Old ginkgo trees in China：Distribution, determinants and implications for conservation

Abstract

China has a long history of planting ginkgo trees, and there are many large old ginkgo trees in rural and urban areas of China. Those large old ginkgo trees have aesthetic and cultural values and play an important role in regulating landscape and ecological functions. However, the geographical distribution and its determinants of large old ginkgo trees in China are still unexplored. In this study, we first collected from published references the county-level distribution data of ginkgo trees older than 100-year in China. Then we used generalized linear regression and random forest models to analyze the influence of 18 variables representing macroclimate, topography, soil conditions, and intensity of human activity on the occurrence and density of old ginkgo trees. We found that 66,184 old ginkgo trees were distributed in 818 counties of 23 provinces with the county-level average density of 0.11 ± 0.04 trees per km2. Old ginkgo trees were mainly distributed east of the Hu Huanyong line where the climate is humid and human population density is high. The probability of occurrence of old ginkgo trees was predominately affected by macroclimate and soil conditions. It significantly decreased with increasing proportion of soil sand content, soil pH, and climate stability, and significantly increased with increasing temperature and precipitation. In contrast, the density of old ginkgo trees was predominately affected by human activity, significantly increasing with human activity intensity (i.e., human population density, gross domestic product, and night-time light intensity). In conclusion, the occurrences of old ginkgo tree were constrained by macroclimate and soil conditions, while their density was mainly driven by human activity.