Are we maintaining aspen productivity on sand soils

—Management activities that decrease soil porosity and/or remove organic matter have been associated with declines in site productivity. We determined effects of soil compaction and organic matter removal (OMR) on soil properties and aboveground productivity of aspen (Populus tremuloides Michx. and P. grandidentata Michx.) suckers, associated woody species, and herbaceous vegetation on a Rubicon sand in northeastern lower Michigan. Three levels of OMR—(1) merchantable bole harvest (MBH), (2) total tree harvest (TTH), and (3) TTH plus forest floor removal (FFR)—and three levels of soil compaction were applied. Compaction and FFR each increased fourth-year sucker density about 20%. “Heavy” compaction increased aspen diameter and height by about 10% and biomass by 20%. FFR decreased sucker diameter, height, and dry weight by more than 20%. Total aboveground biomass production (herbs + shrubs + aspen + associated species) decreased with increased OMR. Retention of organic matter appears critical to sustaining long-term productivity of aspen-dominated ecosystems on sand soils. As an interim guideline for aspen harvesting on sand soils, we recommend limbing at the stump and retaining of slash on site. USDA Forest Service, North Central Research Station, 1831 Highway 169 East, Grand Rapids, MN 55744; e-mail: dstone/nc_gr@fs.fed.us Huron-Manistee National Forest, 5761 North Skeel Avenue, Oscoda, MI 48750; e-mail: jgates/r9_huronmanistee@fs.fed.us Maintaining site productivity is a key factor in sustainable forest management. Forest management activities that decrease soil porosity and remove organic matter have been associated with declines in site productivity (Agren 1986, Greacen and Sands 1980, Grier et al. 1989, Standish et al. 1988). As part of an international network of cooperative studies on long-term soil productivity (LTSP) (Powers et al. 1990, Tiarks et al. 1993), we are monitoring effects of soil compaction and organic matter removal (OMR) in the aspen (Populus tremuloides Michx. and P. grandidentata Michx.) forest type across a gradient of soil productivity on four sites across the northern Lake States region and in southeastern British Columbia (Kabzems 1996, Stone and Elioff 1998). The research is designed to determine how changes in soil porosity and organic matter content affect fundamental soil processes controlling forest productivity and sustainability; and secondly, to compare responses among major forest types and soil groups across the United States and Canada. The objective of this installation is to monitor changes in soil properties following forest harvesting and application of soil compaction and OMR treatments on a sand soil, and to measure responses by the forest regeneration and herbaceous vegetation. We use the term “sand” as in the commonly used USDA textural classification scheme i.e., 85% or more sand-size particles (Soil Survey Staff 1975). We report results on aspen stocking and growth and aboveground biomass production of aspen and associated vegetation after four growing seasons and compare them with data from a loamy sand site in northern Minnesota.