Chapter 4. Vegetation
97
communities sometimes extend to significantly lower elevations within narrow,
shady canyons.
Riparian ecosystems have been strongly impacted by human activities
throughout much of the arid southwest, and many riparian community types have
been greatly reduced in spatial extent and altered in composition, diversity, and
structure. In Arizona, riparian marshes, or cinegas, have become extremely rare,
likely because of the effects of ongoing stream dewatering, as well as widespread
historic channel incision, which resulted in the conversion of floodplain marshes
to riparian forests (Hendrickson and Minckley 1984, Stromberg et al. 1997a).
Other riparian vegetation types, such as Prosopis (mesquite) forests or bosques,
and Populus fremontii Salix gooddingii forests, exist only as remnants of
formerly abundant communities (Stromberg 1993a,d). These changes have
resulted from a variety of factors, including dams, groundwater pumping, live-
stock grazing, and floodplain land use. Another notable change to riparian
systems in the U.S. southwest has been the widespread establishment of Tamarix
(saltcedar), which is now abundant or dominant along many rivers in the region
(Brock 1994, Busch and Smith 1995, Everitt 1998, Shafroth et al. 2000).
Previous Page
