Kauffman, Boone, Andrea Thorpe, and Jack Brookshire. [In press 2004]. Livestock exclusion and belowground ecosystem responses in riparian meadows of eastern Oregon. Ecological Applications.
RELEVANT TO: GRASSLANDS/SHRUBLANDS
AQUATIC/RIPARIAN
LIVESTOCK
DESCRIPTION
This study examines changes in belowground processes in riparian wet (sedge-dominated) and dry (grass and forb-dominated) meadows following cessation of livestock grazing. The hypothesis was that "...soils, belowground processes, and vegetation features in riparian meadows may be influenced in ways that could affect ecosystem function and important linkages to adjacent aquatic ecosystems."
The six meadow complexes studied were in the Middle Fork of the John Day River in the Blue Mountains of northeastern Oregon, at elevations of 1066-1323 meters. Uplands were mixed conifer forests of lodgepole and ponderosa pine on south slopes, Douglas-fir, grand fir, and western larch on north slopes.
Each meadow complex contained both wet meadows dominated by Nebraska sedge (Carex nebrascensis), and dry meadows dominated by Kentucky bluegrass (Poa pratensis). Three had not been grazed, except by elk for 9-18 years; the other three were grazed by cattle. One of these was on Forest Service land, employing a deferred grazing system (grazed early in the summer one year, late summer the next); the other two were private lands grazed season-long each year.
The study measured infiltration rates, belowground biomass, and soil properties (bulk density, porosity, soil organic matter, ad potential net N mineralization).
MAJOR FINDINGS
- Total aboveground biomass: ungrazed dry meadows contained 69% more total aboveground biomass; ungrazed wet meadows 49% more than grazed wet meadows.
- Total belowground biomass: Dry ungrazed meadows had 50% greater in belowground biomass; wet ungrazed meadows had 62% greater. The top ten cm contained most of the belowground biomass. "Our estimates of root biomass are similar to those few studies that measured root biomass in similar riparian plant communities [I.e., Yellowstone National Park, northeastern Oregon, Nevada
- Soil bulk density: 16% lower in ungrazed dry meadows; 32% lower in ungrazed wet meadows.
- Soil pore space (i.e., water storage capacity): 6% more in ungrazed dry meadows; 12% more in ungrazed wet meadows. "These differences in soil bulk density and soil pore space suggested a greater degree of recovery from livestock compaction in exclosed wet meadows than dry meadows."
- Rate of net potential nitrification and mineralization: 149-fold and 32-fold greater in ungrazed compared to grazed wet meadows;
- Concentrations of mineral forms of N: low at all sites.
- Infiltration rates: 11-fold greater in ungrazed dry meadows; 3-fold grater in ungrazed wet meadows. "This indicates that recovery of soil properties can be quite dramatic even following over a century of heavy livestock grazing."
This study indicates that the surface 10 cm of a single hectare of ungrazed dry meadow would contain 61,000 L more water than a hectare of grazed dry meadow; and 121,000 more liters in the surface 10 cm of one hectare of ungrazed wet meadow compared to grazed wet meadow.
Based upon a GIS analysis of aerial photos of the 30-km riparian zone sampled in this study (145 hectares of dry meadows and 64 hectares of wet meadows), "Our results suggest that if the entire area was excluded from livestock, the surface 10 cm of soil in the meadows alone (about 60% of the riparian zone cover) could potentially store 16.6 million L more of water than if the area were grazed by cattle. And, this estimate does not include the entire soil profile."
The authors conclude, "Livestock removal was found to be an effective approach to ecological restoration resulting in significant changes in soil, hydrological, ad vegetation properties that at landscape scales would likely affect stream channel structure, water quality and the aquatic biota."
QUESTIONS RAISED FOR THE THREE FORESTS
- Is there any evidence that the findings in this and related studies (cited in the article) would not hold for wet and dry riparian meadows in the Three Forests? The implications of livestock grazing in riparian meadows include loss of water storage; loss of bank-stabilizing root mass; and potentially higher stream water temperature.
- Have the Three Forests ever estimated the loss of water storage in their wet and dry meadows due to livestock grazing?
RELEVANCE TO FOREST MANAGEMENT
- Evidence of global warming and continued drought in the southern Utah region requires re-evaluation of human activities that exacerbate drought conditions, specifically livestock grazing. The EIS must discuss these implications unless the Forests have evidence to the contrary.
- Livestock should not graze in riparian areas.
- There is a need for large livestock-free areas on each of the Three Forests, given the cumulative impacts of drought, invasive species, staff and budget inability to track whether particular endemic, sensitive or other native plants are declining due to selective grazing, soil compaction, riparian destabilization, and competition with wildlife.