Disturbance type shapes initial community assembly patterns of early seral forest ground beetles in southwest Oregon

Forest harvests are a significant part of disturbance regimes in many temperate forest landscapes. However, variability in biodiversity between early seral stands originating from harvest versus natural disturbances like wildfire is not well understood. We used a chronosequence sampling design to compare diversity, composition, and traits of ground and tiger beetles (Coleoptera: Geadephaga, hereafter “ground beetles”) between early seral stands regenerating within 20 years after clearcut harvest or stand-replacing wildfire in southwest Oregon, USA. Clearcut stands were managed with planting and herbicides whereas fire-origin stands received minimal post-fire management. We also compared ground beetle communities 6–9 years after post-fire salvage logging. Compared to young clearcut stands (2–5 yr), ground beetle communities in young fire-origin stands had 30 % higher species richness (90 % CI: 0, 60 %), distinct composition, and disturbance-adaptive traits, including small body size (90 % CI for trait-environment interaction: −1.72, −0.63) and flight ability (90 % CI: 0.39, 1.47). Communities converged in the oldest age class (16–20 yr). Salvage logging favored flight-capable species to a greater degree than unlogged fire-origin stands (90 % CI: 0.12, 1.02) up to 9 years after disturbance, suggesting prolonged early seral conditions. Ground beetle composition varied with vegetation and deadwood structure but was also likely influenced by unobserved processes, such as fire-induced beetle mortality exceeding that of timber harvest. Our results indicate an ephemeral ground beetle community inhabiting post-fire stands that differs from post-harvest environments, suggesting that fire effects on the forest floor have a distinctive role in shaping early seral forest biodiversity. • Comparisons to natural disturbance provide useful context for understanding conservation implications of forest harvests • We compared ground beetle biodiversity after timber harvest, wildfire, and post-fire salvage logging • Ground beetles were more diverse and had more disturbance-adapted traits in the short-term after fire than harvest • Ground beetle communities converged by 16–20 years after disturbance