From Drying to Frying: Drought and fire as drivers of vegetation change in piñon-juniper- oak forests of the Chisos Mountains, Big Bend National Park, USA

Background Piñon-juniper (PJ) forests and woodlands comprise cover vast portions of western North America, providing habitat and food to myriad species. Increasing drought and wildfire activity from climate change and fire suppression are triggering major changes in forest structure and composition in PJ systems, yet we know little about how these recent disturbances coincide or diverge from historical disturbance regimes. In an effort to fill this gap, we evaluated 20 years of forest change data from the Chisos Mountains, Texas to evaluate trends in piñon-juniper forest dynamics in response to a record 2011 drought and subsequent 2021 wildfire. Results Our results revealed that the Chisos Mountains have experienced recent, range-wide tree mortality over the last two decades, in response to drought and subsequent fire, especially within high-severity fire sites. The 100 sample plots in our study experienced approximately 56% survivorship over the pre-disturbance to post-drought sampling interval, demonstrating the major impact of the 2011 event on forest stand dynamics. Sites that experienced high-severity fire in the 2021 South Rim 4 Fire displayed even further significant losses in tree density and basal area in response to stand-replacing fire after the drought. Low- to moderate-severity fire sites remained relatively unchanged after the fire. High-severity sites experienced an average of just 14% survivorship from the post-drought to the post-fire sampling interval, which highlights the stand-replacing nature of the South Rim 4 Fire within high-severity burn patches. Conclusions We suggest that droughts and contemporary fires like the 2021 South Rim 4 Fire might have been a natural part of this regions’ fire regime prior to Euro-American settlement. Drought and wildfires in the wake of drought are becoming increasingly common throughout the region as the impacts of climate change continue to amplify, and studies like this are important for elucidating how contemporary wildfires are concordant with or diverge from historical fire regimes for sustainable PJ ecosystem management in the Anthropocene.