Fire authorities urged to avoid yaccas during burn-offs

South Australian researchers want grass-trees shielded from burn-offs, saying they should be considered keystone species which are critical to the environment.

A recent study by a team of researchers in South Australia (SA) has shown the grass-tree – also known as yacca – can buffer ground-dwelling animals from rain and temperature extremes.

The researchers from the University of SA  and Kangaroo Island Research station measured temperatures under the grass-tree (Xanthorrhoea semiplana spp. semiplana) canopies at four sites across the Mt Lofty Ranges to the east of SA’s capital, Adelaide.

The buffering role of the canopies was strong in summer with temperatures under the grassy skirts up to 20 degrees cooler than nearby shaded areas.

The researchers suggest this difference could be critical in an area where summer temperatures can exceed 40 degrees.

“Temperatures over 40 degrees can be lethal to some of our wildlife, but grass-trees provide extremely stable temperatures with very little variation,” says lead researcher Dr Topa Petit.

The grass-trees also modulated the cold extremes — temperatures were consistently higher under the grass-trees at night in winter compared to ambient temperature. The researchers suggest that this stability in temperature may help with the maintenance of torpor in some species.

Soil samples were also taken from under the grass-tree skirts. Not surprisingly, the sampling showed a strong link between canopy cover and soil dryness, with the largest canopies keeping the soil below completely dry during and after heavy rainfall.

The study, published in Pacific Conservation Biology, contributes to the mounting evidence for some grass-trees to be declared “keystone species.”

A keystone species has a disproportionate effect on an ecosystem in relation to its population size to the extent that its removal or decline could result in the destruction of the ecosystem.

Petit says however, the yaccas on the mainland and Kangaroo Island are facing multiple threats which could have dramatic consequences for wildlife.

“Historically, grass-trees were cleared for agriculture. They are now cleared or burnt in so-called fuel reduction programs. Extensive research has shown that this practice increases fuel loads and dries out the landscape.”

Dr Petit says yaccas scorched by fire can take decades to regain their role as effective shelters and are more susceptible to infestation by Phytophthora, a fungal pathogen that’s causing widespread dieback of grass-trees.

“It’s important that habitat management be backed by sound research and scientific monitoring rather than hysteria. We owe it to the future of our ecosystems.”