VEGETATION AND SOIL RESPONSES TO GRAZING SIMULATION ON RIPARIAN MEADOWS

Riparian areas have not responded consistently to grazing systems, sug gesting that more knowledge is needed to explain how different areas r espond to specific stresses. Several studies were conducted to determi ne herbaceous plant response to simulated grazing on riparian areas. O ne low-elevation redtop (Agrostis stolonifera L.) site in Oregon and 2 high-elevation sedge (Carex spp. L.) sites in Idaho were studied for 3 years. Several combinations of defoliation, compaction, nutrient ret urn, and season of use were examined. The redtop community responded t o spring, fall, or spring-fall defoliations by maintaining or increasi ng the following year's aboveground biomass production. The sedge comm unities maintained or decreased the following years's biomass producti on after spring, mid summer, or late summer defoliations. An increase in forbs occurred in 1 sedge community following spring defoliations t o 1- or 5-cm residual stubble heights. The most consistent plant respo nse among areas was reduction in height growth and biomass production following compaction treatments. When both defoliation and compaction are considered, it appears that spring, fall, or spring and fall grazi ng to a 5-cm stubble height on the redtop site would not decrease ripa rian herbage production. In contrast, when defoliation, compaction, an d nutrient return effects are considered in the mountain meadow sedge- dominated communities, grazing once annually during the growing season to a 5-cm stubble height in the spring, or to a 10-cm stubble height in late summer, or at a utilization rate exceeding 30% of the total an nual biomass production can reduce herbage production significantly. R esults suggest that many of the land management agency riparian guidel ines would maintain biomass productivity in these sedge-dominated comm unities.