Globally, there is widespread interest in using forest-derived biomass as a source of bioenergy. While conventional timber harvesting generally removes only merchantable tree boles, harvesting biomass feedstock can remove all forms of biomass (i.e., trees down through to forest floor material) resulting in a greater loss of biomass, nutrients, and habitat from a site. To investigate the potential impacts of this practice, this study examined the initial impacts (pre- and post-harvest) of various levels of slash and live-tree retention on biomass and nutrient stocks in Populus tremuloides-dominated forests of northern Minnesota. Treatments examined included 0%, 20%, and 100% slash retention with no, dispersed, and aggregate live-tree retention.
Slash retention was the primary factor affecting immediate post-harvest biomass and nutrient stocks within total ecosystem and woody debris pools. High levels of biomass and nutrients in harvest slash were observed in all treatments compared to the unharvested control. Typically, 100% slash retained treatments contained significantly greater biomass and nutrient stocks than no slash retained treatments. Stocks of biomass and nutrients within the 20% slash retained treatment, a slash retention level currently recommended by Minnesota’s biomass harvesting guidelines, were generally similar to both no slash retained and 100% slash retained treatments.
Given the importance of fine woody debris as a source of nutrients following harvest, nutrient concentrations were measured across an array of woody debris size and decay classes within the Populus tremuloides-dominated forests examined. Results indicate that fine woody debris has significantly greater nutrient concentrations than coarse woody debris. In addition, nutrient concentrations generally increased within both coarse and fine woody debris as decay progressed. Collectively, the results of this study underscore the importance of deliberate retention of fine woody debris as a source of nutrients following harvests of biomass feedstocks.
University of Minnesota M.S. thesis. February 2012. Major: Natural resources science & Management. Advisors:Anthony W. D’Amato, John B. Bradford. 1 computer file (PDF); viii, 90 pages, appendix A.
Klockow, Paul Alan.
Impacts of biomass harvesting on biomass, carbon, and nutrient stocks in populus tremuloides forests of Northern Minnesota, U.S.A..
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