The role of grass-tree Xanthorrhoea semiplana (Asphodelaceae) canopies in temperature regulation and waterproofing for ground-dwelling wildlife

Abstract

Context The iconic grass-trees (Xanthorrhoea semiplana) of Australia are used by many animal species, but their role as shelters against weather extremes is poorly known. The severe contribution of the fungal pathogen Phytophthora cinnamomi to grass-tree deaths and current burning practices could affect small animal conservation by exacerbating impacts of weather extremes. Aims We examined the buffering role of X. semiplana canopies against extreme weather at four sites in the Mount Lofty Ranges, South Australia. Methods We measured ambient temperature, temperatures under grass-tree canopies, and 2 m away at random locations in summer (>35°C) and in winter (<13°C) over 24-h periods at each study site. We scored soil dryness under the canopies during and after heavy rainfall. Key results Temperatures under grass-tree canopies were more stable and with smaller ranges than other temperatures, and showed dramatic differences in summer when conditions were up to 20°C cooler than ambient. Temperatures were higher under grass-trees at night in winter. The soil under the largest canopies was completely dry during and after heavy rainfall. Conclusions Xanthorrhoea semiplana buffers ground-dwelling animals against temperature extremes and rain so that the animals maintain their thermal resistance. Animals may choose foraging times based on grass-tree availability. The largest grass-trees provide the best shelter. Implications Considerable grass-tree deaths from P. cinnamomi infestation, together with removal or burning, can have dramatic detrimental consequences for their habitat value and the survival of wildlife using them as shelter.