Implications of Salvage Logging on Soil Organic Matter Physico-Chemical Protection and Ecosystem Carbon Stocks in Bark Beetle Infested Lodgepole Pine Forests.

Mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) outbreaks have affected over 7 million hectares of lodgepole pine (Pinus contorta) dominant forests in western North America with high overstory mortality. The outbreak occurred from the early-2000’s to a peak in 2006-2009 and in response to the mortality salvage logging increased. In general, contributions of coarse woody debris to soil organic matter are not well understood in the low productivity, dry-coniferous forests that were impacted by recent MPB outbreaks. Therefore the consequences of salvage logging and logging residue (i.e., biomass) management practices on soil organic matter (SOM) protection and soil carbon (C) and nitrogen (N) stocks, as well as short- and long-term productivity are not known. At 12 sites in Northern Colorado we compared untreated bark beetle-infested forest and similar, adjacent salvage logged stands that received either woody residue retention or removal. We are using a density and physical fractionation approach to quantify the size of the light, particulate and mineral-associated soil organic matter fractions and quantifying total soil C and N in each management treatment. Ion exchange resins are being used to measure exchangeable inorganic-N. Six years after harvesting there are significant differences in tree species composition and seedling growth between management treatments. We anticipate that soil responses will track patterns of aboveground productivity and help elucidate the linkages between woody biomass retention or woody biomass removal on ecosystem productivity and SOM stocks in MPB-killed forests.