Riparian forests, which support rich biological diversity in the North American southwest,
have experienced a sharp decline in the last century. The extent of this decline has been estimated
to range from 70% to 95% across the southwest (Johnson and Haight, 1984). The principal
components of riparian forests which sustain a broad spectrum of species and describe the overall
health of a system are cottonwoods (sp. Populus) and willows (sp. Salix). The importance of
cottonwoods is aptly described by Rood et al (1993):
"....these trees provide the foundation of the riparian forest ecosystem in semi -arid
areas of western North America. Unlike wetter areas to the east and west, a loss of
cottonwoods in these riparian areas is not compensated through enrichment from
other tree species. If the cottonwoods die, the entire forest ecosystem collapses."
Cottonwood and willow species are adversely affected by anthropogenic influences ranging most
prominently from the introduction of regulated flows via dams to agricultural clearing, water
diversions, livestock grazing, and domestic settlement. These influences effectively alter the system
hydrology that the forests rely upon.
As the widespread destruction of these forests and the associated irreparable damage to
endangered species habitat has come into clear view in the past decade, research efforts have focused
upon identifying the ecological needs of riparian systems. The potential of modifying such systems
to soften the human impact upon them, in effect presenting further alterations on a hydrologic system
to return it to its natural regime, is another component of the research on riparian systems.
The Bill Williams River riparian corridor, near Parker, Arizona (Figure 1.1), contains the last extensive native riparian habitat along the lower Colorado River (BWC Technical Committee, 1993).
This unique resource was established as the Bill Williams River Management Unit, Havasu National
Wildlife Refuge in 1941 and covers 6105 acres along the lower 12 miles of the Bill Williams River
(Rivers West, 1990). The Bill Williams Unit is currently managed by the U.S. Fish and Wildlife
Service of the U.S. Department of Interior. The U.S. Fish and Wildlife Service also funded this
research effort.
The lush vegetation corresponding to the wetland conditions along the valley floor
sharply contrast with the Sonoran desert landscape of the upper valley walls creating a magnificent
picture. The Management Unit terminates at Lake Havasu, which forms the confluence of the Bill
Williams and Colorado Rivers. The system provides habitat for a wide variety of species, many of
which are endangered or state- listed species, including habitat for neotropical migratory birds. This
habitat has undergone serious degeneration during the past quarter century. The recruitment of
cottonwood and willow trees has been fatally interrupted by anthropogenic encroachment in the form
of the construction of Alamo Dam in 1969 at the head of the Bill Williams River and commercial
development along the River.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/614210 |
| Date | January 1993 |
| Creators | Harshman, Celina Anne, Maddock, Thomas III |
| Contributors | Department of Hydrology & Water Resources, The University of Arizona |
| Publisher | Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ) |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Technical Report |
| Source | Provided by the Department of Hydrology and Water Resources. |
| Rights | Copyright © Arizona Board of Regents |
| Relation | Technical Reports on Hydrology and Water Resources, No. 93-040 |
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