Long-Term Soil Changes from Forest Harvesting and Residue Management in the Northern Rocky Mountains

Soil changes associated with forest harvesting, differing utilization levels, and post-harvest prescribed burning were determined using an empirical study to investigate the long-term impacts on soil physical and chemical properties at Coram Experimental Forest in northwestern Montana. In 1974, two replications of three regeneration cuttings (shelterwood, group selection, and clearcut) were installed. In addition, four residue management regimes (high utilization with no burning, medium with no burning, medium with broadcast burning, and low with broadcast burning) were implemented (similar to 74, 63, 65, and 54% wood removal, respectively). Thirty-eight years after harvesting, changes were evaluated in mineral soil and forest floor physical and chemical properties (organic matter [OM], C, N, Ca, K, and Mg pools, soil bulk density, and pH) and in coarse woody debris levels. There were no differences in soil pH and bulk density across all regeneration cuttings and residue treatments, probably due to the minimal soil effects associated with the forest harvesting operations that were used (hand felling and cable yarding). Comparisons between harvest and burning and the control indicate no statistical differences in OM, C, and N contents. Minor differences in extractable cation pools were noted in several comparisons among the treatments; these may be attributed to litter inputs from the differing vegetation compositions of over-story and shrub layers rather than nutrient changes within the mineral soil itself. At this moist-cool forest, intensive biomass utilization, with or without broadcast burning, had few long-term impacts on soil properties of soil C, OM, and nutrients.