Background/Question/Methods In the Madrean sky islands of the México-United States borderlands, restoration of fire-adapted ecosystems has the potential to contribute to multiple goals including protecting shared water resources, enhancing transboundary wildlife corridors, and creating and maintaining the flow and connectivity of ecosystem services. Our research investigates contemporary fire regimes of the Madrean sky islands and their relationship to climate conditions, human activities, and land management. To help inform regional, cross-boundary fire restoration planning, we analyzed 32-years of binational wildfire data (1985-2017) and evaluated variation in fire frequency and severity relative to historical fire regime characteristics derived from fire history literature. We assessed fire regime characteristics of nine major biotic communities and evaluated patterns across a range of land tenure classes and major climate gradients as represented by principal components (PC) analysis of twenty bioclimatic variables. The climate space provided a template for visualizing and comparing the distribution of fire regime characteristics in relation to vegetation types, and land ownership and tenure classes.
Results/Conclusions During the study period 335 fires burned 28% of the study area, with re-burns occurring on over 25% of the burned areas. The number of fires and burned area increased during the period, but fire frequency and acres burned were still far below historical norms. The greatest variation in fire regimes, including size, frequency, and severity was observed in places with the most diverse human activities and land uses – particularly in the mountain ranges adjacent near the international border. In both countries, composition of high severity fire was also closely related to climatic gradients. Average severity of recent fires was low despite some extreme outliers in cooler, wetter environments. Fire frequency was higher than historical in mesic Spruce-Fir forests, indicating effects of climate change that may shorten intervals for tree regeneration. In contrast, pine-oak forests in cooler and wetter environments in México burned with fire frequencies close to historical. Restoration of fire regimes will require binational cooperation aided by understanding where both the active use of fire, and indirect consequences of land management and climate change have altered the location and timing of fire. Natural protected areas, communal lands and private conservation lands will be critical to these endeavors.