Habitat suitability evaluation for eight ancient tree species on Hainan island under climate change

This study aims to evaluate the distribution of the potential suitable habitats of eight ancient tree species on Hainan island under climate change and their responses to environmental factors, and to provide a reference for the management and protection of ancient trees on Hainan island.

Taking eight ancient tree species with a tree age of≥300 years on Hainan Island as the research objects, relevant environmental variables were screened out. The MaxEnt model was used to predict the changes in the potential suitable habitats and the key influencing factors of these eight ancient tree species under current and future climate conditions.

1) The average training AUC values of the eight ancient tree species are all above 0.9, indicating extremely high prediction accuracy. 2) Population density is an important influencing factor for the suitable distribution of many ancient tree species, and the contribution rate and permutation importance value of this factor are relatively high. Different ancient tree species are also jointly affected by their respective specific climate, soil and other factors; 3) Under the current climate conditions, Ficus virens and Bischofia javanica have the widest suitable habitat ranges on Hainan island, approximately 20 248.36 km² and 16 367.39 km² respectively. The suitable habitat areas of Mangifera indica and Tamarindus indica are relatively narrow among the eight ancient tree species; 4) Under the future climate scenarios, the areas of potential suitable habitat change for ancient trees are basically centred on the edges of the original suitable habitat areas. Areas of high loss, gain and turnover of ancient trees are mainly concentrated in coastal cities and counties in the northeast and southwest of Hainan island.

The response of eight species of ancient trees on Hainan island to climate change can be better simulated using the optimized MaxEnt model. Human activities and the natural environment have a combined effect on the long-term survival of ancient trees. The results can provide scientific reference for the sustainable conservation of Hainan's ancient tree resources.