5.7.1 Landscape Pattern of Development
22.214.171.124 Potential Environmental Effects
The pattern of landscape conversion for any new infrastructure could affect terrestrial species and community diversity through at least three distinct mechanisms that also apply to algal biofuel production or other energy production (McCabe, 1994; DOE, 2009, 2010a; Garvin et al., 2011):
• Displacement of terrestrial vegetation and wildlife habitat from the facility area and replacement with a pond or photobioreactor containing a monoculture or a few species of algae.
• Reduction in local wildlife habitat area below the threshold needed for the species.
• Fragmentation of wildlife habitat such that mates are more difficult to find or mi-gration corridors are disrupted. The magnitude of land requirements (discussed in Chapter 4) and the types of conversions (discussed in section Land-Use Change in this chapter) influence the magnitude of potential effects on ecological populations and communities.
Displacement of native vegetation and individual vertebrates usually is limited to the area of the facility, but some species are sensitive to human infrastructure and tend to be displaced to distances beyond the boundaries of the facility, for example, female sage grouse avoiding nesting within 950 meters of infrastructure associated with natural gas fields (Holloran et al., 2010).
Extensive infrastructure, especially from multiple facilities, could fragment habitat for some wide-ranging vertebrates. Fragmentation of habitat is determined less by the area of a facility than by the dimensions compared to significant habitat types or corridors. One measure of fragmentation is the ratio of the perimeter (patch edge length) to the area of a habitat patch (Dale and Pearson, 1997). Thus, a linear facility would tend to be fragmenting in more environments than one that is closer to square. However, the latter configuration is more practical for system maintenance, so extensive linear facilities are not considered. Other potential measures of fragmentation include the percent of the landscape occupied by a given habitat, the number or density of habitat patches within a given area (more patches means greater fragmentation), and the degree of connectedness or isolation among habitats (McGarigal et al., 2005).
Even where habitat is not fragmented, human infrastructure and associated disturbance could reduce the habitat area beyond minimum levels required by certain species. Carlsen et al. (2004) review critical patch sizes (contiguous habitat area necessary to conserve a population) required by many species, such as the minimum patch size that can sustain a viable population. They found that few studies examined behavioral or population dynamics associated with large areas of contiguous habitat, which also contained smaller patches of unsuitable or disturbed lands (as in algal biofuel development or oil and gas development). An exception is a theoretical study of American badger at an oil production site that investigated the effects of increasing areas of patches of disturbance on an otherwise highly suitable matrix of tallgrass prairie in Oklahoma (Jager et al., 2006). Critical disturbance areas would depend on the species of concern, the habitat type, habitat suitability, and type of infrastructure.