Are Australia’s volcanic-forests “biogeographic continental islands”?

This study investigates whether Cenozoic volcanic complexes in eastern Australia act as biogeographic islands, fostering high levels of terrestrial vascular plant endemism and range-restricted species compared to surrounding sedimentary landscapes. Over six million herbarium records were analysed to assess range-restriction using area of occupancy (AOO) and extent of occurrence (EOO). Georeferenced weighted endemism (GWE) identified centres of endemism, while random forest models explored the environmental drivers of range-restriction, incorporating climatic, topographic, and soil variables. Results indicate that species on volcanic lithologies were more range-restricted, with smaller AOO and EOO, compared to those on sedimentary units. Seventeen of the 31 volcanic complexes analysed exhibited greater species insularity than their surrounding landscapes. Volcanic complexes such as Atherton, Tweed, Glass House Mountains, and Tasmania were identified as key centres of endemism. Random forest models revealed that climatic and topographic factors, such as precipitation and terrain ruggedness, were stronger predictors of species distributions than volcanic lithology alone. The findings suggest that volcanic complexes in eastern Australia exhibit varying degrees of insularity, driven primarily by environmental conditions rather than the volcanic substrate itself. These volcanic ecosystems play critical roles in supporting Australia’s biodiversity, with broader implications for biodiversity conservation in isolated ecosystems globally.