Microclimates provide small-scale variations in the conditions experienced by plants and arise due to topography (e.g. aspect) and structure-forming species (e.g. shrubs, cushion plants). These topographic and biotic microclimates have consequences for community composition and trait distributions, but how they interact is unclear. As shrubs continue moving uphill into alpine ecosystems, it is critical to understand the potential for shrubs to influence microclimates and the resulting patterns of biodiversity, and how that influence varies across topographically complex alpine landscapes. Here, we ask 1) how are shrub microclimates mediated by topography and 2) how does the trait distribution of plant communities shift when growing in the presence of shrubs. To address these questions, we established 108 plots across a north (N)- and south (S)-facing aspect at Niwot Ridge in the Front Range of Colorado, half of which were placed on the leeward side of a shrub while the other half were paired plots outside the influence of shrubs. During the growing season we deployed iButtons for continuous soil temperature data, measured soil moisture every other week, assessed species composition, and used a comprehensive database of traits collected at Niwot Ridge to address the trait distribution of these communities.
Results/Conclusions
Shrubs buffered soil temperatures on S-facing aspects, decreasing mean and maximum temperatures. Additionally, regardless of aspect, shrubs increased minimum temperatures and growing degree hours. Across both aspects, shrubs increased early growing season soil moisture, likely due enhanced snow accumulation that delayed meltout. Through modifying these microclimatic conditions, shrubs fostered plant communities that were taller, had higher leaf area, and had lower leaf dry matter content regardless of aspect. Protection from wind, greater water availability early in the season, and higher minimum temperatures may be driving the assembly of more resource acquisitive species. These findings suggest that shrubs may act as microrefugia in a changing climate due to the buffered microclimate they provide and the less stress-tolerant traits that they foster.