Background/Question/Methods Effective conservation and management responses to mega-disturbance events and potential ecological transformation requires understanding variability in how vegetation and wildlife species are responding to these threats at multiple scales across broad contexts of climatic gradients and fire regimes. The Madrean sky islands provide a unique study area for addressing this challenge, where biogeographical location and elevational gradients interact to produce a globally recognized biodiversity hotspot. Our objective was to link multi-scale bird and vegetation responses to fire regimes across four sky island mountain ranges to assess factors and mechanisms that drive vulnerability and resilience. Field observations for birds and vegetation were collected from four mountain ranges (n = 335) between 2010 and 2015. The samples represented variability across climatic gradients: Aconchi sites were located in the warm, dry extreme, relative to the Ajos and Huachuca sites mid-way along the gradient; the Chiricahuas were in cooler, wetter environments. Fire history at study sites included unburned areas (fire data time frame 1985-2017); and locations that had burned up to three times. We modeled relationships between vegetation, fire and climate metrics and overall avian richness (alpha diversity) and similarities/differences in avian species composition (beta diversity) using multi-species occupancy models and multivariate ordination.
Results/Conclusions Vegetation and bird communities found in mesic environments at higher elevations and latitudes reflected increased fire frequencies and high severity fire in mixed conifer and spruce-fir forests. Specifically, we observed beta diversity differences in these areas, especially with birds that rely on old growth forests. In contrast, fires were absent or infrequent in some pine-oak forests, oak woodlands, and grasslands, especially in the warmest, driest environment across the four mountain ranges. These vegetation communities historically relied on frequent fire to maintain sustainable structure and function, and impacted bird diversity, especially beta diversity with species that rely on frequent fire or structures such as snags and vegetation openings often created by fire. In these warmer, drier environments, land-use change and management or restoration activities are important drivers of change. Birds are often used as ecological integrity indicators based on their reliance on forest structure for foraging and nesting. By understanding avian biodiversity drivers, we ultimately gain insights on ecosystem sustainability among multiple stressors, which is relevant to goals among diverse stakeholders in this binational region. Our study across both latitudinal and elevation gradients provides a unique opportunity to evaluate potential future climate and fire responses, allowing for evaluation of adaptive strategies.