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In southwestern North America, riparian habitats have declined precipitously in the last century both within and outside protected areas such as national parks,U.S. Fish and Wildlife Service refuges, and Bureau of Land Management and biosphere reserve lands. These declines are primarily due to anthropogenic perturbations such as alterations in river flow regimes, agricultural conversion, livestock grazing, and urban expansion (Webb et al. 2003). In the southwestern United States and northwestern Mexico the decline of riparian habitat and loss of native cottonwood (Populus fremontii), willow (Salix gooddingii) gallery forests, and adjacent mesquite (Prosopis sp.) bosques has been accompanied by the invasion of nonnative tamarisk (Tamarisk sp.), or salt cedar. This change has resulted in a dramatic shift towards the dominance of tamarisk in riparian vegetation communities within most protected areas (Shafroth et al. 2005). The reduction and shift in vegetation composition within riparian habitats in western North America has resulted in their classification as globally imperiled by The Nature Conservancy (Comer at al. 2003), and has had a tremendous impact on neotropical migrant birds. Although riparian habitat comprises less than one percent of the landscape in southwestern North America, it supports more breeding bird species than all other western habitat types combined (Anderson and Ohmart 1977). Riparian areas serve as critical breeding, winter, and stop-over habitat for birds, supporting 10 times greater bird numbers than surrounding uplands (Anderson et al. 2004). In fact, most wildlife within xeric environments of protected areas in Mexico and the United States depend on resources (e.g., water, cover, food) provided by riparian habitats during some time of their annual cycle (Rosenberg et al. 1991).