The potential of sedimentary ancient DNA to increase our understanding of island ecosystem dynamics

Recent advances in sedimentary ancient DNA (sedaDNA) are transforming palaeoecological research and offer new opportunities to study biodiversity change on islands. We assess the potential of sedaDNA for reconstructing long-term ecological patterns by evaluating current island studies worldwide. We map geographic representation across the floras of 134 archipelagos and islands in relation to the availability of reference data for the P6 loop of trnL (UAA) intron, the most widely used marker in ancient plant DNA metabarcoding. Our analysis highlights substantial geographic and taxonomic biases, with temperate and tropical islands, regions of particularly high biodiversity, remaining comparatively underrepresented both in sedaDNA studies and in species-level DNA reference databases. These patterns identify clear priorities and opportunities for expanding reference libraries and improving the global applicability of sedaDNA approaches. Nevertheless, our database assessment indicates that when taxonomic reference coverage is relatively complete and depositional conditions are favourable, sedaDNA can provide high-resolution species and trait information. This is exemplified by Lake Torfdalsvatn (Iceland), where adequate reference representation and sedaDNA preservation enables clear detection of declines in Betula and Juniperus following Norse settlement and sheep introduction, as well as trait-based shifts toward vegetation adapted to disturbance, increased aridity, and high light conditions.