The expansion of trees into sagebrush
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In most cases, we think of more trees as more of a good thing and, in most cases, that is true.
However, in sagebrush country, sagebrush bushes were historically the largest plants on the landscape. The fast-paced encroachment of conifer trees, such as juniper and pinyon pine, into sagebrush habitats is changing the dynamics of this delicate ecosystem in ways that have negative impacts for many species of native wildlife.
The intrusion of conifers into sagebrush is primarily in response to suppression of natural wildfire cycles, intensive livestock grazing, and changes in the climate. Conifers are anticipated to continue their expansion in the future unless effectively treated, with the most pronounced risks occurring in the Great Basin (western) portion of the sagebrush ecosystem.
Trees that encroach into sagebrush habitat disrupt the ecosystem, and have been shown to:
- Shade out native perennial grasses and forbs. This may increase annual weed cover.
- Contribute to reduced water availability. The trees utilize water and nutrients and their expansion causes a loss of perennial grasses and forbs, which, in turn, causes an increase in surface water runoff and erosion.
- Negatively affect the survival rate of nesting birds. Raptors and ravens, which are predators of some nesting birds, use the trees as perches. For example, in Utah, 86% of greater sage-grouse hens avoided nesting in sagebrush habitat invaded by conifers. With conifer removal, they were most likely to successfully fledge their broods.
- Increase fuel available for wildfires. This then increases the risk of invading cheatgrass entering the ecosystem after the fire.
Treatment methods include cutting, mastication, prescribed burning, and herbicide application. These treatments have different costs and varying impacts on the desirable plant species and degree of surface disturbance.
Proactive removal of conifers during early phases of invasion, with minimal ground disturbance and retaining perennial shrub and herbaceous communities, is the most cost-effective treatment and reduces risk of invasive annual grasses moving in post-treatment. In addition, the greater the cover of perennial grasses and forbs prior to treatment, the greater the likelihood the system can resist invasion by cheatgrass.
As with all conservation issues in sagebrush country, communication and collaboration with our county, state, and federal partners, as well as private landowners, is critical to our success.
- A Sage Grouse Initiative Report: Conifer Removal Boosts Sage-Grouse Success
- Woody invasion of western rangelands: Using grouse as focal species for ecosystem restoration (published in the scientific journal Rangeland Ecology & Management)