Classification of forested histosols in southeast Alaska

Organic soils are an important substrate for cycling carbon between terrestrial and atmospheric pools. The degree of decomposition of organic soil material influences the physical and chemical characteristics that control the carbon cycles in these soils. Although organic soils are abundant in southeast Alaska, little information is available on the state of decomposition or variability within organic soil mapping units. Determination of physical (fiber content) and chemical (sodium pyrophosphate extract color, SPEC) decomposition is used to classify organic soils and subsequently establish map units. The purpose of this study is to provide physical and chemical decomposition data to better characterize and classify, forested organic soils in southeast Alaska and to improve our understanding of the distribution of fiber within these soils. Fiber content and pyrophosphate color were determined on 115 samples from 23 organic soils from throughout the Tongass National Forest. These samples show that complexes of hemic and sapric suborders mapped in the Tongass Soil Survey are dominantly hemic. Some Fiber analyses differ considerably from statements in descriptions of established series in the Tongass Soil Survey. Physical decomposition of the fibers is in the hemic range, but chemical decomposition indicated by SPEC is sapric due to accumulation of soluble organic matter by water movement down steep slopes as well as in situ decomposition. Suborder classes provide a means to incorporate appropriate decomposition levels into existing soil series.