Introducing cattle grazing to a noxious weed-dominated rangeland shifts plant communities

Abstract

Invasive weed species in California's rangelands can reduce herbaceous diversity, forage quality and wildlife habitat. Small-scale studies (5 acres or fewer) have shown reductions of medusahead and yellow starthistle using prescribed grazing on rangelands, but little is published on the effects of pasture-scale (greater than 80 acres) prescribed grazing on weed control and plant community responses. We report the results of a 6-year collaborative study of manager-applied prescribed grazing implemented on rangeland that had not been grazed for 4 years. Grazing reduced medusahead but did not alter yellow starthistle cover. Medusahead reductions were only seen in years that did not have significant late spring rainfall, suggesting that it is able to recover from heavy grazing if soil moisture is present. Later season grazing appears to have the potential to suppress medusahead in all years. In practice, however, such grazing is constrained by livestock drinking water availability and forage quality, which were limited even in years with late spring rainfall. Thus, we expect that grazing treatments under real-world constraints would reduce medusahead only in years with little late spring rainfall. After 10 years of grazing exclusion, the ungrazed plant communities began to shift, replacing medusahead with species that have little value, such as ripgut and red brome. The spread of invasive weeds changes plant community composition and can lead to shifts in soil moisture and nutrient availability as well as the suppression of both native plants and other desirable and more palatable nonnatives, thereby reducing herbaceous diversity, wildlife habitat, forage quality and agricultural productivity (DiTomaso 2000;Eviner et al. 2010;George 1992). Across California's annual rangelands, noxious weeds have been estimated to reduce livestock carrying capacity by as much as 50% to 80% (DiTomaso 2000;George 1992;Hironaka 1961;Major et al. 1960). Research Article

Livestock grazing and topographic site effects on grassland plant communities after long-term grazing cessation

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“…In this case, the presence of grazing not only provided opportunities for natives by removing physical barriers for establishment (e.g. Wilsey and Martin 2015), but it also provided indirect opportunities for natives by reducing the competitive ability of invasives (Davy et al 2015).…”

“…Plant communities are expected to change in the presence of grazing both because plants differ in their tolerance to tissue removal as well in their response to changes in competitive dynamics that largely result from altered light conditions (Augustine and McNaughton 1998). For example, in grasslands, the presence of grazing can drive patterns of community assembly (Alberti et al 2017), species richness (Bakker 1998;Rambo and Faeth 1999), rare plant abundances (Pykälä 2003), and invasive species (Davy et al 2015). Although studies demonstrating relationships between grazing and plant communities in working and natural landscapes are well documented, much of this work focuses on desirable forage and invasive species.…”

The use of strip-seeding for management of two late-season invasive plants

“…The presence of invasive plants can reduce land value by inhibiting biodiversity, depressing forage productivity, and depleting soil and water resources (Duncan et al., 2004). However, typical invasive species management approaches such as prescribed fire, herbicide application, mowing and targeted grazing might not be compatible with current rangeland practices or they might demonstrate limited utility in significantly reducing invasive plant cover and reproduction (e.g., Davy et al., 2015; James et al., 2015). Feasible, cost-effective weed management strategies must be identified through science-based methods to facilitate widespread, successful control of invasive plants by land owners and land managers in rangeland systems (e.g.…”

Riparian Meadow Response to Modern Conservation Grazing Management

“…Society has strong contemporary expectations for stewardship of grasslands and meadows to balance agricultural goals with social, cultural, and conservation goals in a changing environment (Briske 2011 ). There is clear evidence that livestock can be managed to conserve and enhance ecosystem services in grazed landscapes (e.g., Davy et al 2015 ; Matejkova et al 2003 ; Middleton et al 2006 ; Pyke and Marty 2005 ; Rosenthal et al 2012 ). There is also clear scientific evidence that unmanaged, excessive grazing can degrade ecosystems and associated goods and services (Belsky et al 1999 ; Eldridge and Greene 1994 ; Fleischner 1994 ).…”