Post-spruce beetle timber salvage drives short-term surface fuel increases and understory vegetation shifts.
Recent, widespread spruce beetle (Dendroctonus rufipennis) outbreaks have driven extensive tree mortality across western North America. Post-disturbance forest management often includes salvage logging to capture economic value of dead timber, reduce fire hazard, and meet other social or ecological objectives. Little is known about effects of salvage logging on surface fuel loads or plant understory communities in Engelmann spruce (Picea engelmannii)-dominated forests. We sampled fine and coarse woody debris, ground cover, and plant species composition along transects in spruce-beetle impacted stands in southwestern Colorado, USA. Twenty stands had been subject to clearcut 1-2 years prior to sampling; 32 stands were unlogged controls. Salvage logged stands exhibited altered surface fuels, ground cover, plant species cover, and community composition. Salvage increased 1-, 10-, and 100-hr fuels, and cover by bare ground and woody debris; cover by litter and cryptogams was reduced. Understory plant cover was reduced in salvaged stands, primarily due to losses of shrub cover. We found no difference in species diversity or richness between treated stands and controls. Salvage logging also drove shifts in plant community composition. Mean cover by non-native species was low, and not different, between control and salvage stands. Our study characterizes short-term effects that will undoubtedly change substantially over longer periods, in particular due to anticipated tree seedling growth and movement of standing dead wood from the canopy to the surface. In the near term, abundant fine woody surface fuels at salvage sites could influence the likelihood and rate of spread of surface fires, though over time we expect surface fuels in untreated stands to increase to comparable or greater levels than in salvaged stands. Differences in vascular plant cover and composition imparted by salvage harvests is also expected to change over time, though whether treated and untreated communities diverge or converge is not known. As such, we recommend that salvage harvest effects be monitored over extended time frames in order to detect longer-term trends.