Seeing the forest through the trees: Applications of species distribution models across an Australian biodiversity hotspot for threatened rainforest species of Fontainea

Southern Fontainea (Fontainea australis) and Coastal Fontainea (F. oraria) are two closely-related, rare plant species endemic to the subtropical rainforests of central, eastern Australia. Both species have threatened conservation status, with their contemporary and projected distribution poorly known. We aimed to use species distribution models (SDMs) to identify (1) the potential range under current conditions, (2) suitable habitat area conserved in protected areas and (3) responses under future environmental conditions of the species. Using a presence-pseudo-absence approach, and a set of bioclimatic variables, combined with topographic factors, we modelled the spatial dynamics of Southern Fontainea and Coastal Fontainea. We present comparisons among regression (GLM) and Random Forest (RF) SDMs for current and projected future conditions under low (SSP 1-2.6) and high (SSP 5-8.5) emission scenarios for the period 2081-2100 from an ensemble of three CMIP6 climate models. On-ground surveys verified the contemporary distribution of Southern Fontainea across the study extent. GLM-and RF-based models identified similar areas of suitable habitat under current conditions, but both models indicated that less than half of the suitable Southern Fontainea habitat is under protected tenure. GLM-based SDMs suggest an expansion of suitable areas of Southern and Coastal Fontainea under both low-and high-emission climate projections. By contrast, RF-based SDMs indicated a moderate increase of suitable habitat under future climate projections. The steep slopes and gullies of the mountain ranges, which span the Queensland and New South Wales border of central, eastern Australia, seem likely to provide long-term, stable climate refugia for Southern Fontainea. Models generated under current conditions identified novel areas that could support undiscovered populations of Southern and Coastal Fontainea. These findings have significant conservation implications for the critically endangered Coastal Fontainea, which is projected to lose suitable habitat under a high-emission climate scenario.

Automated summary

Southern Fontainea and Coastal Fontainea are rare plant species endemic to the subtropical rainforests of central, eastern Australia. Their conservation status is threatened, and the distribution of these species is poorly known. This study used species distribution models to assess the present and future distribution and conservation of the two species. The models indicate potential expansion of suitable habitat for Southern and Coastal Fontainea, with the mountain ranges serving as climate refugia. However, the critically endangered Coastal Fontainea is projected to lose suitable habitat under high-emission climate scenarios.