Effect of Sheep Grazing on a Leafy Spurge-Infested Idaho Fescue Community

Abstract

Abstract:Leafy spurge (Euphorbia esula L.), an aggressive Eurasian forb, is invading native upland ranges dominated by bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) and Idaho fescue (Festuca idahoensis Elmer) in the Northern Rocky Mountain Province. Our objective was to determine cumulative effects of 3 summers (1992)(1993)(1994) of repeated sheep grazing on a leafy spurge infested-Idaho fescue community. Targhee ewes were systematically rotated through paddocks in small pastures. Leafy spurge stem and Idaho fescue and bluebunch wheatgrass plant densities, and frequencies of other species were determined before grazing in 1992, 1993 and 1994, and in 1995, 9 months after grazing ended. Number of viable leafy spurge seeds in seedbanks was determined in 1992 and 1995. Plant heights were measured each year. Density of leafy spurge seedlings was low in grazed and ungrazed areas in 1992 and 1994, whereas density was higher in ungrazed than grazed areas in 1993 and 1995. Grazing did not increase or decrease density of mature leafy spurge stems from 1992 to 1995. Grazing increased density of Idaho fescue but reduced density of bluebunch wheatgrass. Kentucky bluegrass, (Poa pratensis L.), Sandberg bluegrass (Poa sandbergii Vasey), annual bromegrasses (Bromus spp.), and sedge (Carex spp.) frequencies increased in grazed areas. Number of viable leafy spurge seeds in the seedbank was lower in 1995 than in 1992; this reduction was greater in grazed than ungrazed areas. Three years of repeated sheep grazing reduced numbers of leafy spurge seed in the seedbank and seedling densities, but had no effect on density of mature leafy spurge stems. There was minimal effect on the cool season native grasses, possibly because the site was grazed primarily in midsummer when these grasses are dormant. Thus, a long-term com-1 Manuscript accepted: 23 July 1997.

Reducing Euphorbia esula with a combination of sheep grazing and imazapic

“…In experiment two, sheep grazing for 1 year did not change any of the measured vegetation components. Similar to previous work (Olson and Wallander, 1998;Dahl et al, 2001), results from the two experiments indicate that sheep grazing alone will slowly alter vegetation components in a pasture infested with E. esula.…”

“…In experiment two, however, the imazapic application did reduce overall plant biomass as the grass and forb components had not developed enough to replace E. esula biomass lost after the herbicide application. Others have measured similar plant responses in E. esula infested pastures to imazapic (Markle and Lym, 2001) and to grazing (Olson and Wallander, 1998).…”

“…In the Intermountain West, the nutrient quality of E. esula is usually greater than the nutrient quality of many native grasses throughout the summer grazing season (Olson et al, 1996), which can favor sheep selection of E. esula over other plant species during late summer. Sheep or goat grazing alone will not completely remove E. esula from an infested pasture; however, the timing and intensity of sheep grazing can be managed to reduce E. esula seed productivity while having minimal impacts on desired vegetation (Lym et al, 1997;Olson and Wallander, 1998;Taylor et al, 2005).…”

Using strategically applied grazing to manage invasive alien plants in novel grasslands

“…For example, leafy spurge (Euphorbia esula) is an invasive forb that is generally avoided by cattle but eaten by sheep (Rinella and Hileman 2009). Some direct manipulation of grazing pressure has been successful in reducing the density of leafy spurge in rangelands in the USA (Lym et al 1997) but not in others (Olson and Wallander 1998;Seefeldt et al 2007). Rinella and Hileman (2009) clarified some of the inconsistencies in leafy spurge research by simulating grazing at different intensities, timing and frequencies.…”

Hierarchical Bayesian methods estimate invasive weed impacts at pertinent spatial scales

“…For example, when domestic sheep are used to control leafy spurge (Euphorbia esula L.) (Olson and Wallander 1998), no risks (e.g. overgrazing) or benefits (e.g.…”