Rural land use bifurcation in the urban-rural gradient

The classic urban-rural gradient concept assumes a decline in land use intensity from an intensively developed urban core outward to residential suburbs, culminating in lightly developed rural areas. The concept provides a common framework directing urban socio-ecological research. Given that rural land use includes woodlands and croplands, and croplands appear as ecologically depauperate as urban lands, we investigated land-use patterns along urban-rural gradients for 30 large metropolitan areas in the eastern United States. We predicted a bifurcation at the rural end of the gradient between woodland and cropland land use that does not correspond with human population density (expected to be relatively low in rural areas regardless of land use type). Our data indicated that 'rural' was a poor substitute for 'natural' as the rural end of the gradients bifurcated at the rural end between woodland and cropland - croplands being demonstratively poor ecological habitats. Indeed, we found that when defined by habitat quality, the habitat known to be biotically homogenized (urban and cropland) remained steady along the urban-rural gradient. Our results do not undermine the utility of the urban-rural gradient framework, but do suggest that the gradient and/or human population density do not necessarily indicate shifts in habitat quality.