Michael C. Amacher
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Forest Inventory and Analysis (FIA) Characterization of Aspen and Conifer Soils in the Interior West
Michael C. Amacher and Dale Bartos,USDA Forest Service, Logan, UT
Soils are the product of five soil forming factors: parent material, climate, landscape position, organisms, and time. Vegetation can and does have a major influence on the physical and chemical properties of forest soil. Mineral soils under conifers tend to have a leached layer, be more acidic, and are lower in organic matter and nutrient content. Aspen leaves are rich in nutrients, and aspen stands, when healthy, have a large understory of grasses and forbs. Thus, aspen soils tend to be relatively high in organic matter and nutrients and are usually only moderately acidic. As conifers invade aspen stands, there is a potential for soil property changes over time that would inhibit aspen re-establishment. Limited sampling of soils under mixed aspen-conifer stands on the Fishlake National Forest showed that many aspen-conifer forest soils could still support aspen regeneration if appropriate treatments were applied. A more extensive sampling of forest types throughout the Interior West as part of the FIA Soil Indicator of Forest Health showed that aspen soils tend to have lower bulk densities, attributable to aspen sinker and lateral rooting habit, understory vegetation, and burrowing fauna. Aspen soils also tend to be higher in soil organic matter and nutrients. Decline and loss of aspen from the Interior West landscape could have long-term consequences for forest soil productivity and hence, forest productivity.