Belsky, AJ, A Matzke, and S Uselman. 1999. Survey of livestock influences on stream and riparian ecosystems in the western United States. Journal of Soil and Water Conservation 54:419-431.
| RELEVANT TO: | AQUATIC/RIPARIAN |
| WILDLIFE | |
| LIVESTOCK GRAZING | |
| WATERSHED HEALTH |
DESCRIPTION
This is a review of 143 scientific documents regarding the influences of livestock on western stream and riparian ecosystems. Highest priority in Belsky et al.’s literature survey was given to:
1st: Recent papers in refereed journal presenting experimental manipulations
2nd: Descriptive or comparative studies of grazed vs. naturally or historically protected areas where similarly of initial conditions could be inferred
3rd: When there was a paucity of data, non-peer-reviewed reports, usually from government documents or symposia.
“In no case were general conclusions drawn from unrefereed reports or from studies showing anomalous results. Instead, all conclusions were based on what seemed to be the consensus of experts in the field” (p. 425).
Environmental impacts were defined as environmental changes that were significant at the P <0.1 level.
MAJOR FINDINGS
The text of the article summarizes and documents the following influences of livestock on riparian areas:
- Impacts that occur at the local level
- Water quality
- Increased nutrient concentrations
- Increased bacteria/protozoa
- Increased sediment load and turbidity
- Increased water temperature
- Stream channel morphology
- Increased channel depth
- Increased channel width
- Decreased channel stability during floods
- Decreased water depth (except during peak flow)
- Channel bed
- Gravel lost in erosional environment
- Fine sediments increased in depositional environment
- Reduced streambank stability
- Laid back streambank angle
- Reduction in quality and quantity of streambank undercuts
- Fewer meanders and unvegetated gravel bars
- Decrease in number and quality of pools
- Hydrology (stream flow patterns) [Note: beaver have the opposite effect on all of the following:]
- Increased overland flow (runoff)
- Increased peak flow
- Increased flood water velocity
- Decreased summer and late-season flows
- Lowered water table
- Riparian zone soils
- Increased bare ground
- Increased erosion (water, ice, and wind)
- Decreased litter layer
- Increased compaction
- Decreased infiltration
- Declines in soil fertility (e.g., less soil organic matter, loss of top soil)
- Instream vegetation
- Increased algae
- Often a decline in abundance of higher plants (submerged and emergent)
- Streambank vegetation
- Decline in herbaceous cover, biomass, productivity, and native diversity
- Decline in overhanging vegetation
- Decline in tree and shrub biomass and cover
- Altered species composition
- Simplified structure (vertical and horizontal)
- Plant age-structure becomes even-aged
- Altered plant phenology
- Impeded plant succession
- Aquatic and riparian wildlife
- Fish
- Decrease in species diversity, abundance, and productivity
- Reduction in use of preferred habitats
- Invertebrates
- Altered diversity, abundance, and species composition
- Amphibians and reptiles
- Decline in diversity, abundance and species composition
- Birds
- Altered diversity, abundance and species composition
- Mammals (large and small)
- Altered (sometimes but not always) diversity, abundance, and species composition
- Threatened and endangered species
- Reduced abundance
- Landscape and regional consequences
- Downstream waters have higher temperatures and sediment loads
- Downstream flood levels are higher
- Quantity of water to downstream ecosystems is lower during low-flow periods
- Forested connectors and wildlife migratory routes between high and low elevation ranges are lost
- The diversity and abundance of migratory birds and wildlife are reduced
- Habitat mosaic is homogenized
- Corridors for migration of salmonids and other species are fragmented
- Areas set aside for human recreation are reduced in quality
- Commercial and recreational fishing opportunities are reduced
- Domestic water supplies require more filtration and treatment by water-treatment plants, leading to higher utility rates
- More sediment is deposited in lakes and reservoirs, thus reducing reservoir life and hydroelectric capacity
- Sediments in water damage hydroelectric turbines
- Higher sediment loads increase maintenance costs of irrigation canals
QUESTIONS THIS DOCUMENT RAISES FOR SOUTHERN UTAH’S THREE NATIONAL FORESTS
- Have any of the Three Forests ever surveyed their Forest for (a) beaver and (b) potentially suitable beaver habitat?
- Have any of the Three Forests ever analyzed the potential ecological, hydrological, and socioeconomic benefits of restored beaver populations on the Forest?
- Have any of the Forests analyzed impacts of riparian livestock grazing on beaver?
RELEVANCE TO FOREST MANAGEMENT
The restoration of beaver and their water engineering on the three southern Utah national forests are crucial to long-term watershed health in light of global warming and predicted drying of the Colorado Plateau during the next two decades. The following are excerpts from two articles our coalition has earlier submitted to each of the three Forests:
- Scientists and managers need to look at climate change as a current, not just a future, threat to species. Global warming makes the water engineering by beaver crucial to long-term watershed health on southern Utah forests.
McCarty, John P. 2001. “Ecological Consequences of Recent Climate Change.” Conservation Biology Vol.15, No. 2: 320-331
- “Recent trends in Colorado Plateau precipitation and the PDO [Pacific Decadal Oscillation] suggest that climate of the region may become drier for the next 2-3 decades in a pattern that could resemble the drought of 1942-1977… Water resources were heavily affected during the early part of the 1942-1977 drought [citation]; the population of the region has increased fourfold since the mid-1950s, substantially increasing the demand for water in a region without abundant supplies and creating the possibility of severe or catastrophic consequences if such a drought were repeated.”
U.S. Geological Survey. 2002. Precipitation history of the Colorado Plateau Region, 1900-2000. USGS Fact Sheet 119-02