Risk assessment of habitat suitability decline for the endangered riparian tree Pterocarya tonkinensis (Juglandaceae): conservation implications

Tonkin wingnut is the rarest species within the relict tree genus Pterocarya (Juglandaceae), known from only a few isolated stands in the Indo-Burman hotspot. Despite its classification as a vulnerable species, Pterocarya tonkinensis has received comparatively less attention than other wingnut species, leading to a limited understanding of its distribution patterns. In this study, we utilize spatial distribution modeling with MAXENT software and conservation prioritization methods implemented in ZONATION to estimate the potential range of species, identify the key environmental variables influencing its habitat, and designate potential areas for conservation. We used a set of 45 known species populations, the set of bioclimatic variables, and the proximity of watercourses to create the model of the potential range. The results indicate two main centers of potential climatically suitable areas for the species in the future - in southern Yunnan (China) and Vietnam. The calculated total suitable area (292,365.67 km2) is similar to the estimated extent of species occurrence but may decline in the future. Highly suitable areas near the rivers cover around 19,000 km2. The most important factors shaping species occurrence were those related to temperature amplitude (around 60