چرای هدفمند گل گندم زرد در منطقه آیداهو در اواخر فصل توسط دام (بز) Late-Season Targeted Grazing of Yellow Starthistle (Centaurea solstitialis) with Goats in Idaho

Invasive plants cause tremendous ecological and economic loss on rangelands (Duncan and Jachetta 2005). Yellow starthistle (Centaurea solstitialis L.) is a particularly challenging invasive winter annual that is one of the most problematic and widespread plants in the United States (DiTomaso 2000), infesting almost 6,000,000 hectares in the western states (Duncan and Jachetta 2005). Major infestations exist in California, Idaho, Oregon, and Washington. Yellow starthistle has been increasing in abundance since 1970 (Maddox et al. 1985) and is spreading at an annual rate of 13 to 17% (Duncan and Jachetta 2005). Yellow starthistle can form dense stands that are avoided by most livestock and wildlife species (Thomsen et al. 1993). Yellow starthistle creates fuel loads for wildfires (Thomsen et al. 1997) and degrades recreational value and biodiversity (Balciunas and Villegas 1999; Benefield et al. 1999). Yellow starthistle has the ability to impact community structure and function by displacing native and sometimes rare plant species, by altering wildlife populations, and by modifying fuel characteristics and soil moisture levels (Duncan and Jachetta 2005). Yellow starthistle also invades grain fields, orchards, vineyards, cultivated crops, pastures, roadsides, and wastelands and can contaminate alfalfa, cereal grains, hay, and commercial seed (Maddox and Mayfield 1985). Yellow starthistle spreads primarily with disturbance but can also spread to undisturbed areas (Roche´ et al. 1994), and this accentuates the need for treatment options. A variety of control measures (mainly herbicide) successfully have controlled small infestations. However, yellow starthistle presently infests vast areas of rugged canyon rangelands where inaccessible terrain limits feasibility of some control methods. Targeted grazing using domestic goats might be an effective means for managing yellow starthistle in steep terrain and at landscape scales. Targeted grazing with livestock as a weed management tool has been gaining popularity and has application for many weedy species. For example, goat and sheep grazing can reduce plant densities of spotted knapweed (Centaurea stoebe L.; Olson et al. 1997; Williams and Prather 2006). Sheep and cattle have been used successfully to control leafy spurge (Euphorbia esula L.; Jacobs et al. 2006; Lacey et al. 1984; Olson and Wallander 1998). Goats readily consume yellow starthistle seedheads that have fully developed spines (personal observation). Other livestock have not been observed to consume yellow starthistle in its mature stage (Hovde 2006). Research that has focused on target grazing yellow starthistle has been conducted in small paddocks (Hovde 2006; Thomsen et al. 1989, 1993). Little is known about the usefulness of target grazing yellow starthistle at the landscape scale. Our research objective was to determine whether targeted goat grazing is a viable tool for yellow starthistle management at a landscape scale. Specifically, we evaluated the effect of late-season goat grazing on: (1) plant and seedhead density of yellow starthistle, and (2) canopy cover of yellow starthistle and associated plants in the community