Response of the surface-active beetle community (Coleoptera) to mixed-conifer forest restoration thinning and burning treatments in northern New Mexico, USA.

Forests in the western United States are experiencing increasing stresses from more frequent stand-replacing fires, insect outbreaks, and droughts. To mitigate these phenomena, forest managers are increasingly employing forest fuels management operations (tree thinning and prescribed fires) to reduce fire severities and inter-tree competition for water and soil nutrients. While such forest restoration programs have proven effective, the impacts on forest arthropod communities are largely unreported. In this 6-year case study, we examined the response of a surface-active (epigeic) beetle community (Coleoptera) in a mixed-conifer forest subjected to tree thinning followed by a prescribed broadcast slash burn. We used a Before-After/Control-Impact (BACI) design to test treatment effects on the beetle community composition, diversity, richness, evenness, individual species abundances, and trophic structure. We documented 289 taxa of Coleoptera and found that treatments caused significant changes in the beetle community's composition, with 21 common species increasing and 35 species declining in the more open post-treatment sub-canopy environment; only 3 common species were extirpated from the treatment sites, while 2 common species colonized the post-thinned/burned areas. Saproxylic species exhibited a decrease compared to controls after thinning and prescribed fire. Trophic structure species composition did not change, although numbers of individuals increased in the omnivore, fungivore, and detritivore trophic groups. Overall, our forest restoration treatments did not reach the level of impact from more severe forest disturbances (clear-cutting, or high-severity wildfires) and created a mosaic of grassy forest understory and small open meadow patches that would contribute to increased landscape arthropod diversity.