Old and Valuable Trees of Wuzhishan, a Tropical City in Hainan, China: Distributional Patterns and Their Drivers

Old, valuable trees (OVT) comprise an important urban ecological and cultural resource. Understanding their innate traits and driving factors can facilitate management, conservation and ecotourism development. This study assessed relationship between the species diversity composition, distribution, growth status, and tree-habitat of OVT in Wuzhishan City in Hainan Province, south China. We acquired tree and site data by field surveys, literature mining, interviews and laboratory tree-age determination. The results show that there are 216 OVT in Wuzhishan City, belonging to eight families and 13 genera and 21 species. Sapindaceae was the family with the largest number of species (79). Lychee was the predominant genus represented by Litchi chinensis . The overall age structure of OVT in Wuzhishan City is pyramidal, mainly concentrated in the range of 100-299a (average 163a). According to the grading norms of Chinese OVT, there are three Grade 1, 21 Grade 2 and 192 Grade 3 OVT. Tree height, trunk girth and crown width were normally distributed, mainly concentrated at ten-19 m (mean 32.1 m), 300-499 cm (mean 423 cm) and ten-20 m (mean 17 m), respectively. The overall number of individuals of OVT in Wuzhishan City was evenly distributed. The results of General Linear Model (GLM) analysis showed that the tree height of OVT in Wuzhishan City was highly significantly correlated with precipitation of wettest month (P=8.69E-04), trunk girth was highly correlated with annual mean temperature (P=9.30E-04) and precipitation of coldest quarter (P=3.06E-04), crown width was significantly correlated with mean temperature of warmest quarter (P=8.28E-03). The number of OVT in Wuzhishan City was significantly or highly significantly correlated with most environmental factors. In conclusion, Wuzhishan City has a rich variety of OVT with a uniform distribution; environmental factors have a greater impact on OVT, and it is recommended that targeted protection measures for OVT be developed in conjunction with the actual situation of the city.