APPENDIX A: VEGETATION TYPES ON FT. WAINWRIGHT,
INTERIOR ALASKA
by G. F. Tande
Alaska Natural Heritage Program
Forest vegetation
Upland forest types of the Tanana Flats and the YMA vary from highly produc-
tive aspen (Populus tremuloides), paper birch (Betula papyrifera), and white spruce
(Picea glauca) on south-facing, well-drained slopes, to slow-growing, moss-domi-
nated black spruce (Picea mariana) forests on north-facing slopes, lowlands, and
lower slopes that are generally underlain by permafrost (Viereck et al. 1986).
Highly productive floodplain forests of balsam poplar (Populus balsamifera) and
white spruce occur on recently formed river alluvium where permafrost is absent.
In these riparian situations, young stages of revegetation are dominated by willow
(Salix spp.) and alder (Alnus spp.) thickets, intermediate stages by extensive stands
of balsam poplar, and the later stages by well-developed stands of white spruce
(Viereck 1989).
Black spruce may be the most widespread forest type on the base. Upland black
spruce occupies north slopes at all elevations, and ridgetops and most slopes above
400 m (1200 ft) in elevation (Viereck et al. 1983). It is especially widespread in the
rolling uplands of the YMA where loess deposits are shallow over bedrock.
Lowland black spruce occupies old terraces of the major rivers, small valley bot-
toms, and the lower slopes along small drainages in the uplands. Lowland black
spruce types are wetter, and Sphagnum mosses and Eriophorum vaginatum tussocks
become more abundant in older stands. Also, tamarack (Larix laricina) occurs occa-
sionally along with scattered paper birch. The forested areas tend to be interspersed
with bogs, lakes, and old stream channels supporting a variety of aquatic plant
communities.
Treeline and alpine vegetation
Treeline vegetation in the YMA is characterized by open stands of black and
white spruce that grade into alder and willow tall-shrub thickets and hummocky,
low-shrub birch (Betula glandulosa) communities. Alpine dwarf shrub plant com-
munities are typically found on the treeless ridge crests and domes at elevations
above 685 m (2250 ft) and consist of plants capable of withstanding very low tem-
peratures and short growing seasons. Much of this alpine zone is covered by a
crowberry (Empetrum hermaphroditum)/blueberry (Vaccinium uliginosum) dwarf
shrub tundra. These dominant species intermingle; however, shallow, stony, fairly
well-drained soils support blueberry tundra at slightly higher elevations than crow-
berry tundra. Blueberry tundra sites are generally exposed to the wind and do not
accumulate much snow in the winter but usually are not as exposed as sites sup-
porting Dryassedgelichen tundra (Viereck et al. 1992). Crowberry tundra occurs
in more protected areas at slightly lower elevations on thin, well-drained, mineral
soil or poorly drained peats.
A Cassiope dwarf shrub tundra (Cassiope tetragona) occurs on moist sites, com-
monly on north-facing slopes or snow accumulation areas. It is found on sites
well-protected by snow in winter that become snow-free in the early to middle part
of the growing season (Viereck et al. 1992).
On the other end of this moisture gradient, occupying exposed, wind-swept,
alpine sites, are species of the genus Dryas that form mats a few centimeters thick
and have a strong sedge and lichen component. Exposure to strong winds leads to
deflation of fines and organic material producing various-sized mats or islands of
this Dryassedgelichen dwarf shrub tundra along many of the higher ridges and
slopes in the YMA. Ridgelines of the highest alpine areas are also characterized by
tors. These rock outcrops are sparsely vegetated by alpine herbs, lichens, and mosses.
31
Previous Page
