Effect of Fire History on Nonbreeding Bird Communities in a Giant Sequoia Forest (Sequoiadendron giganteum)
- O'Hearn, Karyn C
- Advisor(s): Hahn, Thomas P
Despite birds being heavily studied members of forest communities, few generalities exist regarding species response to fire. Further, there very few studies of bird communities outside the breeding season. Quality of nonbreeding habitat is critically important to migrants, local transients, and wintering species, and changes to nonbreeding habitats can have important consequences for communities across seasons. In 2015, the Rough Fire burned part of the Grant Grove sequoia forest within Sequoia Kings Canyon National Park (SEKI) in areas with different fire management histories. Subsequently, SEKI deployed acoustic recording units (ARUs) at nine stations in five sites in areas with (prescribed and wildfire) and without prior fire management activities (old growth and second generation mature forest). The aim of this study was to test the effects of these fire histories on nonbreeding community composition by quantifying and comparing species richness and composition in fall and in winter. A secondary aim was to determine the efficacy of manually detecting winter species from surveys of nonbreeding-season recordings. Random 10-minute samples were manually surveyed from each point recording six times September 2017 – Februrary 2018 for a total of 540 minutes surveyed. Differences in richness and composition between fall and winter were analyzed by site type and sites organized into fire history categories. Richness was evaluated with a general linear mixed model and a Poisson regression with fixed factor effects to test for significance. Differences in species composition were compared and tested with non-metric multidimensional scaling (NMDS) using a community-by-species matrix. Frequency was examined to evaluate individual species contribution to composition. There were 45 total species detected, 22 across both seasons. Winter season had significantly lower species richness (ß = -0.88, p < 2e-16) than fall. The second generation mature forest (ß = -0.4, p = 0.033) and the site burned during the Rough Fire (ß = -0.3, p = 0.09) both had significantly lower species richness in winter. The prescribed fire history category had significantly greater species richness (ß = 0.37, p = 0.002). Species richness was also significantly higher at sites with increasing numbers of prescribed fires (ß = 0.12, p=0.0023). Species composition was more similar in fall than in winter. There were significant differences in species composition among all sites (r2=0.80, P=0.02) and for three of the five fire-associated categories in winter: sites with and without fire history (r2=0.4, P=0.01), with different time since fire (r2=0.52, P=0.01), and increasing total number of prescribed fires (r2=0.86, P=0.01). Differences among sites grouped by prescribed fire or wildfire did not significantly correlate with species composition. Overall, this study indicates that fire history positively affects winter bird communities, and demonstrates that acoustic recordings are effective in detecting winter species. This baseline investigation will benefit SEKI’s efforts to understand how to best use these long-duration recordings for examining relationships between species and habitat, and future studies of how fire histories affect winter communities. Understanding the differences in these avian communities can assist land managers in protecting associated birds in fire-prone landscapes across all seasons.