|Estell, Richard - Rick|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2010
Publication Date: 5/15/2010
Publication URL: http://handle.nal.usda.gov/10113/58280
Citation: Utsumi, S.A., Cibils, A.F., Estell, R.E., Baker, T.T., Walker, J.W. 2010. One-seed juniper sapling use by goats in relation to stocking density and mixed grazing with sheep. Rangeland Ecology and Management. 63:373-386. Interpretive Summary: Encroachment of shrubs such as one-seed juniper into rangelands is a serious problem for livestock producers. A study was conducted to determine if small ruminants could be used in targeted grazing strategies to suppress sapling growth of junipers. Because domestic livestock typically avoid feeding on juniper, this study examined approaches to increase shrub browsing intensity to levels that would damage sapling growth without permanently affecting the grass understory. Goats and mixed species (goats plus sheep) were examined during summer and spring at two stocking densities. Animals tended to remove needles and small stems from small saplings, while debarking was the main impact on taller plants. High density stocking by goats led to increased feeding time on juniper saplings compared to goats in low density stocking. Mixed species high-density stocking resulted in the highest proportion of small saplings exhibiting high defoliation. Herbaceous vegetation use was greater with mixed-species that with goats alone, and greater with low density than high density stocking. Both stocking density and mixed-species grazing can be used to alter feeding behaviors that increase utilization of juniper saplings by goats.
Technical Abstract: To successfully suppress reinvasion of one-seed juniper (Juniper monosperma [Englem.] Sarg.) with goats, defoliation of newly established saplings must be enhanced to levels that eventually kill or suppress plant growth. We tested the effect of stocking density and mixed grazing with sheep as potential grazing strategies to increase utilization of one-seed juniper saplings by goats. In summer and spring, groups of 10 does (Goats alone, GA) or 5 does and 4 ewes (Mixed grazing, MG), grazed 20 x 30 m cells infested with saplings (500-533/ha; 0.8 m tall), either continuously for 6 days (Low stocking density, LD) or with daily rotation through 10x10m cells during the 6 day period (High stocking density, HD) in a block design. Frequency of saplings with light, moderate and heavy bark and foliage use, feeding activity, juniper in feces, and utilization of herbaceous vegetation were determined. Goats in HD treatment spent more time feeding on saplings, less time feeding on herbaceous forages, and tended to achieve diets with more juniper than goats in LD. Utilization of herbaceous vegetation ranged from 52 to 73% and was higher for MG than GA and for LD than HD. The MG-HD treatment resulted in highest frequency of short saplings (< 0.5m) with high percent (> 66%) of defoliated branches in summer and spring, and lowest frequency of saplings with low percent (< 33%) of debarked branches in spring. Heavy defoliation was more frequent in shorter saplings, whereas heavy debarking occurred mostly in tall saplings. The results of this study suggest that stocking density and mixed grazing stimulate feeding behaviors that increase utilization of juniper saplings by goats.