Microclimate-based species distribution models in complex forested terrain indicate widespread cryptic refugia under climate change

Aim: Species’ climatic niches may be poorly predicted by regional climate estimates used in species distribution models (SDMs) due to microclimatic buffering of local conditions. Here, we compare SDMs generated using a locally validated below-canopy microclimate model to those based on interpolated weather station data at two spatial scales to determine the effects of scale and topography on potential future below-canopy warming and species distributions. Location: Great Smoky Mountains National Park (2,090 km²; NC, TN, USA). Time period: 1970–2006, late-century warming. Major taxa studied: Vascular plant species of Southern Appalachian forests. Methods: We compared the fit and spatio-temporal predictions of SDMs generated using occurrence records of 154 plant species and three climate models: macroclimate (1 km, WorldClim), downscaled climate (based on a 30-m digital elevation model), and fine-scale microclimate (30 m) from a below-canopy sensor network. Results: We found that, although SDM fit was similar across models, microclimate-derived SDMs predicted substantially greater species persistence with 4°C of regional warming, with a difference of 50% of the species pool in some areas. Microclimate models predicted that warming trends will be buffered in high-elevation and near-stream habitats. Microclimate SDMs predicted higher stability of mid-elevation species, particularly in thermally buffered areas near streams, and critically, less change in species composition at high elevation. In contrast, predictions of macroclimate and downscaled climate models were similar despite improved resolution. Main conclusions: Our results demonstrate that careful selection of climate drivers, including local near-ground validation rather than downscaling solely with elevation, is critical for projecting distributions. They also suggest that some species at risk from climate change might persist, even with 4°C of macroclimate warming, in cryptic refugia buffered by microclimate, pointing to the roles of forest cover and topography in explaining slower-than-expected changes in understorey communities. However, certain species, such as those currently occurring on low-elevation ridges that are sensitive to atmospheric changes, may be at more risk than macroclimate or downscaled climate SDMs suggest.