Effects of human population density on the pattern of terrestrial nature reserves in China

An increasing number of studies showed that coverage of existing protected areas is not enough to protect biodiversity. However, to what extent and how human population density influence the geographical pattern of protected areas are not clear. Based on 2644 terrestrial nature reserves (NRs) in mainland China in 2015, correlation analysis showed that there was a significantly negative relationship between human density and area (R = −0.52, P < 0.001) and coverage of NRs (R = −0.21, P < 0.001), and a positive one between human density and density of NRs at county level (R = 0.64, P < 0.001) (all sample size n = 1171). These relationships could also be observed at provincial level. Counties with NRs had significantly lower human density (mean = 95 persons km⁻²) than those without (mean = 289 persons km⁻²) (P < 0.001, n = 31) across China. Both percentage of agricultural land and road density significantly and negatively correlated with area and coverage of NRs, and positively with human density and density of NRs at provincial level (all P < 0.01, n = 31). The relationships between human and NRs varied among 31 provinces, three conservation objectives of ecosystems, species and others, three hierarchical managements of national, provincial, and city-county levels, and two jurisdictional departments of forestry and non-forestry. But the general pattern of such relationships did not change. In addition, human density and density of NRs significantly positively, and area and coverage of NRs negatively correlated with density of IUCN red-list high plants and vertebrates excluding fishes at provincial level (all P < 0.05, n = 31). These results suggested that human density had substantial impacts on the geographical distribution of NRs when their sites were designated, elucidating the mechanism responsible for the low effectiveness of NRs in representing biodiversity.