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

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 (>35degree celsius) and in winter (<13degree celsius) 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 20degree celsius 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.

Automated summary

The iconic grass-trees of Australia, Xanthorrhoea semiplana, play a role in buffering ground-dwelling animals against extreme weather conditions, such as temperature and rainfall. The temperatures under the grass-tree canopies are more stable and have a smaller range compared to other areas, with a difference of up to 20 degrees Celsius cooler than the ambient temperature in summer. The largest grass-tree canopies provide the best shelter. However, the presence of the fungal pathogen Phytophthora cinnamomi and current burning practices can have detrimental effects on the survival of these trees and the wildlife that depend on them as shelter.