Effects of agriculture on habitat complexity in a prairie-forest ecotone in the Southern Great Plains of North America

Abstract

Ecotones are transition zones that may be particularly sensitive to both natural and human-related disturbances to the environment. Agricultural development in the southern Great Plains of North America has resulted in marked changes in habitats and in the configurations of those habitats. Based on panchromatic National High Altitude Photography (NHAP), the effects of such development on spatial extent, relative abundance, and habitat-patch complexity for 15 land-cover types were evaluated by contrasting landscape-level habitat characteristics of a managed-native landscape (Fort Sill Military Reservation in southwestern Oklahoma, USA) with those of the adjacent landscape, where agricultural uses were the most prevalent. The managed-native landscape was predominately grassland (62.2%), with most being mixed grassland (43.4%), while the surrounding agriculture landscape was dominated by rangeland (50.7%) and cropland (13.6%). The mean area and perimeter of grassland patches in the managed-native area were greater than in the agriculture area, while values of these measures for cropland and rangeland patches were greater in the agriculture area. Mean patch shape (corrected perimeter/area) was highest for bottomland-forest, riparian, and cross-timbers habitats, reflecting the fact that these habitats typically are elongated in shape. Mean patch shapes of mesquite-savanna, bottomland-forest, and riparian patches were significantly lower in the agriculture area, a result primarily due to the straightening of edges of patches of these habitats when croplands were developed adjacent to them. With two relatively large reservoirs being present in the agriculture area, mean patch shape for water also was significantly lower than that in the managed-native landscape. Overall, fractal dimension—a measure of shape complexity of the perimeter of habitat patches—was significantly lower (based on Monte Carlo simulation) for the agriculture area than the managed-native area, mirroring the fact that habitat edges in the cropland-dominated area were less complex for many of the land-cover types. For specific land-cover types, cropland had a significantly higher fractal dimension in the agriculture area than the managed-native area, while the opposite was true for water, mixed grass, distributed areas, riparian, and bottomland forest. These results indicate that habitat complexity in the prairie-forest ecotone is reduced by agricultural development, which potentially could have deleterious effects on native plants and animals.