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Line drawing courtesy of the US Fish and Wildlife Service. |
The demise of the beaver brought about a major alteration of the Western landscape. The beaver is an integral part of riparian ecosystems, felling trees to create reservoirs where it builds its underwater lodges, thereby trapping alluvial sediments, providing opportunities for new plant growth, and increasing the diversity of wildlife habitats. Beaver dams help control seasonal flooding, a common occurrence on many Southwestern rivers and streams, thereby preventing erosion and downcutting of riparian channels. The reservoirs formed by dams also provide wetlands for migratory birds. Eventually these dams may be abandoned, and when they slowly break away and the pools dry up, great meadows of tall grass often grow up along the floodplain. These meadows sustain large populations of deer and elk, while the remnants of felled trees provide shelter for nesting birds and smaller animals.
The wholesale destruction of the beaver in the intermountain West disrupted these ecological relationships, and as a result erosion became a serious problem while the loss of habitat led to declining ungulate and bird populations. Removal of beavers or their dams, together with livestock grazing, has contributed to arroyo cutting and gullying of the landscape. As the channel cuts deeper and the gradient increases, the water table is lowered and surface sediments begin to dry out; gradually, the vegetation becomes composed of plants tolerant of drier conditions.
References and Resources:
Chadde, S. W. and Kay, C. E. 1991. Tall willow communities on Yellowstones northern range: a test of the "natural regulation" paradigm. Pp. 231-262 In: Keiter, R. B. and Boyce, M. S., editors. The Greater Yellowstone Ecosystem. Yale University Press, New Haven.
Jones, C. G., Lawton, J. H. and Shachak, M. 1994. Organisms as ecosystem engineers. Oikos 69: 373-386.
Kay, C. E. 1994. The impact of native ungulates and beaver on riparian communities in the Intermountain West. Natural Resources and Environmental Issues 1: 23-44.
Knopf, F. L. and Scott, M. L. 1990. Altered flows and created landscapes in the Platte River headwaters, 18401990. Pp. 47-70 In: Sweeney, J. M., editor. Management of dynamic ecosystems. North-central section, The Wildlife Sociey, West Lafayette, Ind.
Martinsen, G. D., Driebe, E. M. and Whitham, T. G. 1998. Indirect interactions mediated by changing plant chemistry: beaver browsing benefits beetles. Ecology 79: 192-200.
Masslich, William J.; Brotherson, Jack D.; Cates, Rex G. 1988. Relationships of aspen (Populus tremuloides) to foraging patterns of beaver (Castor canadensis) in the Strawberry Valley of central Utah. The Great Basin Naturalist. 48(2): 250-262.
McNamee, G. 1994. Gila: The Life and Death of an American River. Orion Books, New York.
Naiman, R. J., Johnson, C. A. and Kelley, J. C. 1988. Alteration of North American streams by beaver. BioScience 38: 753-762.
Naiman, R. J., Pinay, G., Johnston, C. A. and Pastor, J. 1994. Beaver influences on the long-term biogeochemical characteristics of boreal forest drainage networks. Ecology 75: 905-921.
Stock, A. Dean. 1970. Notes on mammals of southwestern Utah. Journal of Mammalogy. 51(2): 429-433.
Stock, J. D. and Schlosser, I. J. 1991. Short-term effects of a catastrophic beaver dam collapse on a stream fish community. Environmental Biology of Fishes 31: 123-129
Zeveloff, Samuel I. 1988. Mammals of the Intermountain West. Salt Lake City, UT: University of Utah Press. 365 p.