Zones, Biodiversity, and Degradation by Livestock
J. Boone Kauffman, Ph.D
Riparian, or streamside, areas are critical
habitat for many plants and animals in the arid West. Livestock grazing is the
leading cause of riparian degradation. Impacts to vegetation, stream hydrology,
and geomorphology can separately or synergistically affect stream functioning
and many wildlife species. Thus, riparian restoration, including the removal
of livestock, must be a high priority for the conservation of biodiversity.
J. Boone Kauffman is professor of ecosystem
sciences in the Department of Fisheries and Wildlife, Oregon State University,
Corvallis. He studies the ecology and restoration of riparian zones in the arid
West, as well as tropical forest ecology in Central and South America, and has
written more than a hundred scientific papers on natural ecosystems. He grew
up on the West Texas plains and holds a Ph.D. degree in forest ecology from
the University of California at Berkeley, as well a B.S. degree in range management
and an M.S. degree in range ecology.
Riparian zones are a unique wetland environment adjacent to rivers or streams. People have long recognized that riparian zones and rivers are the lifeblood of the western landscape, being more productive and home to more plants and animals than any other type of habitat. Scientists refer to riparian zones as hotspots of biodiversity, a characterization that is particularly apparent in arid and semiarid environments, where such zones may be the only tree-dominated ecosystems in the landscape. The presence of water, increased productivity, favorable microclimate, and periodic flood events combine to create a disproportionately higher biological diversity than that of the surrounding uplands.
|Cattle graze in a wet meadow along Blacktail Creek, Beaverhead National Forest, Montana. Streamside vegetation is cropped low, parts of the stream bank are bare, and other parts are sloughing into the creek.|
This stream in northern New Mexico has become entrenched. Over time, grazing and trampling of the soils and banks by livestock have caused the stream to widen and cut downward. Typical results of this stream degradation process include lowered water table, drier soil in the zone adjoining the waterway, and riparian-type plants (such as willows) gradually replaced by more drought-resistant plants (such as sagebrush).
At stream edges, the combination of root loss and trampling
weakens and collapses banks. Bank loss and the resulting sediment loads contribute
to downcutting, channel widening, and degradation of water quality and fish
habitats. As the channel downcuts, overbank flows cease, and subsurface water
exchange between stream and floodplain is lost. Floodplain forests evolved to
grow and develop in the environment created by large floods. By altering or
eliminating the natural flood regime, channel downcutting impedes or halts the
development of multi-layered, multi-aged--or "gallery"--forests, such
as those composed of cottonwood trees and willows, along with other riparian
plants. Loss of the riparian forests negatively affects not only the terrestrial
wildlife, but the aquatic biota as well. Loss of shade and organic inputs from
riparian vegetation results in increased stream temperature, altered water quality,
and a change in composition and abundance of the aquatic biota.
Although occupying a small portion of the landscape, riparian zones are keystone ecosystems because of their high level of biodiversity and provision of other ecosystem services. The restoration of riparian zones would yield many positive benefits, including the return of flood events to something resembling their natural patterns. Because riparian plants have adapted to survive frequent floods and other natural disturbances, they often show great resilience after the cessation of human activities that are causing degradation. Such removal of harmful activities is termed passive restoration, and in the arid West, the most significant act of passive restoration would be the removal of grazing livestock. Logically, passive restoration should be implemented first, and its effectiveness assessed, before the initiation of more active measures, such as structural modifications and reintroductions of species.
Among the greatest barriers to effective riparian recovery are political and social factors. Land and river managers have often been limited to, or limited themselves to, band-aid approaches that do not address the real causes of degradation. For example, salmon have continued to decline in the Columbia Basin of the Pacific Northwest, despite the input of billions of dollars for restoration projects and mitigating measures, because, among other reasons, livestock continue to degrade riparian zones. A prominent and popular project on public lands in the Columbia Basin has been the installation of artificial structures in smaller streams, in an attempt to re-create aquatic habitat that has been lost to decades of poor resource management. However, artificial stream structures can be expensive and often are sited and constructed poorly.
In many cases, the most effective, cheapest, and simplest approach to restoring these river courses would be to halt grazing damage and allow the streams to recover their own natural vegetative and morphological characteristics over time. But it can be extremely difficult politically for managers to make such decisions. And restoration results can take a long time to appear, whereas political demands arise much more rapidly. Yet, given the inestimable natural values that arise from healthy riparian zones, a long-term commitment to riparian restoration, preservation, and sustainable management should receive high priority. The reduction or removal of livestock from vital riparian and wetland habitats throughout the West needs to be given serious consideration by all those concerned about ecosystem health.
References available in printed version of article.