Shrubscrub vegetation
Nonforested sites at lower elevations are occupied by a wide variety of plant
communities, many of which may be successional to forested site types. Alder (Alnus
tenuifolia, Alnus viridis) and willow (Salix bebbiana, Salix spp.) shrub communities
are very important successional species on exposed river bars, old alluvial deposits
of creeks and rivers (Mann et al. 1995, Viereck 1989), and disturbed sites such as old
trails and clearings. They also occur in openings of spruce and birch forests and
become the dominant vegetation where they intermingle with spruce forests and
dwarf birch low-shrub types at treeline.
Peatlands
Much of the Chena River lowlands and Tanana Flats are characterized by treed
and treeless bog and fen wetland types. Some are dominated by Sphagnum mosses,
some by Eriophorum vaginatum tussocks, and some by mixtures of sedges (Carex
spp.) and grasses. They may be completely treeless or have widely scattered black
spruce, paper birch, and occasional tamarack. Much of the vegetation of the Tanana
Flats is a complex mosaic of such stunted forests and expanses of dwarf birch low-
shrub communities heavily influenced by beaver activity and wildfire (Racine and
Walters 1994).
Calmes (1976) described three major bog types from the Fairbanks area. The first
type is a Sphagnum bog dominated by a moss layer of Sphagnum and with an im-
portant shrub component of dwarf birch, bog rosemary (Andromeda polifolia), and
narrow-leaf Labrador tea (Ledum palustre ssp. decumbens). Sphagnum bog types gen-
erally develop a substrate of sedge and Sphagnum peat that may form a floating
mat on water along the shoreline of lakes and ponds.
A second bog type, found on wetter sites, is dominated by several species of
sedges (Carex spp.) and grasses and is nearly devoid of shrubs. Sphagnum mosses
are present but are much less important than in the Sphagnum bog. There is a gradual
transition from Sphagnum bogs to sedge meadows on progressively wetter sites.
A third and widespread type of bog is dominated by tussocks of Eriophorum
vaginatum similar to those found in many parts of more northerly arctic and alpine
tundra areas. Low shrubs of Ledum palustre ssp. decumbens, Vaccinium uliginosum,
Vaccinium vitis-idaea, Betula nana, Betula glandulosa, and Salix spp. are common in
the tussock type. Vast portions of the Tanana Flats are covered by such dwarf birch
tussock sedge bogs.
A unique area in the northwest corner of the Tanana Flats is covered by ground-
water discharge "fens" recently described by Racine and Walters (1994). These ar-
eas contain highly productive, floating vegetation mats made up of narrow-leaved
graminoids and broad-leaved forbs that possess little or no Sphagnum moss or woody
plant species. Fens occur as both large open expanses and long linear corridors
100500 m (3001500 ft) wide and oriented southeast to northwest in the north-
western portion of the study area (Fig. 13) and are used extensively by airboats.
Xeric steppe
In sharp contrast with the waterlogged conditions of these treed and treeless
bog and fen types are xeric sites on steep, south-facing bluffs (Fig. 22). These are
found on the Wood River Buttes (Fig. 12), Clear Creek Butte, and Blair Lake hills on
the Tanana Flats, and bluffs adjacent to the Chena River floodplain along the base
of Birch and Sage Hill. Steppe-like communities exist on some of these sites that are
too dry for tree growth and are dominated by sagebrush (Artemisia frigida), juniper
(Juniperus communis), and grasses and forbs that include Calamagrostis purpurascens,
rosea.
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