Friday, August 7, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Alisa W. Coffin, Rocky Mountain Geographic Science Center, USGS, Fort Collins, CO
Background/Question/Methods Road networks persist in the landscape and have numerous ecological ramifications. Landscape ecologists have relied on a limited number of metrics, particularly road density and distance to road, in studies of ecological responses to roads. Transportation geographers have developed network analytic methods to characterize road networks, providing a diverse suite of metrics that describe network structure and function. This research investigated road network and landscape dynamics in north-central Florida from 1975 to 2005. Specific research questions included: How did the road network structure change over time? How did the dynamics of road network development and land cover affect patterns of landscape fragmentation? What were the differences in fragmentation patterns between forested and agricultural/open land-cover types? How did fragmentation vary across space/time as the road network changed? Road network extent, connectivity and accessibility were quantified using twenty-three indices derived from mapped features and network analysis. Network indices measured topological characteristics, providing quantitative values of network connectivity and accessibility. Changes in these metrics characterized road network development. This study explored relationships between changes in road network (linear and topological) metrics, and landscape metrics of land cover, patch size and abundance, and effective mesh size (a connectivity-based measure of fragmentation). Results/Conclusions
Overall, the road network expanded but topological connectivity decreased due to an increasing proportion of dead end roads. While accessibility of the landscape increased, topological accessibility of the road network declined. The landscape became more fragmented as effective mesh size decreased. Increased fragmentation patterns in 1975-1995 corresponded with the expansion of agricultural/open land cover and dead end roads. Fragmentation rates were greatest during 1995-2005, when there was a sharp increase in road network extent, and agricultural/open land covers were disproportionately affected by this expansion. Watershed sub-basins located along highways linking regional urban centers experienced the greatest increases in fragmentation. Decadal changes in land cover and the road network signaled a shift from agricultural expansion to suburbanization in many parts of the watershed. The results of this study challenge established ideas that road networks become more connected and accessible as regions develop. Dead end roads were an important factor in the development of this road network. Dead end roads do not affect some fragmentation metrics, so relationships between dead end roads—which in some places dominate changes in the road network—and ecological responses may go undetected. The distinct ecological effects of dead end roads and their detection merit closer scrutiny.
