Road network development and landscape dynamics in the Santa Fe River Watershed, north-central Florida, 1975 to 2005.

摘要

Roads are known to have numerous ecological effects. It is postulated that networks of roads have cumulative ecological effects that are unaccounted for in the analysis of single road effects. Common ways researchers account for road networks include the calculation of road density or distance-to-road metrics. Transportation network analysis provides an alternative, quantitative measure of road networks that also provides information about the structure and function of the road network. Road networks in the Santa Fe River Watershed of north central Florida were studied using network analysis to understand how the network has changed from 1975 to 2005. This investigation was coupled with a parallel analysis of landscape fragmentation in the same region. As low-order rural roads were added to the network, the network expanded but the overall network connectivity decreased. While accessibility of the landscape increased over time, accessibility of the road network declined. The landscape became more fragmented as effective mesh size, a connectivity-based measure of fragmentation, decreased over time. Fragmentation rates were greater during the final decade of the study, 1995--2005, corresponding to a dramatic increase in road network extent. The changes in the watershed signal a shift from agricultural expansion, predominant in 1975--1985, to suburbanization. Watershed sub-basins located along highways linking regional urban centers experienced the greatest increases in fragmentation. The addition of dead-end roads was an important change in the road network structure, particularly during the second decade (1985--1995). This class of roads has specific characteristics and potential ecological effects which may not be fully accounted for in the effective mesh size metric. The use of network analysis can provide additional information about how roads fragment landscapes and the dynamics of landscape change caused by road networks.