From drying to frying: drought and fire as interacting drivers of vegetation change in piñon-juniper-oak forests of the Chisos Mountains, Big Bend National Park, USA

Abstract Background Piñon-juniper forests provide important habitat, cultural resources, and ecosystem services across western North America, but increasingly severe droughts and wildfires threaten their persistence. Understanding responses to successive disturbances is critical because wildfire may affect forests already transformed by drought. We used 20 years of permanent-plot data from the Chisos Mountains, Texas, to quantify forest changes in response to a severe drought and subsequent wildfire. Results Drought caused widespread declines in tree density and basal area. In unburned plots, both declined by approximately 50% between the pre-disturbance and post-drought censuses, with little subsequent change. Fire caused additional but spatially variable mortality that ranged from limited tree death to near-stand replacement. High-severity fire plots had already lost 70.7% of tree density after drought and retained only approximately 75 trees ha⁻ 1 after the subsequent fire and cumulative basal-area loss reached 92%. Piñon declined by approximately 99% in these plots, compared with 92% for junipers and 89% for oaks. Mortality was not concentrated in particular tree sizes. Fire also significantly reduced juvenile tree abundances. Conclusions Successive drought and fire created a heterogeneous mosaic of drought-thinned forests and burned patches. As these disturbances become more common, forest persistence may depend on recovery between disturbances rather than resilience to either disturbance alone.