by Evan H. Girvetza, James H. Thorneb, Alison M. Berrya, Jochen A.G. Jaegera
Landscape fragmentation due to urban development, transportation infrastructure, and agriculture poses a threat to environmental integrity. There is a need to quantify the level of landscape fragmentation in an ecologically meaningful way for inclusion in planning and decision-making. Effective mesh size (meff) is an ecologically relevant metric that quantifies landscape fragmentation based on the probability that two randomly chosen points in a region are located in the same non-fragmented patch.We investigated variation in meff measured by transportation districts, municipal counties, and six spatial levels of watersheds within the state of California. Four fragmentation geometries were developed by overlaying highways, roads, urbanized areas, agricultural areas, and natural fragmenting features. Twomeff calculation methods were compared: one where planning unit boundaries fragment the landscape (CUT), the other allowing for cross-boundary connections (CBC). The CUT procedure always produced lower meff values than CBC, with greater differences occurring in smaller planning units, confirming the bias introduced using boundaries with landscape metrics. Calculatedmeff values varied from0 to 20 885km2 across 6994 units in California. Roads contributed the most to fragmentation, while agriculture contributed little, as California’s agricultural areas are already heavily fragmented by roads. This paper provides a systematic, quantitative, and intuitive method for transportation, land use and environmental planners to analyze cumulative impacts of multiple fragmenting features across a range of spatial scales within a variety of planning units. This approach could be used for analyzing the impact of future land development scenarios, and integrated into regional planning processes.
related articles about the Californian cities: