Submitted to: Eastern Oregon Agricultural Research Center
Publication Type: Experiment Station
Publication Acceptance Date: November 1, 2003
Publication Date: March 1, 2004
Citation: Bates, J.D. 2004. South mountain juniper control study, annual report, 2003. Eastern Oregon Agricultural Research Center. 17 p. Interpretive Summary: Western juniper expansion into sagebrush steppe plant communities in the northern Great Basin (eastern Oregon, southwest Idaho, northeast California, northwest Nevada) has resulted in diminished shrub-steppe productivity and reduced plant and wildlife diversity, while negatively impacting hydrologic processes. In the past 30 years efforts to restore plant communities in eastern Oregon have focused on removing juniper by mechanical means (chainsaws, bulldozers, chaining) and with prescribed fire. Once juniper woodlands reach about 60-70 years of age they can be difficult to burn because of a lack of grass and shrubs to carry fire. The purpose of this study has been to evaluate the use of cut juniper to provide necessary cured fuels to carry a fire, kill remaining live trees, and restore the native plant community. We assessed what level of cutting was required to eliminate remaining juniper trees by fire in plant communities on South Mountain, southwestern Idaho. Tree cutting manipulations involved chainsaw cutting 25%, 50% and 75% of the juniper trees. Juniper tree cover prior to cutting ranged between 35-70% and tree density was 100-200 trees per acre. Juniper trees were cut in October 2002, allowed to dry for one year, after which prescribed fire was applied to treatment plots in October 2003. Regardless of cutting treatment the fire application was uniformly successful at removing remaining live junipers. On most areas, with similar woodland characteristics, it is estimated that only 15-25% of the trees need to be cut to successfully remove remaining live juniper. This would substantially reduce the cost per acre for removing juniper and would allow larger areas to be treated more cost effectively. The response of the understory the first growing season after fire indicated that recovery was proceeding rapidly. Plant composition was mainly native forbs and grasses. Understory cover was equal to or greater than cover prior to treatment. It is predicted that understory cover will peak by the 4th-5th growing season after fire.
Technical Abstract: Western juniper expansion into the sagebrush steppe diminishes forage production, reduces plant and wildlife diversity, and negatively impacts hydrologic function. In the past 30 years western juniper has mainly been controlled by cutting, using chainsaws, and by prescribed fire. Recently combinations of selective juniper cutting followed by prescribed fire have been used to remove juniper. The selective tree cutting is used to create a fuels base to carry prescribed fire through the remainder of the juniper stand. A main objective of the research was to assess what level of cutting is required to eliminate remaining juniper trees by fire in plant communities on South Mountain Idaho. The treatment components consisted of several levels of cutting manipulations followed by prescribed burning. Tree cutting manipulations were chainsaw cutting 25%, 50% and 75% of the post-settlement trees. Uncut (control) woodlands were located adjacent to cut areas. Control plots will remain as intact woodlands for comparing herbaceous and shrub response to the cutting and burning treatments. Plots were 1.2 acres in size and each treatment was replicated 5 times. Juniper trees were cut in October 2002 and allowed to dry for one year. Temporary livestock exclusion fences were built around plots in spring 2003. Prescribed fire was applied in October 2003. Regardless of cutting treatment the fire application was uniformly successful at removing remaining live junipers. We estimated that on the Deep Soil sites the fire killed all remaining live juniper. On the Dry Soil sites we estimated that the fire killed 85-100% of the remaining live trees. Results indicate that cutting about 25% of mature trees was sufficient to remove the remainder of the juniper stand with fire. Post-fire vegetation monitoring will be performed in 2004-2006, 2008, and 2010. Seeding trials were established on both plant community types, evaluating 6 species (3 grass; Idaho fescue, Sherman big bluegrass, & Goldar bluebunch wheatgrass and 3 forbs; arrow-leaf balsamroot, Lewis flax, and western yarrow). Species are being evaluated individually and in combination at several application rates.