Road-network agglomeration, road density, and protected-area fragmentation

This paper develops a new measure of the spatial pattern of roads in an area, named the Road Network Agglomeration Index (RNAI), and explores the impact of this dimension of road networks on spatial patterns of conservation networks. RNAI is more spatially descriptive than road density measures used commonly in analyses of conservation patterns, and easier to calculate than some other metrics of road network characteristics. The paper uses both RNAI and road density in a case study, performing regression analyses to explore the drivers of fragmentation of California's network of public and private conservation lands. RNAI emerges as a consistently strong indicator of the degree of fragmentation of the reserve network, complementing road density as a measure of features of road networks that affect the pattern of protected areas in a watershed. We also find that private conservation serves more often to increase rather than decrease agglomeration of the reserve network.