Ecodistricts

Table 10. Continued

Figure 25. Map of ecodistricts within Ft. Wainwright, central Alaska, 1998

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Table 10 (cont'd). Description of the physiography, geomorphology, hydrology, permafrost and vegetation of

ecodistricts and ecosubdistricts mapped within Fort Wainwright, central Alaska, 1998.

An association of retransported deposits on lower slopes, meander riverbed deposits, and meander

Mountains

Lowlands

active and inactive floodplain cover deposits. Permafrost is continuous, except under larger streams.

(cont'd.)

Vegetation is dominated by black spruce and birch forests, low shrubland and tussock tundra on fine-

grained, saturated soils. White sprucebalsam poplar forests are found along floodplains.

FrenchMoose

This area has been greatly affected by eolian deposition adjacent to the Tanana River. The low knob

Creek Lowlands

and swale topography has an association of lowland loess, eolian sand, lowland retransported depos-

its, and organic collapse scar and flat bogs. The area generally is above the Tanana Floodplain, but has

numerous small streams originating in the highlands. Permafrost is nearly continuous; it is absent in

collapse scar bogs, thaw ponds, and ridges of well-drained sand dunes. Black spruce and birch forests,

shrub-tussock meadows, sedgemoss bogs, and aquatic vegetation in shallow thaw ponds are common.

Bedrock with an Alpine climate has repeating

its on the flats can occur on Veneer or Flat Bogs

assemblages of Alpine Rocky Dry Dwarf Scrub

overlying the ice-rich Abandoned Floodplain

and Alpine Rocky Moist Tall and Low Scrub,

Cover Deposits, or more recognizably, on Col-

whereas Abandoned Floodplain Cover Deposits

lapse Scar Bogs and Fens that result from paludi-

are dominated by Lowland Wet Needleleaf For-

fication in pits and ponds as a result of thermal

est, Lowland Wet Broadleaf Forest, and Lowland

degradation of ice-rich permafrost.

Wet Low Scrub. In addition, ecosection maps are

Ecodistricts. Ecodistrict maps were created by

produced at a smaller scale (typically 1:100,000 to

a separate delineation on Landsat satellite imag-

1:250,000) with larger minimum mapping size for

ery based on the recurring patterns of geomorphic

patches; thus many tiny patches would be elimi-

classes with distinctive physiographic characteris-

nated.

tics. Three ecodistricts and 21 ecosubdistricts were

Viewing the geomorphic maps (Fig. 4 and 5) as

delineated within Fort Wainwright (Table 10, Fig.

if they were ecosection maps reveals a close asso-

25). Ecodistricts and ecosubdistricts both use geo-

ciation among groups of ecosections that are hy-

morphology and physiography as the differenti-

drologically linked by surface and groundwater

ating characteristics, but differ in that ecosub-

movement. This water movement affects loss and

districts delineate smaller areas with less variation

accumulation of sediments and nutrients and,

in the composition of the geomorphic assemblages.

thus, greatly affects thermal status and ecosystem

The ecodistricts provide a way of stratifying the

productivity. For example, in the White Mountain

distribution of ecotypes that frequently are con-

Ecodistrict, Weathered Bedrock ecosections on

textually related. For example, Lowland Fen

ridges, Residual Soil ecosections on upper slopes,

Meadow, Lowland Scrub Fen, and Lowland Bog

Lowland Retransported ecosections on lower

Meadow were found almost exclusively on the

slopes, and Headwater Stream ecosections in val-

TananaWood River Flats Ecodistrict because of

ley bottoms all are linked by the downslope

the predominance of ice-rich, fine-grained soils.

movement of water and sediments. The accumu-

Similarly, riverine ecotypes were found predomi-

lation of fine-grained sediments and organic

nantly in the Tanana Floodplain Ecodistrict because

material and increased moisture in valley bottoms

they are associated with flooding and sedimenta-

lead to thermal properties that are conducive to

tion. Alpine ecotypes were limited in distribution

permafrost formation. In the EielsonTanana

to the SteeseWhite Mountain Ecodistrict because

Floodplain Ecodistrict, ecosections on Riverbed,

of the higher topographic relief.

Active- and Inactive-Cover Deposits are linked by

This successive partitioning of the landscape is

the flooding regime and sediment transport of the

useful not only for field sampling, but improves

Tanana River. In the Tanana Flats Ecodistrict,

the reliability of conceptual models of ecosystem

ecosections on Abandoned Floodplain Cover

distribution developed from toposequences. In

Deposit, Alluvial Fan Abandoned Floodplain

turn, the ecodistricts are useful for land manage-

Cover Deposit, and Glaciofluvial Abandoned

ment, because management concerns and objec-

Floodplain Cover Deposit are all linked by hydro-

tives will be different, depending on the predomi-

logic changes during deglaciation in the Holo-

nant geomorphic and vegetation characteristics of

cene. Ecosections associated with organic depos-

the area.

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