Distinct bird assemblages emerge after fire versus forest harvest but converge with early seral forest development

Abstract

Anthropogenic changes to disturbance regimes, including intensified forest management, have been hypothesized to drive population declines in early seral forest birds. Species adapted to early seral conditions can benefit from timber harvest, but intensively managed stands often lack key habitat features that exist after natural disturbances. To evaluate how early seral bird communities differ between areas regenerating from natural (i.e., wildfire) and anthropogenic (i.e., timber harvest) disturbance, we sampled stands across a chronosequence of 2–20 years post-disturbance in southwest Oregon, USA, in sites regenerating after wildfire, clearcut harvest with intensive management, or post-fire salvage logging. We found that fire-origin stands supported 8.8 more species (90% CI: 4.1, 14.1; 54% more) than clearcut stands immediately following disturbance (2–5 years), including a greater number of cavity-nesting species. These differences diminished somewhat with stand age, but fire-origin stands still supported 4.9 more foliage-gleaning species (90% CI: 3.2, 6.5; 102% more) 6–9 years after disturbance. Differences in species richness and composition between disturbance types attenuated as stands approached canopy closure (16–20 years), suggesting that intensive management may emulate natural stand-replacing disturbance for birds that occupy developmentally advanced early seral forests. Salvage-logged stands exhibited few differences from unlogged fire-origin stands, although they supported 1.8 fewer (90% CI: 0.0, 3.4) cavity-nesting species 6–9 years after fire. Overall, distinct bird communities in recently burned forests suggest that these areas may be especially valuable for promoting biodiversity. Guilds more strongly associated with recently burned forests than harvested stands tended to be associated with biological legacies, including deciduous shrub cover, large residual trees, and snags. Therefore, emulating post-fire structural legacies and early seral vegetation in managed forests should enhance their value for birds, including species experiencing long-term declines.