Non-native plant species on inselbergs of Brazilian tropical forests: checklist and insights for biodiversity management and conservation

The invasion of non-native species into spatially restricted habitats with unique plant communities poses a major challenge to biodiversity conservation. Inselbergs, granitic and/or gneissic outcrops with distinct abiotic conditions, host highly specialised plant species, but are increasingly threatened by the colonisation of exotic plants. This study aimed to: (1) compile the first comprehensive checklist of non-native plant species on inselbergs in two Brazilian phytogeographic domains: Atlantic Forest (AF) and Caatinga (CA), with a focus on identifying the invasive species; (2) analyse domain-specific associations of non-native species; (3) evaluate whether specific life forms of non-native species are associated with a particular domain; and (4) propose future research directions and management strategies. We documented 99 non-native species across AF (71 spp.) and CA (54 spp.) inselbergs using data from public online databases and published literature, of which 33 (33.3%) were classified as invasive. Therophytes were significantly associated with CA inselbergs and chamaephytes with AF inselbergs, reinforcing that certain life forms amongst non-native species exhibit domain-specific affinities, likely reflecting adaptations to contrasting environmental conditions. The findings of this study reveal that non-native species are widespread across inselbergs in both analysed domains, with many of them being invasives, underscoring the urgent need for early intervention. Future studies should concentrate on linking functional traits to invasion patterns in inselbergs, as well as integrating biogeographic and phylogenetic information, which will be crucial to anticipating and mitigating the spread of invasive species in these vulnerable environments.