While conducting USDA-NRCS initial soil survey in the Yukon River Basin of Alaska, surveyors characterized grassland plant communities and associated soil types unique to Interior Alaska and the subarctic region. These terrace landforms contain sodic alluvial and lacustrine materials deposited in abandoned river channels and shallow lake basins, and are not underlain by permafrost within 2m depth. The soils contain calcite, dolomite, gypsum, halite, and trona and generally classify as Sodic Hydraquents or Typic Halaquepts.

The combination of sodic parent material, high pH, basin hydrology, and high potential evapotranspiration rates favors plant communities that differ significantly from the common lowland boreal forest, tussock tundra, and shrub-scrub plant communities typically found in this region. Plant community phases associated with this ecological site can be grass dominant when soils are dry or sedge dominant when soils are wet. It is also common to find sparsely vegetated, salt encusted playettes adjacent to these plant communities in the lowest microtopographical positions.

Hydrological conditions are variable between grassland depressions and are thought to be primarily controlled by annual active layer thaw, snowmelt runoff, and precipitation. Low average annual precipitation (170mm per year) make these depressions especially prone to drying during drought years. However, they are frequently ponded during wetter climatic cycles. We speculate that these terrace depressions may actually be open taliks (basins surrounded on all sides by permafrost) and may have water tables independent of each other.

As part of an initial soil and vegetation inventory, this research provides a basis on which to conduct more detailed studies of wildlife management, subsistence hunting and gathering, and climate change in the Yukon River basin. From a pedological perspective, this work offers insight into soil-plant-hydrology relationships in a complex subarctic alluvial basin and invites comparisons with similar landforms and plant communities at high latitudes.