Limited impact of microtopography on alpine plant distribution

Complex topography regulates near-surface temperature above the treeline. It may thus sustain microrefugia for alpine plants and relax the need of shifting upward when the climate warms. The effectiveness of these microrefugia rests on the premise that plant distributions in alpine landscapes are mainly controlled by fine-scale topographic variation. We tested this assumption by relating the distribution of 79 plant species and 10 community attributes across 900 1 m² plots in a landscape spanning 1677 m of elevation to 17 topographical descriptors at resolutions between 1 and 301 m. We found that the presence of most species and most community attributes were better explained by topographic variation at coarser scales (> 20 m). Fine-scale topography is more clearly reflected in moisture than in temperature requirements of species. The elevational gradient rather than topographic variation at any scale, is the single most important driver of both species distributions and the variation in community attributes in the area studied. We hypothesise that our results reveal a hitherto underestimated influence of spatial mass effects on alpine plant distributions. These effects can override environmental filtering at fine scales and will thus impede the survival of cold-adapted plants in small and fragmented refugia under climate warming.