Functional redundancy shapes spatial patterns of vulnerability to climate-driven shifts in plant communities across Australia

Climate change threatens plant communities worldwide with substantial species losses, yet the consequences of reduced diversity for ecosystem functioning remain uncertain. Functional redundancy, where multiple species fulfil similar ecological roles, may provide functional insurance by buffering ecosystem processes against species loss. Here, we combined plant composition data from 646 TERN AusPlots with gap-filled trait data (maximum plant height, leaf mass per area, and seed dry mass) from the AusTraits database to deliver the first continental-scale assessment of functional redundancy in Australian plant communities. By explicitly examining diversity metrics and functional redundancy across biomes, we assessed functional vulnerability and buffering capacity under climate change. We estimated potential impacts of species loss under future climates using community thermal and aridity tolerances relative to projected climate exposure. We analysed the continental distribution of functional redundancy (reflecting competitive ability, resource acquisition strategies, and dispersal-establishment trade-offs), projected climate-driven compositional change, and relationships with bioclimate to identify vulnerable native communities. Our results revealed strong latitudinal gradients in climate-change impacts, with tropical northern communities facing greater risk of compositional change as future hotter and drier conditions become unsuitable for monsoon-dependent species. Functional redundancy of current vegetation communities increased toward central Australia, aligning with increasingly stressful (hotter, drier) bioclimates. At the biome scale, Mediterranean and arid communities exhibited higher functional redundancy and lower climate risk due to shared 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 southern Mediterranean regions of South Australia and Western Australia. Conservation and monitoring efforts should prioritise these regions. Our findings highlight how local bioclimate influences functional redundancy and future climate-change-driven vulnerability, providing a spatial framework to support biodiversity monitoring, policy and land management across Australia.