Defining large-scale arid island vegetation recovery targets through evaluating a reference ecosystem within an archipelago extent

Island ecological restoration presents challenges in establishing historical frames and reference ecosystems. Our study takes place in the Galapagos Islands and focuses on North Seymour (NS), recognized as a reference ecosystem for Baltra Island, which has suffered significant degradation. We assessed NS's arid plant community, comparing it with early twentieth-century records. A first survey identified that dominant woody species on NS include native Bursera graveolens, Cordia lutea, Castela galapageia, Parkinsonia aculeata, and Opuntia echios, while Cleome viscosa is the only exotic species registered. A second survey divided both islands into evenly distributed plots, recording adults and juveniles of the five dominant species from the first survey. NS showed a structured community with higher species richness and density compared to Baltra. Castela galapageia prevailed in disturbed areas on Baltra. Juvenile regeneration was scarce on both islands. NS exhibited high species richness throughout, while Baltra had only two areas with similar high richness. Co-occurrence analysis revealed significant associations between P. aculeata and B. graveolens on both islands. However, Baltra's network displayed missing links, indicating the need for restoration efforts. In conclusion, the structured plant community of NS can serve as one of the reference ecosystems needed for framing a restoration model for Baltra.