and thus lack sediment input. Vegetation tends to
The use of the Alaska Vegetation Classification
be dominated by slowly growing, evergreen spe-
(AVC) for classification generated a large number
cies that tolerate stressful, low-nutrient condi-
of classes due to changes in the canopy coverage
tions. In addition, the fine-grained deposits can
(open, closed, woodland) of trees and shrubs. In
be extremely ice-rich and are highly susceptible to
many cases, such as for the black spruce types, the
thermokarst. Rocky residual soil in the upland
understory vegetation was similar among the
area of the YMA also lacks active sedimentation,
classes. Similarly, small changes in tree composi-
is thaw stable, and tends to be dominated by black
tion led to generation of a large number of decidu-
spruce.
ous and mixed forest classes. We also created five
The water body classification differentiates
new classes that were not in the AVC due to
numerous characteristics that are ecologically
canopy cover problems, including Closed Spruce
important to invertebrates, fish, and wildlife. In
Tamarack Forest (no closed canopy class existed),
general, rivers are different from lakes, glacial riv-
Mixed Conifer Woodland (no woodland class
ers are rich in sediment whereas nonglacial riv-
with Tamarack), Open Paper BirchQuaking As-
ers have higher humic and tannic compounds,
pen Forest (no open canopy class existed), Closed
shallow water tends to melt earlier and become
Low Shrub BirchEricaceous Shrub (no closed
warmer than deep water, connected lakes allow
class existed), and Lowland SedgeHerb Bog
better fish passage than isolated lakes, and river-
Meadow (needed to recognize herb-rich meadows
ine ponds are prone to flooding and sedimenta-
in infilling ponds).
tion. Only a few of these characteristics were dif-
ferentiated in the final ecotypes (see Ecotypes
Association among ecosystem components
section) to reduce the number of classes. For habi-
Toposequences. The principal foundation for
tat studies, these waterbody types are preserved
ecosystem classification was the survey of ecosys-
in the ITU code in the mapping and can be used
tem components (e.g., topography, geomorphol-
for specific analyses.
ogy, soils, hydrology, permafrost, and vegetation)
Vegetation. Field surveys identified 49 vegeta-
along 11 toposequences and at 131 ground refer-
tion types within the study area (Table 5). During
ence sites (App. B and C). Cross-sectional profiles
mapping, 35 vegetation types, 3 nonvegetated
were constructed to illustrate the relationship
classes (water, barren, partially vegetated), and 10
among geomorphology, hydrology, vegetation,
complex units were recognized (Table 6, Fig. 6 and
and permafrost along the 11 toposequences
7). The complex classes were associated with geo-
(Fig. 822). The toposequences display two-
morphic processes (particularly thermokarst) that
dimensional views of the structure of the litho-
created highly patchy vegetation distributions.
facies that were used as the basis for classifying
E l e v e n vegetation types were not mapped
and mapping geomorphic units. Examples of
because they either were too small in extent or
toposequences from the three ecodistricts (Tanana
could not be differentiated on the aerial photog-
Flats, Tanana Floodplain, and White Mountains,
raphy (denoted by * on Table 1).
see Ecodistricts section) are presented below to
Within the YMA, the dominant vegetation types
illustrate some of the main ecological relation-
included Open Black Spruce Forest, Closed Paper
ships within Fort Wainwright.
BirchQuaking Aspen Forest, Closed Spruce
Within the Tanana Flats Ecodistrict, the geo-
Paper Birch Forest, Closed SprucePaper Birch-
morphology is dominated by deposits of the
Quaking Aspen Forest, and Open SprucePaper
thick (2- to 4-m) silty and ice-rich abandoned-
Birch Forest. Nonforest types were limited in ex-
floodplain cover over gravelly riverbed deposits
tent. Within the Tanana Flats, the dominant veg-
with numerous organic deposits in collapse-scar
etation types included Closed Black Spruce For-
bogs and fens. These have resulted from thaw
est, Open Black Spruce Forest, Open Black
degradation of permafrost (Fig. 915 and 22). This
SpruceTamarack Forest, Closed SprucePaper
permafrost degradation has created some of the
Birch Forest, Closed Low Shrub BirchEricaceous
more unique ecosystems found within the study
Shrub, and Closed Low Scrub. In addition, vari-
area. In areas where thaw degradation is rapid,
ous thermokarst complexes were common. Shrub
birch forests are common on the slightly elevated
and herbaceous types were much more abundant
(1- to 2-m) plateaus adjacent to the fens as a result
on the Tanana Flats. Differences in vegetation
of lowering of the water table and aeration of soils
mostly were due to differences in upland (YMA)
(Fig. 911). The soils associated with the birch for-
and lowland (Tanana Flats) topography.
est have thick (0.5- to 0.8-m) peat layers resulting
18
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