Functional redundancy buffers plant communities against climate-driven shifts in composition

Irene Martin-Fores , Rhys Morgan, Samuel Andrew, Rachael V. Gallagher, Greg R. Guerin

Climate change threatens plant communities worldwide with significant species losses, yet the consequences of reduced diversity for ecosystem function remain uncertain. Functional redundancy—where multiple species fulfill similar ecological roles—may act as ‘functional insurance’ by buffering ecosystem processes against species loss. Here, we combined plant composition data from 646 TERN AusPlots with gap-filled trait data (i.e. maximum plant height, leaf mass per area, and seed dry mass) from the AusTraits database to provide the first continental-scale assessment of functional redundancy in Australian plant communities. We estimated the potential impact of species losses under future climates based on community thermal and aridity tolerances relative to projected climate exposure. We examined the continental distribution of functional redundancy (in terms of competitive ability, resource acquisition strategies, and dispersal-establishment trade-offs in reproductive strategy), projected climate-driven compositional changes, and their relationship to bioclimate to identify vulnerable native communities.
Our results revealed strong latitudinal gradients of climate-change impacts on Australian plant communities, with those in the tropical north exposed to greater threat of changes in community composition because of future hotter and drier conditions not being unsuitable for monsoon-dependent species. Functional redundancy increased toward central Australia, aligning with more stressful (hotter, drier) bioclimates. At the biome scale, Mediterranean and arid communities showed higher functional redundancy and lower climate risk due to functional similarity in drought-adapted traits. Future rainfall changes were the dominant driver of climate-induced shifts in plant community composition.
The most vulnerable communities—at highest risk of functional destabilisation—were located along the northern coastline, with additional hotspots in the southernmost parts of the Mediterranean regions of South Australia and Western Australia. Conservation and monitoring efforts should prioritise these areas. Our findings highlight the influence of local bioclimatic factors on functional redundancy and the need to understand these dynamics to better forecast ecosystem resilience under ongoing climate change, while providing a spatial framework to guide biodiversity monitoring, policy, land management and conservation action across the Australian continent.