Terrestrial carbon and nitrogen following massive scale beetle-caused forest mortality

Bark beetle epidemics have decimated at least 12 million hectares of lodgepole pine and Engelmann spruce forests in western North America. As a result, belowground biogeochemical processes are changing from sequestration and retention of carbon (C) and nitrogen (N) in form of tree vegetation biomass, soil and surface litter towards loss through multiple interrelated pathways and re-allocation to the recovering understory vegetation. The main objective was to assess terrestrial C and N in soil and forest vegetation understory four years after the infestation. The research was conducted at the "No Name" watershed in the Snowy Range Mountains in southeastern Wyoming between June and October 2015. The site was selected because of the evidence of partial infestation by beetle that left some of the trees alive. Plots were established in three slope locations (toeslope, footslope and shoulder) and within, in clusters of dead and live trees, all replicated five times. Data included total soil C and N in soil (0-10 cm), surface litter, plant roots and understory vegetation. All values added were termed "terrestrial C and N". In addition, soil pits, overstory tree size and density were described. Initial results showed the greatest differences in terrestrial C and N between dead tree clusters and live tree clusters in the shoulder position of the slope only (32% and 37%, respectively). This was driven mainly by greater accumulation of N rich litter suggesting that the post-beetle forest recovery may take longer at locations that are drier and dominated by lodgepole pine forests.