Arthropod responses to harvesting and wildfire: Implications for emulation of natural disturbance in forest management

Although natural disturbance has been widely adopted as a template for forest management that protects biodiversity, this hypothesis has not been adequately tested. We compared litter-dwelling arthropod assemblages (Coleoptera: Carabidae and Staphylinidae; Araneae) in aspen-dominated stands originating as clear-cuts or wildfires across three age classes (1–2, 14–15, and 28–29 years old) to test whether the post-harvest and post-fire assemblages converged following disturbances, and to compare faunal succession. These findings were compared to data about epigaeic arthropods in old and mature pyrogenic aspen stands (>70 years old) to determine whether diversity and community composition of arthropods from the younger age-classes approached what may have been typical pre-disturbance conditions. The resulting data-set of almost 27,000 arthropods and 230 species showed convergence in most taxa, and some general similarities between 28- and 29-year-old stands and old and mature stands. However, not all taxa responded similarly, and faunal succession following clear-cutting appeared to progress more rapidly than following wildfire. Rarefaction-estimated diversity was elevated in 1–2-year-old stands, compared to unharvested stands, reflecting a mix of closed-canopy and open-habitat species. Non-metric multi-dimensional scaling ordinations showed that samples from young wildfire disturbed stands (1–2 years old) included more variable assemblages than all other study sites, and contained species that may depend on unique post-fire habitat characteristics. The fauna of old and mature stands exhibited low diversity, but contained species with limited dispersal abilities, and species tied to old-growth habitats such as dead wood. Harvesting systems that do not allow adequate recovery following a first harvesting pass, or do not maintain microhabitat features associated with older fire-origin forests, may threaten persistence of some elements of boreal arthropod faunas.