Targeted Livestock Grazing to Suppress Invasive Annual Grasses

Invasive annual grasses are a serious problem on North American rangelands. These undesirable species, such as cheatgrass (or downy brome), Japanese brome, and medusahead, often out-compete desirable perennial species. Invasive annual grasses can form nearly pure stands that exclude most other plants, decrease biological diversity and forage production, and increase soil erosion. In some areas, invasive annual grasses also create continuous fine fuel loads that promote wildfires more frequent than native shrubs and perennial grasses can tolerate.

Invasive annual grasses, especially cheatgrass, have a self-perpetuating relationship with fire. Fire creates conditions that favor their growth, which, in turn, creates fine fuel loads that favor subsequent wildfire. Targeted livestock grazing can help diminish this fire hazard by disrupting fine fuel continuity and reducing fuel loads.

Sheep, goats, cattle, and horses readily consume grass-dominated diets, provided grasses are plentiful. All four of these livestock species can be used to suppress invasive annual grasses. Sheep and goats can be particularly effective because their grazing can be closely controlled by herding or confined with portable electric fence. The heavy grazing intensities required to suppress many annual grasses are easier to manage when livestock can be confined in small grazing areas. Effective management also requires applying grazing at the appropriate time, a precision more easily achieved when a herder can manage the animals. With their larger mouths, cattle and horses may not select annual grasses as readily as sheep or goats because livestock prefer plants they can eat quickly and efficiently.

Whether targeted livestock grazing achieves its desired effect depends on a manager's ability to apply the appropriate levels of defoliation at the proper times. Identifying the best time to graze is by far the most important decision determining success or failure in suppressing annual grasses. Annual grasses reproduce by seed; therefore, invasive annual grasses can be suppressed when targeted livestock grazing limits their production of viable seeds. Seedheads of invasive grasses must be removed while they are still green, before seeds reach the dough stage. In Michigan alfalfa fields, for example, cheatgrass was controlled by livestock grazing in late April and early May, but control failed when grazing was delayed until after May 15.

Grazing annual grasses several times during spring growth is an important and often essential element of an effective management strategy. Cheatgrass, for example, usually requires a second or third grazing in spring because it can regrow and produce new seedheads about three to four weeks after the first defoliation.

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