|Miller, Richard - OREGON STATE UNIV|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 3, 2005
Publication Date: September 1, 2005
Citation: Bates, J.D., Miller, R.F., Svejcar, A.J. 2005. Long term success trends following western juniper cutting. Rangeland Ecology and Management. 58:533-541. Interpretive Summary: Western juniper encroachment into the sagebrush grasslands and other plant communities' results in reduced forage production, diminishes plant and wildlife diversity, and may cause increased soil erosion. A goal of removing invading juniper woodlands is to restore Northern Great Basin plant communities for livestock production and wildlife habitat. This study assessed the recovery of sagebrush grassland for thirteen years following juniper cutting. Trees were cut in 1991. Production, cover, and densities of understory (grasses and forbs) and shrub species were compared between cut and uncut juniper woodland. Understory production and cover increased in the cut areas over time. Production increased from 40 lb/acre to 1000 lb/acre between 1991 and 1996. Between 1996 and 2004 production of understory plants has been 8-10 times greater in cut areas compared to uncut woodland. Cover of the understory increased 5 fold by the 6th year after cutting and plant diversity doubled. Perennial bunchgrass density increased 4 fold in the cut areas. The results demonstrate that plant communities in the Northern Great Basin can be successfully restored when western juniper woodlands are removed by cutting.
Technical Abstract: Western juniper (Juniperus occidentalis spp. occidentalis Hook.)) expansion into sagebrush steppe plant communities in the northern Great Basin has resulted in diminished shrub-steppe productivity and reduced plant and wildlife diversity, while negatively impacting hydrologic processes. Chainsaw cutting of western juniper woodlands is a commonly applied practice for removing tree interference and restoring shrub and herbaceous composition. Studies reporting understory response following juniper cutting have been limited to early successional stages, usually within the first 2 to 3 years after juniper treatment. This study assessed successional dynamics spanning 13 years following tree cutting. A randomized complete block design, with four 0.9 ha blocks was used to evaluate long-term understory successional dynamics after juniper cutting. Prior to cutting, juniper canopy cover averaged 26% and mature juniper density averaged 250 trees ha-1. Half of each block was cut in late summer 1991. Standing crop, cover, and density of herbaceous functional groups were compared between CUT and WOODLAND treatments. Total herbaceous standing crop, total cover, and perennial grass density increased significantly in the CUT and were greater than the WOODLAND. Total standing crop was 10 times greater in the CUT versus WOODLAND. Herbaceous standing crop and cover, and densities of perennial grasses in the CUT did not change between 1996 and 2004 indicating that by the 5th year after cutting, remaining open areas had been occupied. Though total standing crop in the CUT did not change after 1996, standing crop composition shifted significantly. In the early successional stages, perennial bunchgrasses and Sandberg's bluegrass were dominant. By the 5th year after treatment, cheatgrass had supplanted Sandberg's bluegrass and was co-dominating with perennial bunchgrasses. In 2003 and 2004, the 12th year and 13th year post-treatment, perennial bunchgrasses dominated herbaceous productivity in the CUT, representing nearly 90% of total herbaceous standing crop. A pre-treatment density of 2-3 perennial bunchgrasses m-2 appeared to be sufficient to permit natural recovery of sites after juniper control. Perennial bunchgrass density peaked in the 6th year after treatment and the results suggested that 10-12 plants m-2 were sufficient to fully occupy the site and dominate herbaceous composition in subsequent years. However, in the CUT, juniper rapidly reestablished from seed and from the presence of seedlings not controlled in the initial treatment. Follow-up juniper control will be necessary to maintain herbaceous composition and permit continued reestablishment of the shrub component. The shifts in herbaceous composition across years suggests that long-term monitoring is important for evaluating plant community response to juniper control and to develop appropriate post-treatment management that promote continued site improvement.