Characterizing the hierarchy of road network and its landscape effect with graph theory∗

Roads are conspicuous components of landscapes and play a substantial role in defining landscape pattern. Previous studies have demonstrated the link between roads and their effects on ecological processes and landscape patterns. Less understood is the relationship between landscape patterns imposed by the network in relation to road network configuration, spatial heterogeneity etc. Our hypothesis was that effect of road network on landscape patterns can be explained in relation to graph theoretical indexes describing the network features and landscape patterns. Taking Lancang River Valley in Southwest China as a case, we examined the road network features of different road grades and the landscape pattern variability at county scale. The results showed that the indexes of road network, such as corridor density, α circuitry index, β line-node ratio, and γ connectivity index, varied greatly at county scale in Lancang River valley. Road density has a positive relation with road corridor number, α connectivity index, β line-node ratio, and γ circuitry index. Patch density and average patch area (1980, 2000) have a significantly positive relationship with α , β , γ indexes which suggest landscape fragmentation was intensified with the network extension.