Effects of Soil Compaction and Organic Matter Removal on Ground-flora Diversity: Seventeen-year Results from the Chippewa National Forest Long-term Soil Productivity Project

Abstract

Soil is one of the key factors regulating the productivity and diversity of forest ecosystems. Soil organic matter resulting from the decomposition of leaf litter and branch and bole material provides an important reservoir of nutrients for future forest growth. The structure of soils, in conjunction with soil texture, determines the ability of a soil to retain moisture. Forest harvest operations, through the use of heavy equipment and slash management practices, have the potential to damage soil structure and remove organic matter from the forest floor. We lack a clear understanding, however, of which soil types are most susceptible, and what degree of impact soils can sustain before the potential productivity and diversity are reduced. To address this issue, the US Forest Service initiated a nationwide Long-Term Soil Productivity (LTSP) study to assess the effects of logging operations on the structure and organic matter content of forest soils (Powers et al. 1990). In the Lake States, study plots were installed on the Chippewa, Ottawa, and Huron National Forests. These plots represent the range of soil textures which occur across the Lake States: silt loams, clays, and sands, respectively. Using an experimental approach, different levels of soil compaction and organic matter removal were applied to harvested aspen stands across this soil gradient. Aspen reproduction, forest biomass, and the diversity of the ground-flora layers are being monitored on a periodic basis to assess their response to these treatments. The results of this experiment will allow us to predict the degree of protection required to sustain productivity and floristic diversity in aspen stands across a range of common Lake State soil types.The Lake States LTSP study included an analysis of floristic diversity to the suite of measurements made on the study plots. Biodiversity and forest management have become critical issues in the Lake States Forests. In Minnesota’s Generic Environmental Impact Statement, diversity was one of the key focal issues. Ground-flora has received wide use as ecological indicators and in ecological land classification systems across the Great Lakes (Spies and Barnes 1985, Host and Pregitzer 1991, Coffmann et al. 1983, Shadis et al. 1995, MN DNR 2003). A study by Berger, Peuttmann and Host showed a strong response of ground-flora to on-site operations, particularly on landings and skid trails, which receive a high degree of compaction (Berger, Peuttmann and Host 2004). The rate and degree to which sites recover from compaction, however, is poorly understood. The primary objective of this study was assess changes in species richness, diversity and community composition seventeen years after installation of the LTSP treatments on the Chippewa National Forest of north central Minnesota.