Species distribution models (SDMs) have rapidly evolved into one of the most widely used tools to answer a broad range of questions in ecology, from the effects of climate change to challenges for species management. Current SDMs and their predictions under anthropogenic climate change are however often based on free-air or synoptic temperature conditions with a coarse resolution, and thus fail to capture apparent temperature (cf. microclimate) experienced by living organisms within their habitats. Yet microclimate operates as soon as a habitat can be characterized by a vertical component (e.g. forests, cities, or mountains) or by horizontal variation in surface cover. The mismatch between how we usually express climate (cf. coarse-grained free-air conditions) and the apparent microclimatic conditions that living organisms experience has only recently been acknowledged, yet several studies have already made considerable progress in tackling this problem from different angles. Here, we use the results from a series of experimental and observational studies in mountain regions worldwide (in the framework of MIREN, the Mountain Invasion Research Network) to show the importance of physiographic, biophysical and anthropogenic processes in shaping microclimate, and the resulting effects of microclimate on plant species distributions.
Results/Conclusions
We used a global network of temperature loggers in mountain road- and trailsides to show how topography, vegetation cover and disturbance influence microclimatic variability in mountains, and compare patterns in microclimate obtained through different techniques (cf. In-situ measurements, interpolation and statistical downscaling). We then illustrate the effect of integrating microclimate into SDMs, showing that warm-adapted lowland species use warmer microclimatic hotspots as stepping stones towards higher elevations, while cold-adapted high-elevation species can use cooler micro-environments as refugia. Additionally, using seed-addition experiments along elevation gradients and on north- and south-facing slopes above their current range limits (cf. microclimatic gradient), we tested the establishment of six non-native species with a lowland origin under experimentally enhanced anthropogenic pressures (disturbance, added nutrients and increased propagule pressure). Both the large microclimatic variability in temperature as the anthropogenic pressures, and the interaction between both, had profound effects on establishment, growth and overall success of the study species.