|Riegel, Greg - USDA-FOREST SVC|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2005
Publication Date: May 1, 2006
Citation: Blank, R.R., Svejcar, A.J., Riegel, G. 2006. Effect of grazing exclusion on soil attributes in a sierra nevada riparian meadow. Rangeland Ecology and Management. 59:321-329. Interpretive Summary: There has been considerable controversy about the effects of cattle grazing on riparian and meadow ecosystems. We studied the effects of grazing on soil characteristics in a Sierra Nevada riparian meadow in northern California. We found there were few consistent effects of grazing on soil chemistry or rooting characteristics of the meadow plants. Most of the measured differences between grazed and non-grazed treatments occurred at the forest-meadow boundary, rather than at the meadow/stream edge or at the mid-meadow location. In general there was a steep moisture gradient across the meadow (from the forest edge to the stream), which had much more influence on soil characteristics than did grazing.
Technical Abstract: Few studies in native riparian systems have evaluated the impact of grazing on soil nutrient availability. We measured the effect of livestock grazing on soil attributes, emphasizing soil-solution chemistry, in a Sierra Nevada riparian meadow. Treatments were livestock exclusion and grazing to leave 1000 kg/ha of vegetation. Ceramic tension lysimeters were placed in the treatments (two replicates) by landscape position (stream edge, mid-floodplain, and forest edge), and by depth (approximately 0.1, 0.6, and 1.2 m below the soil surface). Lysimeter water was extracted twice monthly in April, May, and June of 1990 through 1993 and cations and anions were quantified. In addition, KCI-extractable nitrate and ammonium, bicarbonate-extractable ortho-P, DTPA-extractable Mn, Cu, Fe, and Zn, and root length density were quantified in soils by treatment, landscape position, and soil depth in July of 1991 and Sept. Of 1993. Significant (P<0.04) treatment effects were largely limited to the forest edge position; the grazed treatment had greater lysimeter-extractable Na, Ca, Mg, and nitrate, higher pH, and less K and ammonium than the excluded treatment. Compared to the corresponding excluded treatment: in 1991, bicarbonate-extractable P was significantly greater on the grazed forest edge position and DTPA-extractable Mn was significantly greater at the grazed stream edge position; in 1993, extractable nitrate was significantly higher in the 0-25 cm depth increment of the grazed treatment and DTPA-extractable Zn was significantly greater on the grazed mid-floodplain position. Grazing did not result in more reduced soil conditions relative to the excluded treatment. Root length density (RLD) was not affected by grazing. Grazing effects were most pronounced at the forest edge position possibly due to spatial transfer of nutrients via cow urine and feces. Assessment of riparian soil chemistry must account for the steep moisture (and thus redox) gradient common in riparian ecosystems.