State Factor Control of Soil Formation in Interior Alaska

The most striking feature of Alaska’s boreal soils, compared to those from most other biomes, is the lack of significant soil development even though much of interior Alaska has not been glaciated for millions of years. Soils in the boreal region support forest ecosystems that account for nearly half of the land area of Alaska. Worldwide, boreal forests store nearly a third of the terrestrial carbon (Apps et al. 1993). Hence, changes in boreal soils could greatly impact the global carbon balance (Chapter 19). Another striking feature of boreal soils is their great local variation due to slope and aspect. Compared to the well-developed, colorful soils of the temperate and tropical regions, boreal soils generally have ochric (yellowish brown) colors in uplands and dark-colors in lowlands due to organic matter accumulations. These lowlands account for 85% of the wetland inventory in the United States (Bridgham et al. 2001). Soil is a mixture of geological parent material and organic matter altered by weathering and the action of living organisms and conditioned by topography over time. Jenny (1941) defined the major factors that influence soil formation as parent material, organisms, topography, climate, and time. When only one of these factors varies, soil characteristics can be treated as a function of that factor (Chapter 1). Soils are also responsive to anthropogenic changes, such as agriculture and forestry, that alter interactive controls at the local scale (Moore and Ping 1989). Interior Alaska consists of several broad, nearly level lowlands with elevations mostly below 500 m and rounded mountains with elevations up to about 2000 m (Wahrhaftig 1965). The Interior Highlands Ecoregion (Chapter 2) includes the Kuskokwim Highlands and the Interior Highlands. The Interior Bottomlands Ecoregion includes the Koyukuk-Innoko Lowland, the Kanuti Flats, and the Tanana- Kuskokwim Lowlands (Rieger et al. 1979). The Copper River Basin south of the Alaska Range has a climate and vegetation similar to that of interior Alaska. The Copper River Basin has fine-textured subsoils of lacustrine origin. Soils from the Alaska Range, the Kuskokwim, and the Interior Highlands generally form in glacial deposits and residual materials and have abundant rock fragments.