Controlling Western Juniper Encroachment in Sage Grouse Brood Rearing Habitat


Sage Grouse brood

Throughout southern Idaho, sage-grouse populations are threatened by the encroachment of western juniper into sage-steppe habitat. The Sage-grouse Management Plan for Owyhee County lists juniper encroachment among the top three threats to sage-grouse recruitment.

Juniper mastication had not been used in the county because of the remote landscape and cost of operating early mastication machinery. In 2009, The Nature Conservancy, in partnership with the Owyhee Local Working Group, Idaho Department of Fish and Game, and ranchers implemented juniper mastication projects on two significant sites. These projects resulted in the restoration of approximately 526 acres of sage-grouse brood-rearing habitat. Sites 1 and 2 were selected because they are within 3 miles of historic sage grouse leks and were good brood rearing habitat adjacent to wet meadows before being encroached by western juniper. These treatments resulted in a dramatic increase in native plant diversity and abundance the following years. The cost of these mastication treatments was approximately $186 per acre at Site 1, and $245 per acre at Site 2 where larger trees and higher density were encountered. To further demonstrate the effectiveness of juniper mastication we selected a third site at Bull Basin. Site selection was again based on proximity to sage-grouse leks and productive sage-grouse brood rearing habitat. Landowners, George and Donna Bennett, were anxious to remove juniper from this area that was historically heavily used by sage-grouse. In the fall of 2011, 484 acres were successfully restored. The roller-drum masticator operated cost effectively on smaller trees at $82 per acre at Bull Basin (Site 3-a). We anticipate that these mastication treatments will have a 15-20 year lifespan before treatment is again required. Many area ranchers and agency personnel participated in four field demonstrations. Together, these two pilots effectively improve nesting and brood rearing habitat on 1,010 acres in Core Sage-grouse Areas.

Juniper Control Project Bull Basin 1The local Sage-grouse Working Group felt it was especially important to demonstrate both the ecological and cost effectiveness of this alternative juniper control method to landowners and land managers. Both cutting and prescribed fire have been used for juniper management in the Owyhee’s. However many landowners know these conservation practices put their property at risk of fire, weeds and most importantly, expansion of cheatgrass and medusahead. Two types of mastication equipment were tested given that some sites are encroached by older age (stage II) juniper vs. other areas are in early stages (stage I) of  invasion. They found that the roller-drum masticator operated most effectively in young scattered juniper stands that were encroaching wet meadows. In contrast, the larger trees up to 20 inch dbh and over 20 feet tall were most effectively masticated by the excavator machinery. Mobilization costs were similar. Both types of equipment were very light on the land with less than 6 psi track weights. Experienced operators walked the equipment around and over sage in route to juniper trees with very little soil disturbance.

Roller-drum masticator

Roller-drum masticator

As juniper expands into crucial sage-steppe habitat, nesting and brood rearing habitat is disappearing at an increasing rate. Furthermore, sage-grouse and other wildlife are forced to roam ever increasing distances to find safe brood rearing habitat next to surface water. Research has demonstrated that under adequate soil moisture conditions, juniper can consume up to 20 gallons of soil moisture per day per plant. Thus, as juniper increases in density, competition for available soil moisture becomes a much greater factor in sustaining sage-steppe habitat. If left unchecked, key sage-grouse habitat in the Owyhee Uplands will become juniper woodland (Stage 3 ecological site) with little or no understory. Once this ecological condition is reached, a monoculture develops, and the cost of restoration becomes extremely expensive if not impossible. Furthermore, IDFG, Owyhee Sage-grouse Biologist Michelle Kemner has reported that brood rearing habitat in the Owyhee uplands is a major limiting factor in restoring sage-grouse populations in the Owyhee Uplands. She reports that sage-grouse have been observed flying as far as ten miles from leks to locate suitable brood rearing habitat.

Aerial view of juniper mastication one week following treatment - light brown areas are masticated juniper

Aerial view of juniper mastication one week following treatment – light brown areas are masticated juniper

Western juniper is estimated to be expanding at a rate of 2,600 acres per year in the Owyhee’s. Research has shown that just 35 junipers per acre can consume all the available soil moisture in this arid environment. Many of the sites to be restored in the Plan area have juniper densities that exceed 35 trees per acre. Research has demonstrated that removing stage 1 and stage 2 juniper encroachments in shrub-steppe savannas will result in a significant response in preserving sage-grouse habitat. Furthermore, removing juniper around springs and seeps can increase surface water flows as high as 225%. Thus the optimum time to restore crucial shrub-steppe sage-grouse habitat is before Stage 3 conditions develop, and while a viable base of desirable understory vegetation exists. The preferred treatment strategy consists of mechanical removal of Stage 1 or 2 expanding juniper in shrub-steppe habitat through mastication or hand cutting. Because of the need to preserve intact herbaceous vegetation and scenic old growth mahogany savannas, prescribed fire is not a viable option under these conditions. Fire also risks losing sage and increasing invasive weeds and annual grasses.

Contracted services and/or landowner contributions are being used to hand cut or masticate approximately 2,640 acres of Stage 1 and 2 Western Juniper to stump heights of less than 6 inches began on IDL sections just off Mudflat Road in September, 2014 and will be advancing north and west in cooperation with landowners through December of 2016.

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