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4 / Riparian Ecosystem Recovery who do not have a background in natural resources - including students, educators, developers, public officials, and landowners - can readily use it as well. Because this book is based for the most part on an evaluation of riparian revegetation efforts in Arizona (Briggs 1992), a principal focus is on evaluat- ing the damaged riparian site to determine the potential effectiveness of re- vegetation. However, other types of recovery strategies (e.g., improved live- stock grazing, in-stream modifications) are discussed as well. Although most of the lessons presented here have been learned from experiences in arid wild- land areas, many of the strategies are also relevant to nonarid climates and urban areas. Background on Riparian Ecosystems Riparian ecosystems are characterized by high diversity in both plant and wildlife species. The mesic nature of riparian areas permits the establishment and growth of many plant species not found on adjacent, more xeric uplands (Warren and Anderson 1985). Youngblood et al. (1985) found more than 600 plant species within 469 fifty-square-meter sample plots in eastern Idaho and western Wyoming. Spear and Mullins (1987) observed that waterfowl, winter- ing bald eagles (Haleaeetus leucocephalus), peregrine falcons (Falco pere- grinus), and whooping cranes (Crus americana) are constant visitors to the riparian ecosystem along the Rio Grande River in New Mexico. In addition, riparian ecosystems are home to many species of amphibians and reptiles. Mammals such as desert shrews (Notiosorex crawfordi), hoary bats (Lasiurus cinereus), mice (Peromyscus spp.), bobcats (Felis rufus), and mule deer (Odo- coileus hemionus) also are very much a part of these ecosystems. Hubbard (1977) described riparian areas as having a fairly high endemism including a relatively large number of endangered species. Riparian ecosystems in arid parts of the world differ in many respects from those in more humid climates. One of the more obvious differences is the abrupt transition between the mesic riparian zone and surrounding arid areas. In the Sonoran Desert, for example, it is common to find riparian areas where you can reach out and touch a phreatophytic species such as a Fremont cotton- wood tree (Populus fremontii) with one hand and a xerophytic species such as a saguaro cactus (Carnegiea gigantea) with the other. Riparian ecosystems take on many forms and are characterized by a variety of plant communities. Riparian ecosystems can be narrow, with abrupt transi- tions between the riparian and upland plant communities, or broad, with the