Aspen-dominated forest response to drought in the Lake States
The Long Term Soil Productivity (LTSP) program was founded to examine the effects of soil disturbance, specifically impacts to soil organic matter and soil compaction, on fundamental forest productivity. Both have significant impacts on forest ecosystem function and are heavily influenced by management activities. The LTSP study design includes nine core combinations of organic matter removal and soil compaction. As treatment severity increases, potential net primary productivity is expected to decrease. This study takes place on the LTSP installation in the northern lower peninsula of Michigan, on the Huron National Forest where aspen-birch forest was clear-cut harvested and treated according to LTSP principles in early 1994. Current projections predict warmer temperatures, potentially longer growing seasons, and greater variability in precipitation that together have the potential to increase water stress for tree species, including aspen. The objectives of this study included answering the following questions related to forest response to stress, both anthropogenic and climate-related: 1) How do soil compaction, organic matter removal, and their potential interaction impact stand-level forest growth response to drought in 2012, and 2) how are individual trees responding to drought in 2012 given factors such as size, species, and crowding in addition to treatment effects? Our work showed that there were no stand-scale growth responses to the 2012 drought associated with treatments, but species responses varied. At the individual tree scale, factors such as diameter, species, and crowding were better indicators of drought resistance, resilience, and recovery to drought than treatments. This research has particular value within a landscape that has a long history of management and will likely continue to provide conventional timber products, even as global environmental change introduces new stressors for forests. Additionally, as demand for more sustainable energy sources increases, bioenergy feedstocks may be increasingly sourced from these forests. As a result, aspen stands in the Lake States may be expected to meet greater demand. This could mean more frequent harvest, an increased likelihood of soil compaction, and an increase in the biomass removed if residues are utilized for bioenergy feedstocks or other comparable products, thus understanding the long-term effects of such disturbances on stand growth and response to climate conditions is increasingly important.