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

Abstract

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% of contribution to the models). The seasonality of precipitation and distance from watercourses also have a significant impact. Assessment of potential reserves has identified the need for protected areas in southern China and points to the possibility of expanding reserves in Vietnam. The fact that river valleys are often densely populated can be an obstacle to the conservation of species.