Study Area
One of the unique characteristics of Maricopa County is the coexistence of relatively undisturbed natural desert and ever-increasing urban development across the landscape. As a part of the northeastern Sonoran Desert Ecoregion (Figure 1), the study area consists of the Lower Colorado Sonoran Desert positioned in the central part of the area and the Upland Sonoran Desert in the Phoenix urban outskirt. The Lower Sonoran Desert contains various kinds of vegetation such as ironwood, mesquite trees and other mixed cactus plant communities that can be less susceptible to human settlements, while the Upland Sonoran Desert is characterised by desert plants such as rich saguaro, creosote bush, palo verde, and ocotillo (Maricopa County, 2002)