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Some native conifers in the Sagebrush Sea are unnaturally expanding into sagebrush steppe due primarily to the introduction of domestic livestock grazing and the exclusion of fire in the past 150 years. Invading juniper, pinyon and pine species require less water than most tree species and they thrive in the Sagebrush Sea's limited moisture conditions and higher (but not too high) elevations.

Threats from Western Juniper Encroachment

An old-growth western juniper on a rocky ridgetop and a young post-settlement western juniper woodland in the background on Steens Mountain, Oregon - Biology, Ecology and Management of Western Juniper

Western juniper occurs in Oregon, Idaho, California, Washington, and Nevada. The species grows slowly and trees can live over fifteen hundred years. Under natural conditions western juniper remains in balance with sagebrush, grasses, wild flowers and sedges in the Sagebrush Sea. Historically, individual trees were found clinging to rocky ridges where they were spared by periodic wildfire. However, decades of livestock grazing, fire suppression and other factors have created conditions that scientists believe have contributed to the rapid and unnatural spread of western juniper down from the hilltops and across sagebrush basins. Restoration of natural fire regimes and the elimination of livestock grazing will help restore a balance in the Sagebrush Sea that will benefit sagebrush steppe and Sagebrush Sea wildlife, such as sage-grouse.

The Sagebrush Sea Campaign has published Managing Western Juniper to Restore Sagebrush Steppe and Quaking Aspen Stands that describes western juniper expansion and presents management recommendations to reverse western juniper encroachment in the Sagebrush Sea.

Abstract: Since 1870, concurrent with the introduction of domestic livestock and the resultant exclusion of periodic fire, the occurrence of western juniper (Juniperus occidentalis) in the sagebrush steppe has increased approximately ten-fold. Sagebrush (Artemisia spp.) habitat is being converted to western juniper woodland at a geometric rate. Western juniper is also invading and replacing quaking aspen (Populus tremuloides) stands. Action is needed to reverse these trends and restore sagebrush steppe and quaking aspen stands to an ecologically intact landscape maintained by periodic fire. Western juniper control must spare all old-growth western juniper trees. Restoration planning and implementation must carefully consider the eff ects of invasive non-native species-particularly cheatgrass (Bromus tectorum)-and livestock grazing on treated sites. The conservation community should advocate for appropriate, ecologically based western juniper management and oppose inappropriate actions and strategies.

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Western juniper invading sagebrush steppe from distant hilltop (smallest visible  juniper trees highlighted in boxes) (notice the burn line dividing sagebrush from grass community, and juniper snags killed by fire in burned area). PRBO Conservation Science Shrubsteppe Monitoring Program

Western juniper invading sagebrush steppe. Notice juniper covers distant hills. The sagebrush habitat pictured here is also degraded by livestock grazing and fragmented by (1) agricultural conversion (2) transmission lines and (3) roads. PRBO Conservation Science Shrubsteppe Monitoring Program

Western juniper descending from desert ridges and converting sagebrush steppe to western juniper woodland near Paisley, Oregon. The snags were created by fire, but more prescribed or natural fire is needed to clear these hillsides of invading juniper. The Larch Company

The absence of periodic fire allows western juniper to invade even ungrazed (by domestic livestock, although previously grazed for decades) sagebrush steppe on Hart Mountain National Antelope Refuge. The Larch Company

Pronghorn and western juniper in Hart Mountain National Antelope Refuge. If left uncontrolled, western juniper may become a dominant component of sagebrush steppe in this area, replacing and/or rendering sagebrush steppe unusable to pronghorn and other sagebrush obligate species. However, the sparse distribution of western juniper in this case may allow for quick, easy, and successful control of western juniper for relatively little cost. The likely presence of cheatgrass or other invasive weeds in the area may weigh against using broadcast burning to control these trees and torching individual trees under the right weather and moisture conditions may be preferred. Because livestock grazing is prohibited on Hart Mountain National Antelope Refuge, the healthy sagebrush steppe and a natural fire regime will help prevent western juniper encroachment in the future. The Larch Company

Two examples of western juniper control in the Chewaucan River Basin, Oregon: cutting and spot (single-tree) burning. The Larch Company

Old-growth western juniper must be protected from control activities. Biology, Ecology, and Management of Western Juniper