Venerable trees of tropical Chinese Wuzhishan city: Distribution patterns and drivers

In this study, we investigated the relationships among species composition, diversity, distribution, growth status, and habitats of venerable trees (VTs) in Wuzhishan City, Hainan, China. VT are defined as venerable tree. VTs bear witness to changes in human society and culture; VTs that once occurred in open or forested areas are now often surrounded by or adjacent to new infrastructure and urban development. In spite of urban development, protecting VTs is important for preserving the history they contain as a part of their carbon sequestration, maintaining their unique ecological services, and continuing to appreciate and advance their cultural symbolism and meaning. We studied VTs and their habitats based on literature reviews, field surveys, interviewing local people, and tree-age determination in the laboratory. Our results revealed 216 VTs in Wuzhishan City of 100 or more years old, belonging to nine families, 13 genera and 21 species. Among families, Sapindaceae comprised the largest number of VTs with 79 species and was especially represented by the fruit tree, Litchi chinensis Sonn (Lychee). Perhaps unsurprisingly, we also found that older VTs were rarer than younger ones with the age structure being 192 VTs 100–299 years old, 21 trees 300–499 years old, and only three trees 500 years old or older. The average age was 163 years. Tree height, trunk girth, and crown width had normal distributions, with means of mean 32.1 m, 423 cm, 17 m, respectively. Overall, VTs were more-or-less evenly distributed across the study area, though there were biases in location when age was taken into account with older trees tending to occur at mid-elevations within the study area, but at higher elevations than other VTs. We applied a general linear model (GLM) to analyze the association between attributes of VTs and environmental data. The models revealed significant correlations between tree height and precipitation of the wettest month (p = 8.69 × 10^–4), trunk girth and mean annual temperature (p = 9.30 × 10^–4) and precipitation of the coldest quarter (p = 3.06 × 10^–4), and crown width and mean temperature of the warmest quarter (p = 8.28 × 10^–3). In conclusion, Wuzhishan City is home to diverse VTs with distributions driven at least in part by environmental factors (e.g.,temperature, precipitation, elevation, etc.). VTs can be maintained through enhanced conservation measures that acknowledge their cultural, ecological, and historical value.