The importance of refuges in buffering landscapes against extreme heat events

Abstract

Refuges provide short-term relief from adverse situations and as such are mostly relevant for mobile fauna. For example, tree hollows may provide relief from heat waves. They therefore differ from microrefugia, which facilitate the long-term persistence of biota under environmental change by providing more stable conditions. Because extreme heat events are becoming more frequent, temperature refuges are important for conservation under anthropogenic climate change. Several microhabitats can considerably buffer extreme temperatures and may hence assist the persistence of biota. Here temperature buffering provided by three important microhabitats (tree hollows of Eucalyptus oleosa [Myrtaceae]; cavities formed by the leaves of the grass-tree Xanthorrhoea semiplana [Xanthorrhoeaceae]; inside the leaf-litter) during extreme heat events in the Mediterranean climate of South Australia is quantified. Each microhabitat significantly buffered against high temperatures and low relative humidity, compared to external sensors. They reduced daily temperature variation, cooling day temperatures by 1–5°C and warming night temperatures by 0.5–3°C on average. Maximum temperatures were up to 15.1°C lower. The buffering by microhabitats increased at a rate of 0.2-0.6°C per 1°C increase in ambient temperature, meaning that maximum buffering capacity was reached during the hottest periods. For tree hollows, the capacity to buffer temperature increased with depth, suggesting that old trees with deep hollows are important in facilitating the persistence of fauna during extreme weather events. Furthermore, greater canopy cover increased the amount of microclimatic moderation provided by the microhabitats. Our study highlights the importance of microhabitats and canopy cover in buffering extreme heat events. However, this is currently not considered in species distribution modelling under anthropogenic climate change nor in the management of vegetation.