Effects of road features on the phytogeographical characteristics of plant species on natural-area roadsides

Road features can affect the species distribution along road verges; however, we do not know much about their significance. This research was intended to assess the importance of some road features including age, traffic, width and side slope in determining the species composition and chorotype distribution along natural area roadsides. Sampling was performed by a stratified random method, so 38 sites by twelve asphalt roads were sampled within 100-m2 plots. Canonical correspondence and redundancy analyses were conducted to describe the correlation of road features and elevation with species distribution and chorotypes along roadsides. The results showed that the road age and traffic volume were the important road features determining chorotype composition along the rangeland roadsides. Although elevation explained some variation in chorotype data, it had a lower effect than the road age. However, elevation was the most important variable in species distribution along the roadside habitats. Road age, road width, traffic volume and roadside slope were the other important variables in species distribution along the natural-area roadsides. The response curve of chorotypes to the road age and traffic volume showed that medium-aged roads and medium traffic volume provided optimum conditions for the native uni-regional chorotype. Medium-aged roads also provided optimum conditions for some bi-regional and pluriregional chorotypes. In conclusion, road features such as age and traffic volume play an independent and more important role in chorotype distribution along the natural area roadsides, compared to elevation.