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Effects of Land Use Changes

Primary Question (chapter 3): What are the likely effects of expanding human populations, urbanization, and infrastructure development on wildlife and their habitats?

Related Question (chapter 6): How have land uses changed in the South, and how might changes in the future affect the area of forests?

The use and configuration of forest land can influence the suitability of forests as habitats for wildlife species. However, at this time, there are no regional-level models for explicitly forecasting the effects of land use changes on wildlife. To address how land use could affect terrestrial ecosystems, we surveyed the body of research on the effects of various land uses and management on terrestrial animal species and found:

• Urban land uses have important impacts on bird populations. Urbanization restructures forest habitat by decreasing forest area and patch size while increasing edge relative to interior forest habitats (see chapter 1). As a result, avian species composition is altered, nest predation increases, and habitats become isolated. Often bird diversity remains high, but there is a shift in species represented. For example, urbanization generally leads to declining populations of forest insectivores, neotropical migrants, and forest interior specialists (chapter 3).

• While the greatest impacts of urbanization seem to be related to habitat fragmentation and loss, increased human presence also has indirect effects. Evidence suggests that the presence of houses adjoining forest tracts can reduce the habitat value of those tracts for sensitive neotropical migrant birds.

• Urban environments support fewer species of mammals than rural areas and tend to support habitat generalists rather than specialists. Highly urbanized settings support large populations of exotic species such as the house mouse and Norway rat. With green spaces in the urban area, many more species, especially small species, may persist. Mammalian predators such as bobcats and gray fox are generally excluded from habitat in highly developed areas. Urbanization also tends to exclude specialized species of reptiles, amphibians, and invertebrates while generalists can persist in even highly urbanized areas. Fragmentation can isolate otherwise suitable habitats. Examples of urban-sensitive species include the gopher tortoise and the timber rattlesnake in east Texas.

• As urbanization reduces and fragments some forest areas, the remaining large forest tracts on public and private lands may increasingly contribute to the conservation of many sensitive wildlife species. Given the importance of landscape structure in determining the suitability of habitats in urban and agricultural areas (chapter 3), maintaining habitat connectivity can enhance ecosystem function in these areas.

• Red imported fire ants have a substantial impact across an increasing range in the South. While most abundant in open habitats, they invade forests from along the margins created by roads and power lines. These ants displace and/or prey on native arthropods, reptiles, amphibians, and rodents, disrupting food webs and restructuring forested ecosystems (chapter 3).

• Several other exotic animals, such as feral pigs, cats, dogs, and exotic birds influence wildlife through predation, displacement of native species (especially birds), and habitat destruction (especially pigs). Localized impacts may be severe. For example, impacts of feral pigs have become very serious in rare wetlands in the Ozark-Ouachita Highlands. Population growth and expanding wildland-urban interfaces will result in growing problems with feral domestic animals (chapter 3).

• Agricultural land is often interspersed with woodlots and other forest habitat. Habitat connectivity, which is often provided by vegetated fencerows, greatly influences the presence of birds and other species in agricultural areas. Isolated forest habitats can serve as ecological traps for some species by focusing populations in small areas along with a high concentration of nest predators (chapter 3).

• Many bird species that depend on open habitats such as grasslands, prairies, savannas, glades, and barrens are now in serious decline in the Eastern United States. Declines are partially explained by the conversion of pastureland to cultivated row crops, the switch to “clean pastures” dominated by exotic cool-season grasses, and by the loss of fencerows as new agricultural technologies favor bigger fields.

• Forecasts of land use change and measures of forest fragmentation suggest that bird species may be subjected to the most change in the Piedmont subregion (chapter 1 and chapter 6). Accordingly, we anticipate declines of neotropical migrants and forest interior specialists in these areas. Implications for neotropical migrants may be especially important, since this group of birds is experiencing global decline.