Climate Refugia for Pinus Spp. In Topographic and Bioclimatic Environments of the Madrean Sky Islands of México and the United States 

Abstract ContextRefugia are island-like habitats that are linked to environmental stability. Where topography acts as a deterministic control, microrefugia may continue to function as habitat under reduced rates of climate change. Continental island ecosystems provide propitious settings for identifying patterns of refugia at multiple scales and applying that knowledge to conservation. Objectives Our main objective was to identify microrefugia for pines where habitats are defined by topographic heterogeneity. Secondary aims were to describe climatic variation within microrefugia and examine how species’ response to seasonal climate alters spatial predictions of microrefugia. Methods We investigated how topography forms microrefugia in the Madrean sky islands, located in the borderlands of México and the United States. Our design incorporated pine species presence and absence field observations (P. strobiformis, P. engelmannii and P. chihuahuana, P. arizonica and P. discolor), modeled in relation to terrain, bioclimatic and remote sensing predictors. Results Terrain ruggedness, slope position and aspect defined microrefugia for pines within specific elevation ranges. Some species had narrow habitat preferences (e.g., P. chihuahuana); others exhibited a broader range of tolerance (e.g., P. arizonica). Hotspots of microrefugia were either limited to northern islands or occurred across central or southern latitudes. Response to seasonal climates shifted distributions of hotspots for species with open canopy structure and where regular fires occur. ConclusionsPine habitats with greater climate stability may provide holdouts and stepping-stones critical to species persistence with future change. Networks of refugia provide a promising focus for conservation, restoration, and fire management across a diverse, binational region.