ease.. The shrub community then 'progresses to the birch-spruce forest
ond i tion again .. The woody species composition and density of the seral
rush phase make it ideal moose habitat, especially as it is interspersed
mat-ere
, mature
resource moose
ea y successional stands, but
rose, birch (in birch-spruce
abundant.. The dynamic nature
of the stands from overmature overstory to
t n ck to mature birch-s uce) made this type
year-round habitat for moose ..
5.3.2 Site Histories
So3o2.1 Mature and Decadent Balsam Poplar
Se3.2.1.1 Site 3
Site 3 is a mature balsam poplar site above sites 1 and 2,
to the west near RM 64el (Figure 9)6 Cover of balsam poplar,
highbush cranberry, and bluejoint reedgrass 1ncreased between 1981 and 1984.
This could be an artifact of only running two transects in 1984
Ages of individual poplar stems reached 127 years with most individuals
the 112 to 119 year bracket. Several individuals grew more slowly
70 to 9C years, however, one grew better after years.. The
the rings could sometimes be a general indicator of what was
of
to a
stand, some individuals might growing in shade while others took
a canopy opening grew more rapidly ..
3 was of a larger, in
and partly knocked back to bare
from the same westward migration the
2. Some areas were eroded while other areas were
1983.. Mature vegetation on these sites had
or
er been
down and flooded away, making room for new succession or the
area was washed away and new sediment had been locally redepositedo
island to the west of site 3 had been eroded since 19510 The west
of the island with site 3 was a cut bank with overhanging trunks and
brancheso The adjacent slough was not safely navigable in May 1984 because
of , debris, and overhanging trunks.
5 3o2ol®2 Site 24
Site 2 4 was a mature balsam poplar stand near RM 56 above site 23
(Figure 10). It was dominated by 64% cover of balsam poplar and 54% cover
alder.. Highbush cranberry and rose each provided almost 30% cover~
Blue joint and field horsetail (Equisetum arvense) accounted for 5% cover
each,. As with most of these intermediate and mature sites, 1 it te r was
everywhere and total vegetation cover was > 90%0 Mature poplar trees provided
570 stems/ha.. Browsable rose and high bush cranberry pr ovid ed 2 4, 00 0 and
27,000 stems /ha while smaller stems of high bush cranberry provided 6900
stems/haG
Ages on the cored balsam poplars ranged from 69, 11~5, 152, and 130
years. White spruce was aged 107, 115, 105, 120, and 111 yearsG The few
alders that were cored ranged from 32 to 43 and 45 years~ One old birch tree
was found to be 11+9 years old and a young one was aged 7 years. Again,
to e
stems were (or
a a tree
occur most
sapling washed
ago, and or t was
that might found a site.
was near the east bank of the in not
much Another possible explanation was
become a birch-spruce forest at some time the past, or at
a individuals were present, then something happened to
t, or most of except for either some buried se s or some
Balsam poplar was then able to colonize
areas .. The soils at the site do not appear old enough to support
hypothesis. This site also had young birch trees growing soil on
sides of roots uprooted trees ..
Much material baove site 24 had been eroded between 1 and 1980c
Additionally, a bar opposite it had migrated downstream. An exteens e
slough to its east have become more channelized or narrower the
of the sloughs had become vegetated. The river used to be relatively wide
at this area, but deposition between 1951 and 1980 on the west side of
river and the downward migration of the bar have constrit~d
This constriction appears narower in 1983 than in 1980, but the river
broken through the bars on the west side of the river.
7
7 \'las a mature balsam plar site just
at 98.8 (Figure 3)o It had a relatively cover
from to 49% in 1981 and 1984, respectively, probably
error. Some of this variability Y
in 1984Q The main species included alder (36 -49%)~
(23 to 32%), and devil's club (Ec~inopan~~ (6 -14%) Some
species had a very patchy distribution and were found only some
of the stand. There was more gymnocarpium in 1981 gut more rose
highbush cranberry in 1984. White spruce accounted for < 5% cover
bluejoint provided 2%. Litter accounted for less cover in 1984 possibly
because of floods in July 1981. When the site was visited in early August
1981, '"ater still remained in the low areas and sediment had completely
covered all the littero
Densities were the same between the 2 years sampled although highbush
cranberry stem counts decreased from over 13,000 stems/ha to not being
recorded in 1984. This was probably related to the patchiness of the site.
Highbush cranberry had difficulty reproducing when flooding occurred because
it takes 2 years to germinateo
Much of the ostrich fern and some of the devil' s club had been eaten
when the site was sampled in June 1981. Two moose were observed swimming to
and from the island and beds were found in dense patches of the fern ..
\)st!it\\ I~!l\ %!0~S to \)~ OV~! 1 m tall snn wem1n prc'nably nave been about l-m
tall at this time (early June). Many individuals had less than 20.-cm of
fronds showing at this time; the rest had been eaten, presumably by the
moose. The plant appeared adapted to grazing since new fronds were visible
easy to
were to crown
moose
most
cored was
to
cored was 143
appeared that
things could have
1
while poplar rings were sometimes
missed on the poplar, resulting in an
a
most
were
Sometimes the poplar cores crumbled when them
to 120
trees. :i.dditionally the poplar have been flooded and partially by
many times, even after they were relatively mature. Soil
this and other sites in 1981 revealed multiple alternating
matter mineral soil which resulted from floods
was observed between June and August 1981. Normally spruce not
established on site until the amount of flooding and se mentation d
subsided .. Hence many more years of poplar growth might be bur:Led
ground than for spruce.
The site appeared to be well vegetated on all three sets of
photographs, but the downstream end the island was being eroded
Chulitna. This was noticeable even between 1980 and 1983. It had
on sides parallel to the river. Debris had also been piled across the slough
on the Chulitna side. This debris had been overtopped sometime probably
the 1981 floods or 1982 breakup and sediment deposited behind it to a
not present in e photo t I-res in
new island was visited in 1984 and most of were
to 2 or 3 years old" Both ff=l tleaf willow
some horsetail were presentQ This implied that initial
any one species. The different phases of early successional
we have observed probably resulted from site conditions or events or
competition that developed with time.
563$2~1.4 Site 28
Site 28 was a decadent balsam poplar stand just below Montana Creek and
just downstream from site 27, an alder site near RM 75.7 (Figure 7).
over story was dominated by large balsam poplars, most of which have rotte!n
centers Hence, no accurate ages could be obtained in this site. Some of the
larger poplars had broken trunks, several meters above the ground. None of
the trees had been uprooted so there was no place for birch seedling
germination and establishment.
There were many openings in the canopy with the tree cover providing
only 42% cover, but the understory was well-developed.. Alder had 43% cover,~
most of which was in individuals > 4 m tall. The 51% cover of low shrubs
was divided among highbush cranberry (34%), rose (12%), ribes (14%), and
raspberry (10%). Bluejoint provided 24% cover and forbs 41% cover dominated
by ostrich fern ( 17%) and other species.. This well-developed understory
prevented any plant species from becoming established except those that were
extremely shade tolerant in the early years and that could germinate either
under or over a litter layer .. Vegetative reproduction was favored in
were
y ,000 s
of rose were recorded in 1981. Hoth
1983--1984 winter.. This site had not changed on
1 to 1983.
was not clear why there were so few spruce and no birch on
it \vas obviously very old.. The present understory was
that it would be difficult for any kinds of seeds to
to germinate and become established, a process which requires
y
soil
and sunlight. Since many of the poplars have been broken off part way up
trunk, the mineral soil that their upturned roots usually pro vi de were
not present.. This breaking of stems rather than uprooting implied
destruction when the soils were frozen. A winter windstorm could have broken
these trunks.. The site might have been in a position such that the wind was
stronger here than in other similar stands or it was just in a different
state of maturation or health. Definitely more of these trees had well-
developed heart rot than in any other area we sampled.
Spruce are usually able to invade successional stands as early as the
alder stage. Yet all the spruce in this site were only saplings < 2 m tall.
Possible explanations for the small spruce population included seed shortage
or poor environmental conditions at the stage of maturity when spruce would
normally colonize, Seed sources appear to he available upstream, but perhaps
winds and currents have never b~een favorable for dispersal. Suitable
conditions for germination and establishment might never have occurredc The
authors have no reason to support one hypothesis over the others.
3 was a spruce site near (
was similar to that of a mature balsam
was not done.. Much time was spent exploring this
trying to understand how a poplar site a
spruce site ..
individuals were able to become established in successional
trees since spruce saplings occurred as early as the r
Invading birch, however, were a rare occurrence. Young birch trees
and grew in the soil on the upturned edge of root crowns of
trees. They did not grow in the shaded, vacant hole, but on
soil attached to the roots.. This microsi te provided both mineral soil
more sunlight than the forest floor. Drainage was probably better here
·~.. Ail in the hole where the old tree had been .. In some sites, almost all
uprooted trees had a birch tree growing on them, and birch were found nowhere
else in the stand. (The lack of uprooted trees may be the reason for poor
invasion in site 28.) Birch trees in some sites (site 11, especially) were
growing on pedestals, the original dead tree, providing further evidence
this was how birch invaded sites.
The authors also found one young balsam poplar stem sprouting from
another dead root stump.. This was the only juvenile poplar we have ever
found in the understory of an advanced site. Poplar was very shade
intolerant.
The three dead poplar trees that provided a base for the birch trees
were about 81, 103, and 124 years oldo Poplar that were still living ranged
from 98 years to 164 years of age with most cored trees being near 130
tree was y
'1.-Jas 129 years a Most t o er mature trees were
105 to 115 years of age. hire~ tree at
a rotten center, hence, it was probably much
stems varied from 1 to 5 years of age while young
15 to 22 years of age. All of these young trees were
The ecological significance of this was not clear, but
to nutrient status. The alder may provide a nitrogen rich
nearby plants since it is a nitrogen-fixer~
The site had a cutbank on the east side of the island and comparison of
1951 and 1980 photographs indicates that side of the islard had been eroding
The channel had moved to the west side of the island, which was more
vegetated that the east side. Just upstream from this site was an area
has been logged. It appeared to have been partly logged in 1951, and more so
by 19800
5.3.2.2 Paper Birch -White Spruce
5.3.2.2.1 Site 29
Site 29 was a paper birch -white spruce site near RM 53 below site 22
(E'igure 10). The overstory was dominated by 46% birch and 18% spruce cover ..
Rose and highbush cranberry provided 29 and 36% cover, respectively.
Horsetails, mostly §..g_uisetum arvense, covered over 50% of the ground ..
Bluejoint cover increased between 1981 and 1984, while field horsetail
decreased.. The site was relatively diverse and was very patchy, as was
typical of birch-spruce sites ..
same stems
in
browsable stems/ha high bush
in 1981 ..
The cored birch was almost 1 years old@ The mature
trees were between 100 and 120 years of age8 The oldest tree
1 years with the other specimens' ages near 107 years. The best growth
to occur after individuals were 50 to 70 years old, more or less
was probably the age when a neighbor fell over allowing more to
understory or when this stem broke through the canopyo Poor ring
separation could account for the difference of these ages relative to
hypothesis that spruce enters a stand first then birch. The 170-year old
could be explained similarly to site 24, mature balsam poplaro These
spruce trees might be second or third generation or entered the site after
the birch had entered. The original spruce trees might have died. In fact,
one birch tree was found growing on a spruce log.
This site itself has changed little since 1951 although the
above it has been eroded since then. Significant portions of that shoreline
had been eroded between the 1981 and 1984 visits. Erosion is also apparent
in comparison of 1980 and 1983 aerial photographs. This site had a very
patchy vegetation distribution, which really required more intensive sampling
for an accurate description. However, the information was probably adequate
for comparing sitese Future comparisons of the same site can be made using
permanent transects, thus eliminating a lot of variability encountered with
this study ..
.. 1
were
2).,
by
4, in contrast
CO\Ier birch
es were r near 1
, accounted 1
stems/ha
an
2 cover
s tems/ha
(
~~~ ~~~~)in the 2-4-m, < 4 em two
accounted for 22% cover combined. Other
rose, high bush cr an herr y, r es, de 1' s t and
a
8000 stems/ha in
Rose and highbush cranberry over
0.. ..0-m
oldest white spruce cored was 142 old while
was 132 years. The o~her old spruce ages obtained in 1984 were
131 while those birch were 110,119, 129, and 96 .. errors
in counting rings, especially for birch, and the small
was insufficient to state that one species came be fore the o
Deadfall was abundant in this site, and some of the birch trees were
on a pedestal of a previously fallen tree, where they had germinated the
soil on the backsides of roots.
This site had no obvious changes between 1981 and 1984 visits or
1980 and 1983 aerial photographs~ It was on the west of channelized
portion of the river.
ca
71
mature trees .. came in
birch trees more at once
the birch trees are old enough,
is might depend on health of i
of crown opeA1ings.. The development of
by its neighbors. For instance, most spruce trees
during their first 30 years, probably suppressed by the
Site 4 had no apparent vegetation changes since 1951.. The
on
ae al photographs had mature vegetation there already.. However,
intermediate anct mature vegetation occurred just east of it across a sloughe
Between 1951 and 1980, this vegetation was eliminated and bare soi 1 (or
st bare) became available for colonization again, or perhaps
secondary succession. The whole island might have been eroded away then
reformed, but based on the constant shape, the elimination of the developed
vegetation seemed a better hypothesis.
The river also eroded a sand bar upstream between 1980 and 1983. More
water was cutting through the slough adjacent to site 4, making it boat~ble
in 1984 where it was not in 1981. The slough had more water, but did not
appear wider than in 1980 (photographs) or 1981 (first visit)o
can
easiest to d
ec tr
as
represents a stage in the
succession is a continuous change, however,
classified to discuss them similarly to vegetation
spectrum. A time line in Figure 15 summarizes
may be present and the earliest we feel certain species
on a "permanent" basis.
t
or
The model ~an be interpreted in either of two ways. One is to
enter
a on the surface of the Susitna floodplain, be it water, bare land, or
vegetated land. Locate this type of "land" in the model and this is your
starting point. The flow lines from that compartment indicate what san
happen to that point and where possible, how long it may take or the
bility of a change. The other method of interpretation is to estimate
percentage of the floodplain is in each compartment, initiate disturbances
such as flooding, and follow changes that occur in the compartments. A more
sophisticated model should incorporate age structures within each compartment
to handle the cycling problem to be discussed later. However, the simplified
version presented here is sufficient to understand the basics of vegetation
succession along the Susitna River.
The first two stages, water and bare ground, are physical locations that
are either still under water or have less than 2% vegetation cover. Whether
something is under water or not obviously depends on the water level,
to assume to
1 at
1980 aerial were
temb er 1983 photographs a was
summer which is about 23,000 cfs ~ The
to conceptualize long-term succession as
floods, ice effects, and animals, rather
associated with seasonal water fluctuations.
by
2% level of vegetation cover is being used as the lower
ve on since this seems to be a minimal level for observing
a
and is what is using for the Alaska vegetation classification
Many of the early successional types had approximately 8-10% cover
we first visited them.. Sites with only first-year seedlings <2%
cover and appeared unvegetated from a passing boat.
Each of the vegetation stages has already been described as have
histories of our sites as far as we have been able to determine or
hypothesize. This information has been synthesized to create the following
model.
6.2 Early Successional Stages
6.2.1 Colonization and Seed Dispersal
Initial colonization of a site depends on availability of sever3l
factors: land to be colonized, viable seeds, and suitable environmental
conditions for germination and establishment. The availability of new land
for colonization would depend on lower flows for a year or peri0d of years,
degradation of the river, local deposition on a bar or formation of a gravel
to
the river a area ..
in equilibrium, redistribution of sediment
to provide new area for colonization
successionally Lower flows for a few years
established, but when flows returned to normal, this
not be able to survive or to advance successionally (unless the
in the meantime or some other compensating event has
flood stages, vegetation would slow flow over islands
to settle, which would further elevate the islands.
Viable seed may be available from any plant species at certain
growing season.. We will assume that seed or other propagules from
non-floodplain species may arrive and germinate, but may not survive the
conditions.. Hence, we will emphasize propagules of balsam poplar, feltleaf
wi ow (and other wi 11 ows to a lesser ,_:xtent) , horsetail, alder, white
spruce, and paper birch. Life histories of these species have already been
discussed, but we will summarize the important features of their seed
dispersal, germination, and establishment as related to early colonization$
Alder, birch, and spruce all disperse seeds in fall and throughout
winter.. Alder seems to invade where poplar, willow, and horsetail have
beco~e established. If the site is available for colonization in the spring,
alder seeds probably would not r~ach the site until the following year after
the fall seed crop. Occasionally we have seen a birch or spruce juvenile in
an early site, but these do not usually survive probably because of heat~
disturbances, and low soil fertility and moisture.
Balsam poplar and feltleaf willow are woody species that establish
initially~ Both produce abundant, nondormant seed which is dispersed in the
) water.,
only a 2 to 4
for germination and ear
is probably by water since line of
occur high water marks where the water elevations
constant before receding. On some islands, these linear
se s
mature, but on others a more random distribution develops.
tter situation may result from shallow, gentle flooding of
rather than just the edges, or it could result from repeated
various angles and differential survival of individualsG
as
Wind is important for carrying seeds to the water, but deposition on
barren sites is by water. Otherwise, newly established seedlings would be
found more toward the centers of islands.. These sites usually experience
drought after waters recede, and plant establishment is difficult e Wind
deposition is considered an unlikely mechanism relative to sheet overflows
Moisture during establishment is extremely important. Both poplar
~nllow can develop long roots to maintain access to soil moisture0 Poplar
roots appear to elongate more rapidly than those of the willow.. The
sandy sites are dominated by balsam poplar, and few other species seem to
survive there initially.. Other species are more important on sites with
finer textures and higher soil moisture. Reproducing poplars ou tn urn be r
willows on the floodplain and seem to produce more catkins per individual
because of the tree's size.. This results in more seed sexuelly.. Poplar
also occur across a broader spectrum of sites than willowe
Spring seed dispersal appears to coincide with spring floods. As flood
waters recede, a concentration of seeds is left, and many of them germinate
contac
roots
s 1 moisture" There young
y
occur later in the summer, depending on flood
to
duration., Hence, seedling establishment depends on water
during spring seed dis rsal then during late summer., Usua Y
July and Augus~. water levels are higher than average May and
water levels; therefore, colonization may not occur each year$ This seems to
with our observations since we have not observed any 2 to old
The new island near site 17 was probably formed under unusual
circumstances, and we observed juveniles on it in 1984., We observed no
seedlings on any sites in 1981, partly because our first visits were in June9
too early for seedlings; and our last visits were after the summer floods,
which would have destroyed spring seedlings.
Horsetail occurs most abundantly on silt deposits and close to island
edges, whtch may be correlated with high soil moisture levels.. These plants
may grow either from fragments washed downstream or from spores ..
horsetail gametophyte is a small inconspicuous plant that develops from
spores produced by the conspicuous sporophyte form. We have not found any
horsetail plants that were just established; therefore, we don't know how it
colonizes new sites. Searches of the literature and inquiries of other
vegetation ecologists in the state have yielded no information on how
horsetail colonizes bare soils in this study areao Spores of some horsetail
species are often produced in cones, dispersed early in the growing season,
and germinate readily on moist soils. This prothallus lives for a few weeks,
produces male and female gametophyte which fuse and develop into another
sporophyte generation.
77
, or
to any barren area, and can germinate
ronmental conditions, especially available soil
which species survivee This natural selection
some species can not survive such conditions
result from competitive interactions among the specieso
may be a e to survive slightly better, but it then slowly
resources until it dominates and the other species are suppressed
Given different conditions, another species may dominate.
can, or
The concept that all species may be available and begin col on iz in g
available sites is based on several observations and assumptionso An island
established between 1981 and 1983 near the confluence of the Chulitna
had all three species present in 1984. The island probably formed during the
high flows in late summer 1981 or possibly during breakup 1982. Both poplar
and willow individuals were 2 to 3 years old in 1984. The surface soils were
medium textured for this ecosystem, consisting of fine sands and .. It
represented typical soil textures rather than an extreme texture such as
cobbles or fine silt. There were microsites on the island where some species
were growing more abundantly than other species due either to environmental
conditions or to initial differences in seed distribution among species@
Site 8 ( Figure 13) changed from a horsetail-willow site to a pure
horsetail site between 1981 and 1984 (Figure 14). The willows and poplars
that had been there disappeared 1 hu~ n~w ~@@dling~, ~~pe~ially of poplar had
germinated beneath the horsetail. Site conditions have obviously favored
horsetail. Whether willow could not tolerate the conditions or whether it
This sit~e
soil
a
and
could favored horsetail over willow.
Site 13 has had both willow and horsetail become more
between 1981 and 1984. Its conditions apparently
moss
species. This area has had sediment deposited from ice in recent
instead of being eroded away.
Site 15 was inundated between July 1984 and September 1984,
the horsetail in the lower elevations, but willow survived"
evational differences along the transect are approximately 0 Sm.. The
horsetail was brown and apparently dead when the site was revisited, but
rhizomes may still be alive ..
horsetails' fate.
This site should be revisited to verify
Based on the general successional advancement of sites between 1981 and
1984, the authors believe that the size or type of event that resulted in
early successional sites has not reoccurred during the study per
(1981-1984).. This event could be a flood which eroded some areas and
deposited fresh surfaces elsewhere. No vegetation retrogression occurred on
any of these sites except possibly the flooding of site 15. Many plant
communities in early successional stages developed more ground cover,
including a moss layer.
Environmental conditions may prevent vegetation from advancing to a
later successional stage. Either low soil moisture availability, high water
tables, repeated sedimentation from floods, or other factors may suppress
plant vigor.. These factors would halt biological improvement of site
conditions and invasion of later successional species.. Mortality and
may
or 6 to 15
development
to an uneven structure
more advanced
, a juvenile balsam poplar stand upstream of the
a similar appearance on aerial photographs 1 an
soil contaiued several deposition sequences. Above stems
7 years in 1984e Some individuals were possibly approaching ml5 to
of age when the years that had been buried are considered®
ants on this site seemed to be stressed and unable to advance
successionally. The site does not seem to have advanced and then been wiped
out by a flood or ice jam. No ice scars were observed on any stems, and it
is a much broader area than is usually damaged by ice deposits.. site
stagnated. It is conceivable that this could remain a juvenile poplar
site for many more years unless the river changes course and erodes the
alluvium or eliminates the flooding eventso
Site 1 appears to have been submerged in shallow water during 1951 ..
nee, the authors believe it might have been available for plant
colonization 15 years later (mid 1960's), if not before. This was based on
how close the submerged surface appeared to emerging. This required a big
assumption on the dynamics of the river, and when the site became available,
which makes it a less desirable example than site 25. In 1981, the oldest
poplar individuals averaged 7 years above ground~ These trees were perhaps
10 to 15 years old if buried sterns were counted. Again, the soils showed a
long history of deposition, but with finer textures (more silt and fine sand)
than deposits at site 25. Vegetation ground cover had developed, but
succession seemed somewhat affected by sedimentation compared with that
an ._e .. was some
to
which appears to be stagnated.
Site 2 very near site 1, but is in a of river
\vas or had vegetation not visible on the 1951
uninterrupted to the alder stage since 1951.
at this site favored plant succession in contrast to those at
and 1 ..
Ice jams may remove juvenile vegetation by pushing the soil and plants
J;
rooted in it (Figure 17).. More frequently ice scrapes these individuals,
but in many cases their stems are flexible enough to bend without breaking ..
Sometimes ice jams may push soil and accompanying vegetation into berms. On
the island near Whiskers Creek, site 12, a depression was observed where ice
removed soil and the berm of soil with most plants still intact (Figure
~~
17)~ With age, stems lose their flexibility and are more easily damaged by
ice jams,. The annual ice effects probably slow vegetation succession t
keeping it cycling within the early stages. Even a few stems surviving
ice-scouring promotes vegetation establishment more rapidly than if plants
had to r einv ade bare ground e These stems propagate vegetatively, which
produces cover more quickly than seedlings. During their early years,
vegetatively propagated shoots survive deeper floods better than seedlings
because the shoots are taller, sturdier and have better root systems.
summer may
to "water" stage.. This
also erode gentle slopes, and may occur
small floods or rapidly with a major
nee appears to occur more often to advanced ( )
than to early successional sites$ Early successional sites
sloping, rather than cut banks, and have been relatively
s
many
of
deposited.. One would expect continued deposition near these sites in
near future, although local conditions may change from net deposition to net
erosion many years from now when the vegetation has matured.
Coarse and fine material appear to be distributed f.rom different
causes and are deposited in different locations. Coarse material is eroded
deposited predominantly at lower levels during large summer flo9ds
silts may be redeposited during both large and small summer floods and to
some extent in the backwaters behind ice jams. Poplar seems to occur more on
the sandier sites, which are most extensive below the confluence of the
Susitna and Chulitna Rivers. The Chulitna carries a larger and much coarser
sediment load than the middle Susitna. Velocities slow below the confluence,
and much sand and gravel is deposited in the complex of bars opposite
Talkeetna, although much is still available for deposition further
downstream e This sediment load, combined with an apparent change in
gradient, produces the wide floodplain and sandy sites suitable for balsam
poplar below the confluence~
to
cover .. , most are not te
with staging are summer
are at an o The are
of snow, except in areas.,
cause and cover vegetation ..
snow, plants would be subjected to
between below-and above-ground
Roots respire even winter and
to survival.. There are probably tolerance among
ec s which might account for in survival to
6.3 Intermediate Successional Stages
The intermediate vegetation successional stages studied
immature balsam poplar. General description of these sites
been presented. Initially, alder seemed to grow more rapidly
balsam poplar or willow$ A 5-year old alder would be about 1.5 m tall
a 5-year old poplar or willow would be only 0.5 m Once a
started advancing successionally, it had potential of reaching the al r
stage in to 20 years.. It is uncertain whether alder grew more rapidly
inherently or whether the other two species' growth rates were
browsing or other conditions. Since alder is a nitrogen-fixing
can growth better than poplar and willow in these nutrient-poor
by
' it
Given
that early successional sites could cycle within themselves for 30 years or
15), a er v etation
15 (very earliest, more
became available colonization$ Early
continued cycling until the river
or decades ..
to
Young alder sites seemed to be flooded at least every
by the recent silt deposits at site 28 below Montana
in
as
older sites such as sites 2 and 19, have almost complete litter
cover and appeared undisturbed, as indicated by the litter and excellent
blue joint cover.. The closed alder canopy limited reproduction to shade
tolerant species. Poplar is very shade intolerant, so it is unab to
reproduce beneath alder or other later vegetation stages., The shade also
limited browse production of the understory, which was associated with low
shrub species or young treeso
These sites were dominated by alder probably until the poplar in the
canopy became 30 to 50 years old above ground, depending on growth rateso
Alder was still important beneath the canopy in these immature balsam
poplar sites, but these alder stems were second growth, usually 20 to 30
years old, whereas the dominant poplars were 40-50 years old and originated
in the early successional stages. At this stage, poplar usually grew better
than alder, whereas alder grew more rapidly than poplar in earlier years of
the succession.. This resulted from reduced browsing because of plant size
and increased soil nitrogen from the alder. Except for the age and species
structure of the overstoryt both alder and immature balsam poplar sites were
very similar ..
root
no"':
sites may
was
structure
stems&
stem was , new
broken, new sprouts
stem. Hence, a site with
stems. mean age stems v1as
All stems this the way the ice
the may not have enough momentum to cross the
That seemed to have happened by site 12 near Whiskers
time vegetation on a site has reached
trees, and grasses have well-developed roots, increasing
to scouring .. Hence, ice effects (aside from trunk scars), are
to cycling age structure within the alder stage and to
erosiono Ice affects alder and immature balsam poplar
that ice jams would have to be much larger to knock down
cut
in immature balsam poplar stages. However, ice scars on these trees
are common, indicating that large jams have occurred.
Beaver occasionally remove select poplar trees om these sites in
preference to alder. This may change the age and species structure
canopy. enough poplar are removed, it could set succession back to
alder stage, which has too dense a canopy for poplar reproduction. This
would probably cycle within itself until either some catastrophe, a
flood or ice jam, opened the s e or t canopy thinned by death of
individuals so other could invade. If conditions are
develops in alder stands. If undisturbed, spruce should Birch may
roots
have not observed
study areas that are dominated by
occurs in many other northern in
Alaska they are underlain by permafrosto
have few birch-spruce stands, if any.
A more likely result of beaver activity compared to the pre ous
is that the balsam poplar canopy would be thinned, and
continue except that a more open canopy would be presentG This would
a more productive understory. Site 10 appears to have reduced
between 1981 and 1984 because of beaverc
6o4 Late Successional Stages
Late stages consist of mature and decadent balsam poplar, transitional
balsam poplar -white spruce, and paper birch -white spruce0 Although paper
birch -white spruce is the oldest forest type that we have sampled, it is
usually considered successional to other types in other environments. The
authors have observed evidence of it being self-reproducing, so it could be
considered a flood disclimax.. Mature poplar stands ,1ay develop as early as
70 years after island stabilization, but are probably the dominant stage
90-160 years after stabilization (Figure 15). Birch-spruce types probably
dominate from year 200 to year 300 or more.
With age, individual balsam poplar trees and understory alder mature and
die, allowing sunlight to reach the lower levels and encouraging rose and
high bush cranberry growth in the low shrub layer. These are productive
browse sites ..
are mature
the ages of stems in
stages are similar., young stems
alder stage do not survive to es 0
, spruce in the immature balsam poplar stage seem to
ages the mature and decadent balsam poplar stanC.s are
Nanson and Beach (1977) have also observed this same
Columbia.. Apparently, either site conditions are not
in the alder stage or else the area is still disturbed too much for
.. Spruce is probably relatively intolerant of sedimentation and
oo ding , compared with balsam poplar.. Because of its shade
may establish in any of the stages at any time, resulting in an uneven
structure.
As large balsam poplar trees die and are uprooted, the soil on the
backside of the upturned roots provide a suitable location for birch seedling
establishment e There is mineral soil and more sunlight in these microsites
than is available underneath the dense shrub canopy.
The usual successional sequence is from balsam poplar to birch-sprucet
which eventually dominate the overstory. There appears to be a discontinuity
in the late successional stages, since no real transitional stands between
poplar-spruce and birch-spruce have been found. Perhaps a catastrophe, such
as a major flood event l) or a downcutting of the river has occurred in the
last 200 years or more that did not affect the sites that are nol,..r
birch-spruce, but which did affect all sites younger than that. There has
that could occur mature
to selectively remove the
have cut down large trees ( 17).,
birch from becoming established for lack on
Cr~:ceivably, sites affected by beaver could a
site sine~ ~p~uce is more shade tolerant. It is not
composition of this type site would be, but it would probably
relatively little browse.
the birch-spruce stage is reached, it seems to be self-reproducing,
at on a short term basis. As trees die, openings in the canopy allow
trees to grow.. Larger car:opy openings may allow shrubs to dominate
that site" Young birch trees are frequently browsed, as are ro.se and
high bush cranberry. This type of vegetation cycling within patches was
particularly evident in site 4.
Several areas of birch-spruce forest have also been logged, and are
currently in a shrub stage .. Birch reproduction appears sufficient to
eventually develop a birch-spruce stando However~ there are many birch stems
tall enough for browse, even in a relatively hard winter with deep snows.
As birch-spruce cycles within itself, moss may develop on the forest
floor, insulating the soils. This could cause soils to become too cold for
birch, and the site could progress to a white or bl3ck spruce stageo This
has never been observed along portions of the floodplain studied0 However,
while digging the soil pit in stand 4 in early June 1981, ice lenses were
-Jiscovered near the surface., Further away from the river, especially
trees
are
on very
dense
terraces
mature
would take root
to
if
dominate the
understory at
the mineral on
would probably have changed to
over because soil
this still open to speculation.
to ,000 cfs
3~000 to
at Gold Cre
1984c,
10,000 cfs rangeo
summer
(mean ann ua 1
the water levels to correspond to
under natural conditions and 30,000 cfs with
could as as soiooo cfs with project.
levels may encase vegetation middle river .
melt rather than forming major jams with
Project operation would greatly reduce nat ur
throughout the year.
7 1 Geomorphology
7.1 1 Middle River
oj ect operation would have the effect of greatly reducing
fluctuations throughout the year. Summer flood events would be
ood
a
at
Ice is
f w
severity and frequency. High-flow events would only be notable the
middle river if extreme flooding upstream occurred when reservoirs were
nearly full. Some excess from the reservoirs might then cause
normal flows in the middle river.
No bedload sediments would reach the middle river from the
since they would trapped in the reservoirs. ts
to
river, but they would too
the may stop any may
occurring. The riverbed is expected to an armor
sediments are removed from bedo A small amount scour occur
of dams as fine materials are removedo is
degradation will not exceed a proximately one foot, on e aver e
( 1985). Due to the more uniform flows, the middle
a better defined, narrower channel. Some vegetative
occur upstream of the maximum ice front progression, which
to between RM 123 and 137. Scour may result in a slightly
de h at given discharges.. Expected morphological changes are shown
3~
The upper 15 to 28 miles (depending on the year) of the middle river
(above RM 123 to 126) would no longer develop a winter ice cover
with-project. Even where the ice cover does form downstream from there, a
slow spring meltout is expected to occur rather than a normal breakup
drive.. The potential for ice jamming and related flooding would be
eliminated or reduced and, therefore, channel or bank ice scour would also
be expected to be reduced.
7.1.2 Lower River
Due to a lowering of peak annual flows from the middle river, long term
aggradation is likely to occur in the first several miles of the lower river
below the Susitna-Chulitna confluence. The delta of the Chulitna River would
extend further toward the east bank of the Susitna River. However,
a
river
91
e~vent ua y
198·4) ..
by high-flow events,
in the Chulitna or
ve
t a
result 'expected to be a so
floodplain, decreasing number of su .......... "' ... ., .......
cover. ·Expected with-project morphological h
in Table 3 (R & M Consultants, Inc. 1982).
sediment contri.bution from the middle would
during extreme high-flow events:. The Chulitna
the major contributors of bedload sediments at
thus continue to have the major i.nfluence on
and morphology (R & M Consultants, Inc. 1982).
r
processes in the lower ri ve:r would remain nearly same,
higher stage due to higher project winter flows and
ig ht thickening of the ice cover. 1'h,e river would melt out
ver
than usual, with no breaku~ drive~ Ice processes would continue to
a lesser effect on river morphology.
7 .. 2 Vegetation
The l{:>wer summer flcMs 'will have these major fects: (1) more new land
will be available for possible colonization and (2) soil moisture levels will
be drter, and (3) water levels will fluctuate less. The lower of
ting veget.::1 t ion s to be :related to flows between the aver e
(
summer
) mean
e ms r
to
, but than 10%
summer ows,
land surface
natural
, or at least would not
events.
( )
by
factors may event or slow colonizat n w h t
......... ,.J."._ ..... : ( 1) unsuitable substrate and ( 2) poor conditions
of vegetation. Most eventual
becomes established on silty to sandy sites. Cobbly
colonized by dryas plants, and may eventually acquire
to support other vegetation. If these sites do not
to
)
or
ojec
sediment, they may retain stunted vegetation for 30 years or more
textured material will be assumed to be an acceptable substrate for
colonization, while cobbly areas may take considerably longer to develop
horsetail, balsam poplar, and willow sites that have been described
report, or may develop different v~getation.
Current vegetation establishment seems to depend on water levels
sp ng seed spersal to provide ( 1) the dispersing mechanism (2)
adequate moisture for germination and early
adequate rai all June, it is pos ble
establishmento
at vegetation may
established initially only near the June water line.
area
summer water
( 1) vegetation and (2)
waterline to the area between
observations seem to indicate that new
co ze a a va able surfaces each year anyway o The lo\ver
delay the initial establishment of vegetation, but
su trate has a suitable texture, the new sites will probably
based on the summer flowso
water levelst however, may cover the surfaces that just
for colonization. Summer floods are usually of relatively
and still permit some aeration of the soils, providing the water
not
moving and not stationary e In contrast, ice may exist on the water
in winter and prevent movement of air between the below-above-
ground atmospheres for several months of the winter. The plants are dormant,
but roots are still respiringo If the plants are only partially covered
, the portion aoove the ice may provide access for the roots to the above-
gr0und atmosphere for aeration. If the plant is completely covered, as might
occur with newly established individuals, no such escape exists and the
treatment is much harsher. This could become the limiting factor to
vegetation establishment and development. Existing vegetation will probably
tolerate the treatment, but new seedlings will have a difficult time becoming
established.
Some invasion may occur at lower levels than the existing vegetation by
vegetative propagation, but this would probably be minor. Winter water and
ice levels may become the lower limit of vegetation, leaving a strip between
sumrne:r water
....... e in the
new vegetation would
water or ice level with
to
of the ice front but below the dam, and summer water
be similar during project operationo Hence, this area
av e for colonization, which would be slow because of
along this stretch of the river.
thout the flood pulses of the present system, vegetation
ably advance unhindered .. To see the effect this would have on
, one could use Figure 15 and see how things change with t
Early successional sites would be available for browse probably from
5 or 7 to years 13 or 15.. Alder and balsam poplar would dominate
next 45 years or so, with relati\~ly little browse in most cases. 60
the shrub understory of the mature balsam poplar and later stages would have
developed with the rose and highbush cranberry browse.. Young paper
trees would probably become available browse by year 100 .. The number of
available browse twigs in each of these stages was already depicted
numerically in Table 6.
7.3 Potential Mitigation Measures
Several approaches could be taken to improve moose browse production.,
The most successful would probably be logging of mature paper birch -white
spruce sites. Existing logged areas produce abundant birch browse as well as
sprouts or
areas browsable height within 5 to 7
winter (OQS m snow depth) and 10 to 20 a
9 weather, and competition from other
cranberry are present in these sites right
for browse at that timee
could also be used, although no examples have
a
on
river,. The nature of riparian habitats genera y prec s
extens e natural fires .. A prescribed fire would require the nor
for fire control.. Burning would release nutrients to
at would not occur with logging.. No commercial product results from
, whereas logging produces marketable timber.
Some of the new land surface available in the summer, but flooded in the
, might be colonized if the transition from pre-project to with-project
conditions were accomplished gradually.. If the summer water levels were
lowered somewhat to make new areas available for colonization, and the
levels increased a small amount also, the new vegetation might be able to
withstand the first winters. By the time the winter flows reached their
normal with-project flows 1 the vegetation might be large enough to withstand
the flooding. This would depend on the slope of the terrain and the height
of the plant.. This may not be considered a viable mitigation technique
because it requires regulating flows for a purpose other than power
production ..
8
ta lo, J.. 1 on ic
ms
mstr ong,
J .. R.
W.. 1 Oxygen diffusion from
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W 1982.. Wa te ogged so s
Environment and plant ecology.
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2nd
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etatio :175-185.
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578 pp.
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Environmental and successional relationships
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sa
The Canadian Field-Naturalist 93:77-790
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Journal of Forest Research 13:903-913.
1
1 .. 5 0
119 0 ..
19 1 0 .. 00153
0.00147
0 .. 00105
42 0 .. 00073
0 0 .. 00030
Split
braid.
west valley
occupy east
Sing channel
occasional islands ..
Transition from split
Occasionally bounded by
through the confluence with
TaJ keetna Rivers.
Braided with occasional
Combined patterns:
braided, fJoodplai n
with
distributary
about RM 205
Is
110 Portage
McKenzie Creek
5 l Creek
Slough
10 Gash Creek
RH 110.0 Creek
17 Whiskers Creek
}
96
86
14 54
10
7
B
13
9 18 45
5 13
size is sh:>~·Tn as n 1 &; ~ n 5 Q, ~nn Dca 11 , are sJ.zes r.tt t--ThJ.ch Jf., 50, ;=.n~ ~11
of the hed ~~terinl narticlPs are ~iner.
zes can divide~ intn
-0.06d ~ to 2.0 MM,
~ 2~0 ~~ 6~-~ ~~,
Cobble -E4o0 1'!'11"'1 to 2 .. 0 rM.
1
cover on y successional s on
lain i ver, summer 1
es
Vegetation by Species or Genus
Eguisetum variegatum
u1us balsamifera
Salix alaxensis
Salix novae-angliae
Salix arbusculoides
Salix sp ..
Astragalus sp ..
Hedysarum sp.
Calamagrostis canadensis
Eriophorum sp ..
Scirpus sp.
Alnus tenuifo1ia
Alnus sinuata
Artemisia te1esii
Nephroma sp.
Variegated horsetail
Balsam poplar
Feltleaf willow
Tall blueberry willow
Little tree willow
Willow
t·1i 1 k-vetch
Sweet-vetch
Bluejoi nt
Cottongrass
Bu11rush
Thinleaf alder
Sitka alder
Wormwood
Nephroma
2
13
+
1
+
+
4
+
8
. 25
8
4
1
+
+
+
+
+
+
+
+
+
+
+
a/ Early successional stands were numbers 1, 5, 6, 8, 9, 13~ 14, 15,
20, 21, 22, and 25 (Figure 5). Number of transects sampled was 42.
t
contract to
sco Susitna Jo
1
e 4 .. Density (stems/ha) of woody
Sus i River, summer 1
Balsam poplar
Sitka a·lder
Feltleaf willow
es in
novae-angliae Tall blueberry w111ow
arcticus Arctic willow
sp. Willow·
1
< $4 m Tall
38865
8
4929
1762
305
45865
i successi
.4 ... 2 m 1 < 4 em > 4 em
. 1103 40
643 40
8643
1850 135
48
--···•»
12287 215
y successional stands were numbers 1, 5, 6, 8, 9, 13, 14, 15, 20, 21, 22, and 25 (Figure 5).
sampl was 42. Browsable stems were those taller than .4 m but with dbh < 4 em.
> m 1
e 5 . sties ies in y on
River·, summer 1981
(em) (em) . (em)
alaxensis Feltleaf willow 60 25 18 5 2
novae-angliae Tall blueberry willow 18 12 3 2
spp. Willow 68 31 25 4 2 ')
4-
sinuata Sitka alder 186 163 1 5 2 12
tenuifolia Thinleaf alaer 154 100 87 3 2
ba 1 sami fera Balsam poplar 44 24 19 6 2
Early successional stands were numbers 1, 5 t ~' 8, 9, 1319 14t 15, 20, 21 ~ 22, and 25 ( 5) ..
transects sampled was 42.
Pi Only 62 observations for height ..
e 6 g means successi
All numbers been
g i n Stage Density Total t gs A ailab e
ecies stems/ha Twigs/stem . Browsed igs/h
ly Successional Stages
lsam poplar 1500 2 .. 7 4 41
ltleaf willow 4300 4.7 76 145
Ald
lsam poplar 3700 3.5 5 71
ltleaf willow 1200 4Q6 50 5300
Immature Balsam Poplar
11 blueberry willow 170 2ol 34 7
Prickly rose 6000 2 .. 5 3 135
High bush cranberry 21000 1 e 1 19 12SOO
Mature and Decadent Balsam Poplar
Prickly rose 16300 6 .. 0 41 98('
High bush cranberry 11300 5 .. 6 29 63 0
per Birch-White Spruce
Paper birch 400 7 .. 8 9 34
Tall blueberry willow 100 4 .. 8 46 0
Prickly rose 3400 4 .. 7 31 16000
Highbush cranberry 400 1 .. 8 28 2
b 7° Percent cover for stands dominated by rsetai o
ownstream floodplain of Susitna River, summer 19 1
X
CANADENSIS
\f•E GRASSES 1. 0. 3 2-; 0
\ 41.. 5.5 5'36.6
I LOW SHRUBS 4~ 1.6 45~6
f TREE~ .. · , . · . ;.:.·~::~;;t~:· .. · ·.·.· <(:~~:.--{.:.·.-:·:::'' ,,.. .:<:;_~:~n:> ·. 2 •-:·_ . 0. ~·. ,: :~ ~ .. s·. ~ .
! TOTAL· VEGETATION · ·: .. ··.,-·:.~:"Y'·: · ' ..... .*.'· _;.-. · 46 •·. . · 5 .,;;, ... ; ... ·· · ;:s49 • ..; .. :·
\ ----""':~--,~:....:.:...,.:...·~~~:..:.~-~...:~·~:,.:__ ..... ~ __ ...:..:...~...:.---~--.::..----~------":"~~---··-------:..:~.;·~--·.;.:j'' ..
I
11
,. " .... ~ ... ~ ... ·::---~ .... -
I e I
9.. nsity (st s/ha.) o wood spe i s i s
setail on do stream floo p ai f u i
r 19 1 ..
c. nt c
r on do\tln
r 1 1
2
v r f r stands omin t
tream fl plai of
b j u. v
itna
1 1
b
ristics o
lsam p
iv :r" summer~l
11
y p ies i s
down t e m
... -·""··-~.,---· ... --··--· ~ ... -.. .,.::.~:.. .. .d,.;.4_:·_. -.......... ··--"'"· _ .... ·-~
1
( stems I ) o f wood y s p e c i e s i n s tan d s d om i n a ted
le balsam poplar on downstream floodplain of
r, summer 1981 ..
------------------------~------------------------· 2
·-·----·-·-----·---· ·---·
-------~-------------~~----------~---------~~ii--~-----------~.
.u 53 . .
--.. 2
1
1
~~~~~~~~~~~~~~~-~~~~~~~-~~~-~-~----~-~---~~~-~-~~~~~~~-~~~~~-~
. --~------------------
le 1
on
:.·lt··
115
rc n cover for stands dominat by
ownstream loodplain of Susitna Riv
0.2
• ~ o.
0.2
0.6
0.7
-
•
1.2
0.3
II'
1.:3
0.3
3 .. 7
4 .. 0
wil
19
116
le 14.. haracteristics o woody species in
fel le f llow on downstream loodp ai
er summer 1981 .. na
( st.ems/
llow
981a
) f 00
n downs
~~~~~~~~~~~~~~~~~~~~~~---~-~--~--~~~~~~~ --... ------... --·-~·~--·-----..
---~-" .-
al
, summer
angustifolium
balsamifera ~~..;;..;;...sia tiles1i
x alaxensis ~~ Salix novae-angliae
Salix sp.
Stellaria sp ..
1 obTUin 1 ati fo 1 i um
Rosa acicularis
R'16'es spp.
Hedysarum sp.
Rubus arcticus
Rubus idaeus
Trientalis .......;;.;..__,..1,....;.........;...,
Gal1um sp ..
Poa sp ..
were numbers 2, 19,
samp1 was 20.
Bl nt
Thinleaf der
Sitka al
s
Highbush cranberry
Fireweed
Balsam poplar
Wormwood
Feltl willow
Tall blueberry wi11ow
Willow
Starwo,rt
Dwarf fireweed
Prickly rose
Currant
Sweet-vetch
Nagoonberry
Raspberry
Arctic starflower
Bedstraw
uegrass
, and 27 (Figure 5)~
a
Number
+
6
3
1
3
13
3
5
+
+
+
+
+
+
+
+
+
+
e 1 .. Oens1ty (stems/ha) of 1es al s
< .4 m Tall .4 -2 m < 4 em > em > 4 m
Popu 1 us ba 1 sami fer a Balsam poplar 861 1
A 1 nus tenu i fo 1 i a Thinleaf alder . 483 1 633
Alnus sinuata Sitka alder 133 Jl
Salix alaxensis Fe 1 tleaf willow 617 2517 167 1
Picea· glauca White spruce 17 17
Echino2anax horridum Devil 11 S club 133
r~ubus i daeus Raspberry 967 200
Rosa acicu1ar1s PricklY rose 517 117
Viburnum edule U1ghbush cranberry 467
Salix novae-angl1ae Tall blueberry w111ow 83
Ribes triste American red currant 1133
Salix sp:-Willow . 783 --t.
--"
1 5384 6417 1250 11 1
stands were numbers 2. 19, 23, and 27 (Figure 5) .. Number of sampl was were
taller than .4 m but wtth dbh < 4 em.
I • 11
i
7.9
7.0
3.9
4e9
467
ons dbh.
ons for age ..
ons for dbh.,
(em)
7.2
(.3
3 .. 4
4&6
5 .. 0
19
17
13
11
2
2
5
4
4
4
a/
cover in
ain, summer
Snecies or Genus
s balsamifera
tenuifolia
sinuata
~alamagrosti~ canadensis
Viburnum edule
Artemisia tilesii
Heracleum lanatum
Mertensia paniculata
Rosa acicu1aris
Picea glauca
Salix novae-angliae
P,xrola secunda
Pyrola sp. ..
Rubus idaeus
Sanguisorba stipulata
Galium sp ..
Matteuccia struthiopteris
StreEto2us amElexicaulis
lsam r
Balsam poplar
Thin1eaf alder
Sitka alder·
Bluejoint
Highbush cranberry
Wormwood
Cow parsnip
Ta 11 b 1 u e be 11
Prickly rose
White spruce
Tall blueberry willow
One-sided wintergreen
Wintergreen
Raspberry
Sitka burnet
Bedstraw
Ostrich fern
Cucumber-root
Immature balsam poplar stands were numbers 10, 12, and 26
Number of transects sampled was 18.
.. -+
9
+
6
62
8
21
3
3
1
1
1
+
+
+
+
+
+
+
+
+
(Figure 5).
e . Densi (stems/ha) pf in sam ar
< .. 4 m Tall .4 -2m 1 < 4 em > 4 em > 4 m 1
Populus balsamifera Balsam poplar 19 9
Alnus tenulfolia Thinleaf alder 74 1 1 1
Alnus sinuata Sitka alder 907 19·
Salix a1axensis Feltleaf alder 352
Salix SPo Willow 148
Picea glauca White spruce 31
Rubus idaeus Raspberry 1185
Rosa-acicularis Prickly rose 1037 1519
Viburnum edule Highbush cranberry 630 463
Sa 1 'i x novae-iu Jl iae Tall blueberry w111ow 31
Ribes sp. Currant .759
Total 3685 5241 2537 675 1 1
Immature balsam poplar stands were numbers 10, 12, and 26 (Figure 5) .. Number of transects was 18. e
stems were those taller than .4 m but less than 4 em dbh.
e ~Je Characteri cs of ies 1n
Susitna River~
Height
(em)
Salix novae-~ngliae "· fe1t1eaf willow 125 53 45 9
Ribes sp. Currant 48 35 ' J
Rubus idaeus Raspberry 35 29 1
Betula papyrifera Paper birch 102 25 22
Picea glauca White spruce 10 10 1 2
Alnus sinuata Sitka alder 181 153 1 8
Alnus tenuifolia Th1nleaf alder 139 73 6
Populus balsamifera Balsam poplar 182 63 39 15
Rosa acicularis Prickly rose 56 40 32 2
Viburnum edule H1ghbush cranberry 94 69 51 5
a/ Immature balsam poplar stands were numbers 10. 12, and 26 (Figure 5). Number of
~ No observations for age.
£1 Only 13 Qbservat1ons for age.
Only 31 observations for age.
6 8
1
1
6
7
6
6
6 8
6
6 2
was 18.
Table J.J.. Characteristics
downstream oodplain
Populus balsamifera
Alnus tenuifo11a
Alnus sinuata
Betula papyrifera
Picea glauca
Balsam poplar
Thinleaf alder
Sitka alder
Paper b1rch
White spruce
i
1
Mean
Height
(m)
17 .. 7
6.6
5 e 1
6 .. 2
2 .. 6
sam
24 .. 8 2
6 .. 9 22 4
8 .. 5 22 5
12 .. 4 4
13 6
a/ Immature balsam poplar stands were numbers 10, 12, and 26 {Figure 5). Number of
sampled was 18 ..
~ Only 35 observations for crown dominance.
fl Only 31 observations for age.
d/ Have 4 observations for age.
~ Have 2 observat1ons for height.
fl No observations for dbh.
I
r·cent cover
Total vegetation
Vegetation by SQecies or Gen~2
Populus balsamifera
Alnus tenuifolia
Ai"iiUS sinuata
Viburnum edule
Rosa acicularis
~magrostis canadensis··
Ribes spp ..
Me~nsia panicu1ata
Echinopana~ horridum
Rubus idaeus
Dryopteris dilatata
Gymnocarpium sp.
Matteuccia struthiopteris
Streptopus amplexicaulis
Picea glauca
Cornus canadensis
Heracleum lanatum
Pyrola sp ..
Jrientalis ~uropaea
&alium sp.
1
sam
Balsam poplar
Thinleaf alder
Sitka a.l der
Highbush cranberry
Prickly rose
Bluejoint
Currant
Tall bluebell
Devil's club
Raspberry
Spinulose shield-fern
O~k-fern
Ostrich fern
Cucumber-root
White spruce
Bunch berry
Cow parsnip
Wintergreen
Arctic starfl ower.
Bedstraw
ar s
+
12
+
41
3
15
12
3
2
4
1
5
7
1
1
+
+
+
+
+
a/ ~1a ture and decadent ba 1 sam poplar stands were numbers 3, 17, 24,
and 28 (Figure 5). Number of transects sampled was 248
Table Characteri 1n
floodplain of Susi ver, summer 1
Mean
Height
(em) (em) (em)
Ribes triste American red currant 29 18 2 ·1 16
Ribes sp .. Currant 50 45 3 7
Rubus idaeus Raspberry 65 45 29 1 7
Alnus sinuata Sitka alder 248 121 9 6
Alnus tenuifolia Thinleaf alder 205 78 53 6 6
Rosa ac1cu1aris Prickly rose 65 43 31 2 6
Viburnum ~dul~ Highbush cranberry 81 45 30 4 6
!I Mature and decadent balsam poplar stands were numbers 3, 17s 24, and 28 {Figure 5). of
sampled was 24.
~ Only 24 observations for age.
Table J~ .. Character·i sties sam
floodplain ~f Susitna
Mean
Height
(em) {em) (em)
Ribes triste American red currant 38 29 18 2 ·1 16
iU bes sp .. Currant 50 45 25 3 7
Rubus idaeus Raspberry 65 45 29 1 7
Alnus sinuata Sitka alder 248 121 87 9 6 8
Alnus tenuifolia Thinleaf alder 205 78 53 6 6
Rosa ac1cular1s Prickly rose 65 43 31 2 6
Viburnum edu1e Highbush cranberry 81 45 30 4 6
a/ Mature and decadent balsam poplar stands were numbers J, 17. 24, and (Fi 5) ..
sampled was 24.
~ Ooly 24 observations for age.
< .. 4 m 1 .. 4 -2 m 1 < 4'cm > > m 1
Balsam poplar
Thin1eaf alder 1 7 14
Sitka alder 111 7 7
White spruce 3 3
Oevi1•s club 14
Raspberry 2184
Prickly rose 1611 1
Highbush cranberry 1722 21833
American red currant 6569
12100 39556 2514 21
N
and decadent balsam poplar stands were numbers 3, 17, 24, and 28 (Figure 5). • -.......!
Number was
e stems were those taller than 0.4 m but with less than 4 em dbh.
e cs
on downstream f1
Populus balsamifera
Alnus tenuifolia
Alnus sinuata
Betula papyrifera
Picea ill~
.Balsam poplar
Thinleaf alder
Sitka alder
Paper.., birch
White spruce
Mean
Height
(m)
26 .. 4
7»1
5 .. 3
14.2
14 .. 0
dbh
(em)
53 .. 2
7 .. 4
16 .. 6
23 .. 6
23 .. 8
Age
98
28
50
63
94
2
5
5
2
3
a/ Mature and decadent balsam poplar stands were numbers 3, 17, 24, and 28 (Figure 5). Number
transects sampled was 24 ..
b/ Only 33 observations for age and 38 for crown dominance.
fl Only 32 observations for age.
Q/ Only 1 observation for crown dominance.
e/ Only 6 observations for age and crown dominance ..
f/ Only 14 observations for age&
shrubs
1 shrubs
Trees
a. in i\
ries
Total vegetation
Vegetation by Species or Genus
Betula a rifera
Picea g
Alnus ~te-n~u~i~folia
~~ s1nuata
Viburnum edule
Ribes spp.,
Rosa acicularis
Cifamagr,ost1 s canadensis
Dryopteris dilatata
Gymnocarpiu~ sp.
Echinopanax horridum
Cornus canadens1s
Mertensia paniculata
Rubus idaeus
Epilobium angustifolium
Epilobium latifolium
Salix novae-angliae
Rubus sp.
Rubus arcticus
Trientalis europaea
1
s on
Paper birch
White spruce
Thinleaf alder
Sitka alder
Highbush cranberry
Currant
Prickly rose
Bluejoint
Spinulose shield-fern
Oak-fern
Devil's club
Bunchberry
Tall bluebell
Raspberry
Fireweed
Dwarf fireweed·
Tall blueberry willow
Bramble
Nagoonberry
Arctic starflower
1
+
18
1
14
12
10 s
19
5
18
7
4
4
"1
1
3
1
+
+
+·
+
+
a/ Birch-spruce stands were numbers 4, 11, and 29 (Figure 5). Number
of transects sampled was 20.
e s in
Height I s
(m)
alder 5 .. 5 6 .. 1 5 6
Si alder 4 .. 3 7.0 5
Paper birch 15.5 .. 2 72 2
White spruce 16 .. 2 • 1 2
were numbers 4, 11, and 29 (Figure 5). Number was
ons for age crown dominance.
e Density (stems/ha) of woody species
< .. 4 m Tall .,4 ... 2 m 1 < 4 em > 4 em > m 1
Alnus tenuifolia Th1n1eaf alder 167 1033
Alnus sinuata Sitka alder 17 117
Betula papyrif~ra Paper birch 50 350 400
Picea glauca White spruce 333 133 143
Echino2anax horridum 0ev11•s club 1183
Rubus idaeus Raspberry 3683 167
Rosa a ularis Prickly rose 16950 1
Viburnum edule Highbush cranberry 167 17050 17217
Salix novae-angliae Tall blueberry willow 20C
SEiraea beauverdiana Beauverd spiraea 100
Ribes sp .. Currant 10367 __;,
Actaea rubra Baneberry 83 (_.,)
J
Salix sp., Willow 467 467
Total 14817 ' 36517 1683
rch-spruce stands \·1ere numbers 4, 11. and 29 (Figure 5) .. Number of sampled was 20 .. were
11er than 0.4 m but less than 4 em dbh ..
b 1 e JO. Characteristics of woody on a n
summer 1981 ..
Mean
Height Length
(em) (em) (em)
Salix ~vae-angliae Tall blueberry willow 112 34 6
Salix spp. Willow 78 33 7
Alnus sinuata Sitka alder ll5 101 62 12
Alnus tenuifolia Thinleaf alder 226 105 83 11
Betula papyrifera Paper birch · 116 66 6
Rosa acicularis Pri.ckly rose 81 49 31 2
Viburnum edule Highbush cranberry 94 49 35 5
Rubus idaeus Raspberry 57 51 24 1
a/ Birch-spruce stands were numbers 4, 11, and 29 (Figure 5) .. Number of transects sampled was
6
6
6
5
6
6
6
1
1
1
5
16
1
1
s
specific es are
is stable and little change in
Creek fan will progress out ·into the Susitna
until equilibrium with the regulated Susitna stage
established.. Perching of the stream mouth is
144 RM 139
Erosion of valley walls and terraces win decrease
dramatically due to the armour layer ..
Reworking of alluvial deposits in the main channel will
continue but at a reduced rate ..
· Main channel form will progress slowly to a more unifor·m ·
sinuous pattern ..
Subchannels may become inactive.
Tributary at RM 144 could become perched. It may not
be able to regrade its coarse bed sediments to meet the
regulated Susitna water level ..
RM 139 to RM 129 .. 5
0 Indian River will continue to extend its alluvial deposits
into the Susitna.. Indian River should easily grade its
bed to meet the regulated Susitna Stage.
Gold Creek gradient is presently very steep as it enters
the Susitna.. The cobble and boulder bed will resist
regrading the bed to meet the regulated Susitna stage.
° Fourth of July Creek gradient is curr·entiy relatively flat
and should easily adjust to the regulated Susitna
valley wal ,
~ILili..AbC dramatically
(
1
main
channels rejoin the
encroachment wi II occur ..
RM 119
of val walls 1 terraces alluviaJ deposits n
reduce dramatically.
RM 128 and 125.5 1 reworking of gravel bed
will continue, but a rfaduced rate.. Main channel
will become more uniform ..
Cobbf~ berms at the side channels and sloughs wil:
control and perhaps block main channel flow from
entering them ..
The river should continue its, preferred and ·stable route
along the west valley wall..
RM 119 to RM 104
No consequential changes in the channel morphology are
expected.
RM 104 to RM 95
Chulitna River will continue to expand and extend its
alluvial deposits.. Decreasing the summer flow magnitude
in the Susitna River will allow the Chulitna to extend
aU uvial deposits to the east and south., This could
induce erosion of the east ban kline towards the railroad.
Increased deposition at the confluence will caus.e
backwater up the Susitn? River. Lateral instability will
continue after the project ..
The Talkeetna River will maintain the ability to create its
channel into the Susitna system. No consequenti
interactions can be foreseen at this time.. . .
RM 95 to RM 61
0 Under post-project conditions, the ban kfuU flood (mean
annual ffood under pre-project conditions) could be
a recurrence interval once
This will
movement
I
• (!I
42
1
cover
inactive ..
flood generated
keetna River, or both,
delay observable chan~1es
It must
either
could mask
several.
.
Delta Island reach is a very complex and unstable
network.. There exists a very broad floodplain
filled with varying channel types.. Project induced
changes in flow and sediment regime realized at this
reach vvill diluted by contribution from tributaries and
the Susitna satisfying its sediment load by reworking
the wide floodplain alluvial deposits.. Basic changes in
the overall channel network are not expected ..
Local changes could occur in the main channel lateral
position but basic channel geometry should remain.
relatively simiJar.. To quantity post project morphology
changes with respect to the natural system would be
extremely difficult, if not impossible ..
RM 0
Effects of the project on river morphology through this
reach of river would be extremeiy difficuft or impossible
to quantify. The dilution effect of major and minor
tributaries as well as the balancing of changes by the
Susitna River system should mask any measurable
changes that could occur as a result of the project for
several decades ..
1 ..
ure ') ' ... :1 L ' 1 1 ' l
Figure 3. Locations of sites 12, 13, 14, 15, 16, 17.
Figure 4. Locdcions of sites 18, 20.
5. Locations of sit s 18, 19.
~ Figure 6 . Locations of sites 25, 26.
i
'j
Figure 7. Locations of sites 27, 28 .
. -·----~~~
Figure \S. Locations of sites 5 ' i)' ' 9, 10.
Figure 9. Locat ons o s tes l, 3' 3 l .
Figure 10. Locations of sites 22, 23 29.
Figure 11.
146
Feltleaf willow plant which has been buried and
regrown.
147
Figure 12. Balsam poplar plant which has been buried. and regrown.
I i 11·1 'I ~ l i I ~[.I' ,. i'! I; Figure lJ. l!orsetaj l site Bin 1981 (left) and 1984 (r]ght). Note the increased size of slough in background a ll d r c d u c e d a 111 o u n"'t o f J ~i 11 d f o r h o r s e t a i l s i t e . ..j::::. co
149
.,....
RElATIVe
PRQ6A61LITV
Of. THIS TYP-(;
. V(;<at;T ATIQN
OCCURRING
EARLY
1
0.-1' 10
IMMATIJR{;!
MATURE~ R~9APfJNT
160 200 .220
FIGURE 15. Time line Indicating vegetation types and major evc;;mt$ during succession the
240
Figure 16. Alder and immature balsam poplar that have been bent
during ice jam slooding, site 12.
Figure 17. Young willows that have b~en scraped by ice, site
12, 1981.
Figure 18. Young willows that have been pushed with the soil
berm by ice, site 12, 1981.
19.
Bed
a a.. wen as· proper substrate-
Mean Summe~
Also· WinteJ
Above-tee