Landcover Class Information
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The peatland landcover class occurs on peatlands (bogs and fens) south of the Alaska Range. The peatlands north of the Alaska Range are not included in this class. The peatland landcover class is comprised of a variety of already defined landcover classes that occur on peat deposits including stunted spruce, willow, dry-mesic herbaceous and wet herbaceous. In addition, the Myrica gale plant association occurs in this landcover class. This combination class is defined because it is spectrally distinct on the south side of the Alaska Range, and the individual classes could not be spectrally separated reliably on peat deposits. The class is comparable to the Viereck et al. (1992) hierarchical levels open needleleaf forest (IA2), needleleaf woodland (IA3), open dwarf tree scrub (IIA2), dwarf tree scrub woodland (IIA3), closed tall willow (IIB1a), open tall willow (IIB2a), closed low willow (IIC1b), open low scrub (11C2), dry graminoid herbaceous (IIIA1), mesic graminoid herbaceous (IIIA2), dry forb herbaceous (IIIB1), mesic forb herbaceous (IIIB2), wet graminoid herbaceous (IIIA3) and wet forb herbaceous (IIIB3).
The peatland landcover class is found only in the lowlands (74 to 315 meters based on field data; Table 3) south of the Alaska Range. Peat deposits (i.e., peatlands, muskeg, bogs, fens) are composed of >0.5 meters of accumulated peat in areas of restricted drainage with water tables at or close to the peat surface. They occupy former lake basins and other closed depressions, alluvium along some valley floors, and are abundant on older glacial drift deposits within the boreal forest. The class covers 0.04% (2,304 acres) of Denali National Park and Preserve (Table 5). Peatlands are generally found adjacent to forested areas in Denali. The gradient of nutrient availability and water sources in peatlands is typically divided into nutrient rich (fen) and nutrient poor (bog) peatlands. Fens arewetlands with wet organic soils, dominated by aquatic, emergent, and dwarf shrubs, or raised peat dominated by shrubs and trees. Ground water, the primary water source in a fen, is nutrient rich because of its contact with mineral soils. Waters may be acidic or basic, but typically with a pH above 4.7. Water is lost through evapotranspiration, seepage (infiltration through the soil), and surface outflow.Fens arewetlands with organic soils, typically dominated by Sphagnum (peat moss) species, sedges, grasses, or reeds. Bogs require depressions (ponds) in level areas where precipitation exceeds evapotranspiration. Precipitation is the primary water source in a bog, with little or no ground-water flow. Consequently the sites are nutrient-poor and acidic, commonly with a pH less than 4.7. The water table is at or close to the surface most of the year. Because of the continuum of site and vegetation change within a peatland, it is often difficult to clearly separate a fen from a bog in the field.
In level areas, peatlands generally exhibit recognizable and consistent vegetation zonation patterns that are directly associated with different water depths. The vegetation, on a wet to dry moisture gradient, changes from aquatic (pond), to emergent and mesic herbaceous (Calamagrostis canadensis, Carex rostrata, C. aquatilis and Eleocharis quinqueflora), to shrub-dominated wetland (Myrica gale and Betula nana), to dwarf tree (Picea mariana). Sphagnum species occur in most dominance types. Not all the vegetation zones are always expressed, and the zonation may change abruptly, such as from a pond to a shrubland. Fens on ground with a slight gradient and with heavy subsurface and surface waterflow often develop a patterned ground of vegetated ridges, and vegetated or unvegetated hollows filled with water.
The producer’s accuracy for the peatland class is 82.3%, with a user’s accuracy of 80.9%. Most of the errors of commission and omission are with the low shrub-sedge class.Plant associations occurring within the Dwarf Shrub landcover class:
- Arctostaphylos alpina plant association (Alpine blueberry)
- Cassiope tetragona plant association (Four-angled cassiope)
- Dryas octopetala, Cassiope tetragona, Vaccinium uliginosum, Salix reticulata, Salix arctica, feathermoss, Stereocaulon species
- Dryas octopetala, Salix arctica, Carex microchaeta, Oxytropis nigrescens, Hylocomium splendens
- Dryas octopetala, Vaccinium uliginosum, Salix arctica, Carex microchaeta, Hierochloe alpina, Hylocomium splendens
- Salix brachycarpa, Dryas octopetala, Salix reticulata, Cassiope tetragona, feathermoss
- Salix glauca, Salix reticulata, Festuca altaica, Dryas octopetala
- Salix polaris plant association (Polar willow plant)
- Salix reticulata, Carex membranacea, Eriophorum angustifolium, Dryas integrifolia, Sphagnum species
- Vaccinium uliginosum/Dwarf shrub plant association (Bog blueberry/Dwarf shrub)