Impacts of Natural Environmental Factors and Anthropogenic Activities on the Distribution of Threatened Orchid Species in China

Natural environmental factors and anthropogenic activities could have strong impacts on threatened species distribution. Based on Random Forest modeling and ordinary least squares models, we tested the correlations between natural environmental factors (mean annual temperature (MAT), mean annual precipitation (MAP) and elevation range), anthropogenic activities (changes in cropland area, population density and pasture area) over different periods (between 1700 and 1800, between 1800 and 1900, and between 1900 and 2000) and ratio of threatened orchids in China. The results showed that threatened orchids were concentrated in Southwest China, Central China and Northeast China. The ratio of threatened orchids was positively correlated with MAT and MAP, but negatively correlated with elevation range. In addition, the three anthropogenic activity variables most correlated with threatened orchids ratio were changes of cropland area between 1900 and 2000, population density between 1700 and 1800, and between 1800 and 1900. These correlations were positive, indicating that areas with more anthropogenic activities had more threatened orchids. Moreover, MAP and changes of cropland area between 1900 and 2000 together were more correlated with threatened orchids ratio than other variables. These findings suggest important roles of contemporary climate and anthropogenic activities in shaping the distribution of threatened orchid species in China.