Impacts of road networks on the geography of floristic collections in China.

Biological collections are critical for the understanding of species distributions and for formulating biodiversity conservation strategies. However, biological collections are susceptible to various biases, including the "road-map effect", meaning that the geography of biological collections can be influenced by road networks. Here, using species occurrence records derived from 921,233 plant specimens, we quantified the intensity of the "road-map effect" on floristic collections of China, and investigated its relationships with various environmental and socio-economic variables. Species occurrence records mainly distributed in major mountain ranges, while lowlands were underrepresented. The distance of species occurrence records to the nearest road decreased from 19.54 km in 1960s to 3.58 km in 2010s. These records showed significant clustering within 5 km and 10 km buffer zones of roads. The road density surrounding these records was significantly higher than that in random patterns. Collectively, our results confirmed a significant "road-map effect" in the floristic collections of China, and this effect has substantially intensified from the 1960s to the 2010s, even after controlling for the impact of road network expansion. Topographic, climatic and socio-economic variables that determine regional species diversity, vegetation cover and human impact on vegetation played crucial roles in predicting the intensity of the "road-map effect". Our findings indicate that biological surveys have become increasingly dependent on road networks, a trend rarely reported in published studies. Future floristic surveys in China should prioritize the lowland areas that have experienced stronger human disturbances, as well as remote areas that may harbor more unique and rare species.