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.

Keywords: Klamath Mountains; Oregon; avian point counts; bird community composition; clearcut; early successional forest; intensive forest management; occupancy modeling; post‐fire salvage logging; species richness; wildfire.

FIGURE 1

Map of study area and sampling locations (a) reproduced from Frank et al. (2025) under a Creative Commons license https://creativecommons.org/licenses/by‐nc‐nd/4.0/, and example photos of each disturbance type, including (b) fire‐origin stand (stand age: 8 years), (c) post‐fire salvage‐logged stand (stand age: 8 years), and (d) clearcut stand with intensive forest management (stand age: 7 years). Photographs in panels (b–d) were taken by Graham S. Frank.

FIGURE 2

Stand‐level species richness estimates for (a) all bird species, (b) specific foraging guilds, and (c) specific nesting guilds across disturbance‐age categories of early seral forest in southwest Oregon. Estimates are expected values in a given disturbance‐age category based on the sum of all species occupancy probabilities, after accounting for imperfect detection. Points and vertical lines represent the median and 90% Bayesian credible interval of the posterior distribution for this estimate. Note the different y‐axis scales for each panel.

FIGURE 3

Average predictive comparisons (APCs) for (a) total or (b) guild‐specific species richness across early seral structural and vegetation characteristics. Comparisons correspond to 10 percentage‐point increases in conifer, broadleaf tree, deciduous shrub, or evergreen shrub cover, a 10 m² ha⁻¹ increase in snag basal area, a 1 m² ha⁻¹ increase in legacy tree (>50 cm diameter) basal area, or a 100‐m increase in elevation. Points represent posterior medians, thick lines are 50% credible intervals, and thin lines are 90% credible intervals. Colors correspond to the proportion of posterior draws with estimates <0 (i.e., Bayesian p‐values).

FIGURE 4

Comparisons of multi‐stand richness (gamma diversity), rarefied to equal numbers of stands among groups. Gamma diversity represents the total number of species present across a collection of stands belonging to the same group and was calculated for categories of early seral conditions defined by stand age and disturbance type, and across all stand ages for a given disturbance type. Secondary panel headers indicate the number of stands used in rarefaction. Points and error bars represent posterior medians and 90% Bayesian credible intervals.

FIGURE 5

Comparisons of avian community composition among disturbance‐age categories. Points and error bars are posterior medians and 90% credible intervals of the mean Raup–Crick dissimilarity among all pairs of stands in the “reference group” (indicated by panel header) and each other disturbance‐age category (“comparison group”). Horizontal lines and shaded area indicate the posterior median and 90% credible interval of mean Raup–Crick dissimilarity among reference group stands.