Invasive Species
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Proper grazing management appears urgent in preventing or delaying further encroachment of cheatgrass (Bromus tectorum) into perennial vegetation on western grazing lands and subsequently gaining site dominance. In mixed stands with desirable perennials, livestock grazing might be directed to (1) reducing cheatgrass competition by concentrating grazing of cheatgrass during dough seed stage, providing perennials still have opportunity to complete their life cycles, or (2) basing grazing on the needs of perennials while mostly ignoring cheatgrass. When cheatgrass domination results in a closed community, alternatives appear limited to (1) managing as annual grassland, or (2) revegetation using intensive cultural practices. In conjunction with revegetation, livestock might conceivably be employed for “graze out” in site preparation and I or for selective plant control during germination and emergence of the seeded perennials. However, with these possible limited exceptions, grazing is concluded not to be an effective general tool for cheatgrass control.
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This paper provides a historical perspective of the influence of cheatgrass invasion on western rangelands (1930-1950). This was a period of awakening interest by range scientists. Range managers, the livestock industry, and scientists have always bad a love-bate relationship with cheatgrass. It provides the bulk of the forage on many ranges, yet it is the symbol of environmental degradation. Trying to cope with the endless ramifications of cheatgrass invasion, dominance, persistence, and potential community decline keep forcing scientists to critically evaluate the ecological principles upon which range management is based.
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The range livestock industry has adapted to the presence of invasive annual grasses, especially where infestations are extensive. Light to moderate livestock grazing provides enough standing grass at the end of the grazing season to limit soil erosion and conserve soil moisture and nutrients. Elsewhere, however, where infestations of invasive annual grasses are less extensive or less advanced, opportunities exist for using targeted, or prescribed, livestock grazing to suppress annual grass plants. This chapter focuses on using prescribed livestock grazing to suppress invasive annual grasses on sites where these grasses are considered weedy invaders.
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Although this study helped pinpoint optimal defoliation parameters for cheatgrass control, it also called into question the potential for livestock grazing to be an effective seed-bed preparation technique in native plant reseeding projects in cheatgrass-dominated areas.
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Cattle removed 80 to 90% of standing biomass in grazed plots in May of 2005 and 2006 when B. tectorum was in the boot (phenological) stage. Grazed and ungrazed plots were burned in October 2005 and 2006. The combined grazing–burning treatment was more effective than either treatment alone in reducing B. tectorum seed input and seed bank density, and in shifting species composition from a community dominated by B. tectorum to one composed of a suite of species, with B. tectorum as a component rather than a dominant. This study provides a meso-scale precursor for landscape-scale adaptive management using grazing and burning methodologies.
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Grazing exacerbates Bromus tectorum dominance in one of North America’s most endangered ecosystems by adversely impacting key mechanisms mediating resistance to invasion. If the goal is to conserve and restore resistance of these systems, managers should consider maintaining or restoring: (i) high bunchgrass cover and structure characterized by spatially dispersed bunchgrasses and small gaps between them; (ii) a diverse assemblage of bunchgrass species to maximize competitive interactions with B. tectorum in time and space; and (iii) biological soil crusts to limit B. tectorum establishment. Passive restoration by reducing cumulative cattle grazing may be one of the most effective means of achieving these three goals.
View fact sheet, pg. 9.
This fact sheet provides managers with strategies to reduce the spread and impact of medusahead.
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View fact sheet, pg. 12.
This fact sheet provides managers with tools and strategies to reestablish perennial-dominated plant communities in medusahead-invaded sagebrush rangelands.
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Land managers are increasingly interested in improving resilience to disturbances,such as wildfire, and resistance to invasive species,such as cheatgrass and medusahead. This fact sheet is designed to assist land managers in resilience and resistance concepts to assess risks, prioritize management activities, and select treatments.
This is the first of many topics reviewed in the Great Basin Fact Sheet series.
Individual fact sheets comprising the Information and tools to conserve and restore Great Basin ecosystems – Factsheet Series are available below.
No. 1- Putting resilience and resistance into practice
No. 2- Limiting medusahead invasion and impacts in the Great Basin
No. 4- Conifer removal in the sagebrush steppe: The why, when, where, and how
No. 6- Wind erosion following wildfire in Great Basin ecosystems
No. 7- Post-fire grazing management in the Great Basin
No. 8- Establishing big sagebrush and other shrubs from planting stock
No. 9- Assessing fuel loads in sagebrush steppe and PJ woodlands
No. 10- Seeding big sagebrush successfully on Intermountain rangelands
No. 11- Assessing impacts of fire and post-fire mitigation on runoff and erosion from rangelands
No. 12- Management of aspen in a changing environment
No. 13- Woody fuels reduction in Wyoming big sagebrush communities
No. 14- Seeding techniques for sagebrush community restoration after fire