Effects of spruce beetle (Dendroctonus rufipennis) outbreaks on fuels, carbon, and stand structure and composition in Utah and western Wyoming (Project INT-EM-F-13-02).
The objectives of this study (INT-EM-F-13-02) were to document changes in residual stand structure and composition associated with ground, surface, and aerial fuel loads; tree age, size, and species diversity; regeneration; invasive plants; and snag demography. To achieve this, monitoring plots were established in forest stands in Utah and Wyoming, USA, spanning a temporal continuum of tree mortality attributed to spruce beetle (i.e., prior to epidemic (pre), during epidemic or incipient epidemic (epidemic), and post-epidemic (post)). Results showed that in 2013, significant differences were measured in fine surface fuels for 100-hour fuels among outbreak phases, but not for 1- or 10-hour fuels. Following remeasurement in 2015 significant differences in 10- and 100-hour fuels were observed, which indicates the current epidemic may be winding down since no differences were measured in 1-hour fuels as seen in other systems (e.g., mountain pine beetle (Dendroctonus ponderosae) in lodgepole pine (Pinus contorta)). In summary, changes in fuel loading and stand structure were consistent with other studies, where fine fuels increase during epidemics, standing live trees decrease, and standing dead trees increase. Changes in regeneration were consistent with a previous findings with subalpine fir regeneration dominating and Engelmann spruce regeneration low.