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 rare habitats with unique plant communities represents a significant challenge to biodiversity management and conservation. Inselbergs, granitic and/or gneissic rocky outcrops, typically exhibit distinct abiotic conditions compared to the surrounding matrix and host a diverse array of highly specialized plant species. However, these unique ecosystems are increasingly threatened by the colonization of non-native plants, jeopardizing their biodiversity. 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) analyze 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 and CA inselbergs using data from public online databases and published literature. Among these, 33 species (33.33%) were classified as invasive species. Angiosperms (95 spp.) dominated the records of non-natives, followed by ferns (two spp.), lycophytes (one spp.), and bryophytes (one sp.). On the CA inselbergs, 54 non-native species were identified, mainly Poaceae (18 spp.) and Asteraceae (eight spp.). On AF inselbergs, 71 non-native species were documented, with Poaceae (11 spp.) and Fabaceae (seven spp.) as leading families. Therophytes were significantly associated with CA inselbergs and chamaephytes with AF inselbergs, reinforcing that certain life forms among 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 analyzed 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.