Australia’s iconic grass-trees, locally known as yaccas, have long been admired for their hardiness and elegance. However, a new study has unveiled an astonishing characteristic of these plants: their vital role in protecting wildlife from extreme weather conditions.
These grass-trees (Xanthorrhoea semiplana sub species semiplana) are no ordinary plants. They’re equipped with long, thick, and dry grassy skirts that not only act as a natural insulation against lethal temperatures but also serve as an effective umbrella.
According to the research carried out by the University of South Australia and Kangaroo Island Research Station, temperatures under the grass-tree canopies were found to be up to 20 degrees cooler during the scorching summer days. Conversely, in winter, the shelter provided by the grass skirts offers significantly warmer conditions at night.
Furthermore, the older yaccas possess a distinctive feature: the ability to keep the soil beneath them entirely dry under 80 percent of their expansive canopies during prolonged periods of heavy rain. This offers a dependable refuge for many animals, particularly during the wet season.
Lead researcher Dr Topa Petit said it’s not surprising that many creatures seek shelter under yaccas, particularly the older species with the largest and thickest skirts.
“Several of the 29 species of Australian grass-trees are known to host native bush rats, threatened bandicoots, echidnas and pygmy-possums, among other wildlife,” said Dr. Petit.
“Temperatures over 40 degrees can be lethal to some of our wildlife, but grass-trees provide extremely stable temperatures with very little variation.”
“The remarkable ability of these grass-trees to protect wildlife from deadly climatic extremes – as well as providing effective hiding spots from predators – strengthens the mounting evidence that these plants are keystone species.”
However, the yaccas on the mainland and Kangaroo Island are facing multiple threats which could have dramatic consequences for wildlife, noted Dr Petit.
One such threat is the soil pathogen Phytophthora cinnamomi, which has been causing extensive dieback among the grass-trees. Additionally, fuel reduction programs, summer fires, and land clearing are exacerbating the plight of these vital plants.
“Grass-tree resilience to bushfires appears to be overestimated,” said Dr. Petit. “Moreover, even if grass-trees are not killed by fires, their very old thick skirts of dead leaves burn, leaving no shelter to animals in post-bushfire environments.”
In 2022, the Federal Government added fire regimes that cause declines in biodiversity to the list of Key Threatening Processes.
“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 noted that after yaccas are scorched by fire, it can take decades to regain their role as effective shelters and they become more susceptible to Phytophthora infestations.
“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.”
Beyond the recent findings about their role in shielding wildlife from extremes, yaccas have always been an integral part of the Australian ecosystem. Their flower spikes provide food for nectar-feeding birds and insects, while the dense skirts of their older leaves offer shelter for various ground-dwelling animals.
Grass-trees, or yaccas, have a distinct appearance. They feature a stout, often blackened trunk, topped with a crown of long, slender, and arching leaves. Depending on the species and age, some grass-trees can reach heights of up to several meters.
One of the most striking features of the yacca is its flowering spike. These can be very tall, sometimes over 3 meters in length, and are densely packed with small, white flowers. The spikes are a rich source of nectar and attract various pollinators.
Yaccas have evolved in Australia’s fire-prone environments. Their trunks are fire-resistant, and in many species, fire stimulates flowering. After a fire, the yacca can regenerate from its base using stored nutrients.
Grass-trees grow very slowly. It can take several years for them to grow just a few centimeters. Older specimens with tall trunks represent many decades, if not centuries, of growth.
Indigenous Australians have found various uses for the grass-tree. The resin from the plant has been used as an adhesive for tools, while the flowering spike, when soaked in water, can produce a sweet drink.
While many species of yaccas are still widespread, their habitats face challenges from land clearing for agriculture and urban development, as well as diseases like the previously mentioned Phytophthora cinnamomi.
The research is published in Pacific Conservation Biology.