Diversity and density patterns of large old trees in China

Abstract

Large old trees are keystone ecological structures that provide vital ecosystem services to humans. However, there are few large-scale empirical studies on patterns of diversity and density of large old trees in human-dominated landscapes. We present the results of the first nationwide study in China to investigate the patterns of diversity and density of large old trees in human-dominated landscapes. We collated data on 682,730 large trees ≥ 100 years old from 198 Chinese regions to quantify tree species diversity, tree density and maximum tree age patterns. We modelled the effects of natural environmental variables (e.g. climate and topography) and anthropogenic variables (e.g. human population density and city age) on these measures. We found a low density of large old trees across study regions (0.36 trees /km 2), and large variation in species richness among regions (ranging from 1 to 232 species). More than 95% of trees were < 500 years old. The best fit models showed that: (1) Species diversity (species richness adjusted by region size) was positively associated with mean annual rainfall and city age; (2) Density of clustered trees, which are mostly remnants of ancient woods, was negatively influenced by human population density and rural population (% of total population). In contrast, the density of scattered trees, which are mostly managed by local people, was positively correlated with mean annual rainfall and human population density. To better protect large old trees in cities and other highly-populated areas, conservation policy should protect ancient wood remnants, mitigate the effects environmental change (e.g. habitat fragmentation), minimize the negative effects of human activities (e.g. logging), and mobilize citizens to participate in conservation activities (e.g. watering trees during droughts).

On the Management of Large-Diameter Trees in China’s Forests

“…China has a large number of large-diameter tree species. More than 700 species can grow to be large and older than 100 years in human-dominated landscapes [35,36]. Ancient Ginkgo biloba L., Ficus religiosa L., Cinnamomum camphor L., and many tropical tree species have extremely large diameters that DBH > 60 cm.…”

“…Yet some of them are fragmented and are disappearing [53,54]. Given that large-diameter trees in natural forests are vulnerable to habitat loss and fragmentation [29], atmospheric drought and other anthropogenic disturbances [35], the fate of large-diameter trees in these forests still hangs in the balance. Large-diameter trees are occasionally found in secondary forest (Figure 1b).…”

“…The situation is even worse in human-dominated landscapes. For example, a recent study found about 682,730 large-diameter trees ≥ 100 years old from 198 city-level regions of China, with only 0.36 trees per km 2 at the national level [35]. The density of large-diameter tree varies substantially from 0.002 trees/km 2 (Tongyu County) to 24.18 trees/km 2 (Macao).…”

“…Large-diameter trees in human-dominated regions are known for their high cultural and socioeconomical values [1,13,35]. For example, large Ginkgo biloba and Ficus religiosa trees are regarded as sacred symbols that have important spiritual value to Chinese people [40] and followers of Buddhism [13].…”

“…For example, 149,652 trees were transplanted to Guangzhou City in 1990-1994, resulting in a huge loss of large-diameter tree resources in natural forests [61]. Moreover, large-diameter trees transplanted to human dominated landscapes die rapidly due to insufficient management, unsuitable habitat, and those which survive transplanting are vulnerable to climate warming, severe drought and air pollution [35,62]. This calls for urgent action on the sustainable management of large-diameter trees in human-dominated landscapes.…”