Spatial heterogeneity of temperature across alpine boulder fields in New South Wales, Australia: multilevel modelling of drivers of microhabitat climate.

Understanding the spatial heterogeneity of temperatures across a region is significant for identification and protection of potential microhabitats for species conservation. However, this task is proving difficult because multiple factors drive the temperatures of microhabitats and their effect differs at different scales. In the Australian alpine region, boulder field habitats have been identified as important refugia for a range of small mammals. Vegetation cover and elevation have been found to drive thermal buffering at the level of single sampling sites within boulder fields, whereas the aspect and inclination of slopes have been found to affect thermal buffering at the level of clusters of boulder fields. But how the rock structure (number of rock layers, rock size and cavity of boulders) influences microclimate of boulder fields remains an open question. We used a multilevel modelling approach to detect the factors driving microhabitat temperatures in different seasons at different spatial scales in an Australian alpine region. We found that significant temperature differences existed within and between clusters of boulder fields in different seasons. Besides elevation and vegetation cover, the number of rock layers and rock cavity size also exerts important influences on extreme temperatures at the site (i.e. single boulder field) scale. Topographical variables such as slope gradient and elevation influenced minimum temperatures at the boulder field cluster scale. Variations in boulder field temperatures were significant at fine scales, with variations in minimum temperatures exceeding those of maximum temperatures. We suggest that variations in slope gradient and elevation, interacting with vegetation cover, the number of rock layers and rock cavity size can lead to fine-grained thermal variability, which potentially provides refugia for species at microsites, even when regional climatic conditions become less suitable for their survival.