Gap analysis of Firmiana danxiaensis, a rare tree species endemic to southern China

Firmiana danxiaensis (F. danxiaensis) is a special native species with a narrow distribution. More than 90 % of the plant species in the genus that F. danxiaensis belongs to are rare species with a narrow distribution. The main distribution area is Mount Danxia, a representative area of China Danxia where many endemic species of the Danxia landform have been bred. We carried out a gap analysis by overlapping the nature reserves with the potential habitat of F. danxiaensis. The results show that: (1) the potential habitat area of F. danxiaensis is 6,255.28 km(2) simulated by the Biomod2 ensemble model and 4,114.19 km(2) by Maxent, respectively, which accounted for 3.48 % and 2.29 % of the study area, located in Nanxiong county, Shixing county, Renhua county, and Qujiang county; (2) F. danxiaensis prefers areas with the max temperature of the warmest month over 32.5degree celsius, the temperature seasonality between 6000 and 7000, and the occurrence probability of F. danxiaensis was at its highest level when the max temperature of the warmest month reached between 36 and 37 degrees C, the temperature seasonality was nearly 7000; (3) more than 40 % of the potential habitat of F. danxiaensis was anthropogenically disturbed; (4) in the potential habitat simulated by Maxent, the conservation gap area is 3,390.26 km(2), accounting for 82.40 % of the total potential habitat, in the potential habitat simulated by Biomod2 ensemble model, the conservation gap area is 4.899.62 km(2), accounting for 78.33 % of the total potential habitat. The protection status of F. danxiensis is poor, with populations of F. danxiaensis in Yingde and Shixing not covered by nature reserves and already subject to serious human disturbance. It is recommended that the structure of existing protected areas be adjusted, the scope of corresponding nature reserves be appropriately expanded, and new nature reserves be added to ensure the sustainable development of F. danxiaensis populations.