Vegetation on the Coastal Plain
Several tundra vegetation and landform types occur within the region, including thaw lake plains, hilly coastal plains, foothills, and flood plains.
On the tundra, microclimates which are responsible for much of the species diversity in the region are dynamic. The growth of ice wedges causes soils to be pushed upward exposing the vegetation to prevailing winds; the same process deepens the troughts between polygons. Over time, plant species at a particular site will change along with subtle changes in the microclimates.
Thaw lake plains. characterized by polygonally patterned ground and shallow pond complexes, occur in less than 3 percent of the ANWR study area. The thaw lake plain extends up to 10 miles inland from the Beaufort Sea coast. This terrain type is similar to that of the main portion of the Prudhoe Bay oil field, consisting of numerous thaw lakes, drained lake basins, and expanses of low-centered ice-wedged polygons. Microtopography in this terrain type has a major influence on the distribution of plant communities.
Vegetation in drained lake basins consists of aquatic and wet tundra species including pendant grass, aquatic sedges, and cottongrass. Species commonly found in wet tundra areas are sedges, cottongrasses, a few herbaceous plants and mosses. These plant communities are considered to be particularly important for nesting birds and are heavily grazed by waterfowl prior to the fall migration. In saline soils, primary species are alkali and scurvy grasses, sedges and chickweed.
Hilly coastal plain terrain contains gently rolling topography and poorly developed ice-wedge polygons. This terrain type is found in 22 percent of the study area. Well-drained sites within the Coastal Plain or the rolling hills farther inand harbor vegetation which includes sedges, mosses, crustose lichens, and prostrate shrubs. Species commonly found in these areas are several varieties of willows and herbaceous plants. On small hummocks, communities of avens and sedges occupy sites with mosses and crustose lichens.
Tussock tundra occurs frequently in the relatively well-drained soils of the hilly plain. Vegetation in these areas consists of a high percentage of cover of cottongrass with dwarf birch, and Laborador tea. Tussock tundra is dynamic; in these vegetation communities, older tussocks age and die. Other plant species then revegetate the site. Scientists have observed that revegaettion of areas where tussocks have been dfamaged by vehicular traffic is similar to revegetation due to natural succession within plant communities.
Foothills comprise about 45 percent of the study area and are characterized by hills separated by drainage channels, giving the slopes a decidedly ribbed appearance. Vegetation in the foothills is primarily sedge tussocks and dwarf shrub willow, birch, and alders. The height and density of these plants varies with the amount of protection provided to the shrubs by surrounding slopes. In deep drainages where the plants are protected from scouring winds, willows may reach heights of six feet, compared to the dwarf shrubs of the coastal plain that seldom exceed several inches in height.
River flood plains, which make up about 25 percent of the studty area, are typified by barren deltas and braided river channels and the terraces and alluvial deposits associated with old river channels.
The remaining area consists of alpine tundra, occurring at the southern boundary of the study area.