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 will likely continue to provide conventional timber products, even as global environmental as Abstract 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. This project takes place on the LTSP installation in the northern lower peninsula of Michigan, on the Huron National Forest which has a primary composition of aspen-birch forest type that was clear-cut harvested and treated according to LTSP principles in early 1994. This project examines the stand-scale and individual tree scale response of this forest to a region-wide drought that occurred in 2012. The ecological indices of resistance, resilience, and recovery and tree cores collected from the site in 2018 were used to evaluate drought responses. 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, model selection showed that size, species, the interaction between size and species, and the interaction between crowding and species were better indicators of drought resistance and recovery to drought than treatments and their interaction, and drought resilience was best modeled by size, species, crowding, the interaction between size and species, and the interaction between crowding and species.