Western jumper has been part of the landscape in the eastern Oregon region for thousands of years. Junipers began to expand their range aggressively in this region as well in Northeast California, Northwest Nevada, and Southeast Idaho between 1890 and 1900. These areas of expansion are considered new woodlands and occupy an area 10 to 15 times the size occupied in the previous century.
Old or original juniper woodlands are present throughout the region. Trees in these sites may be 600 to 800 years old. They are part of the overall landscape ecology. Recruitment of younger trees on these sites appears to be very slow.
Expansion of junipers into new woodlands is a result of climate, fire and grazing. Following the end of the Little Ice Age (circa 1850) winters became more mild and precipitation increased through the early 1900s. These conditions were ideal for cone production and seedling establishment. At the same time, fire intervals were reduced with the introduction of livestock and the subsequent reduction in fine fuels associated with livestock grazing. Small isolated stands changed to large contiguous woodlands.
An ecosystem containing juniper functions differently than one without juniper. Particularly noticeable are the changes in the water and nutrient cycles. As western jumper increases in number and size, a larger proportion of the water falling on a site is affected by canopy interception and the overland flow of water. On sites in Central Oregon, interception loss from the canopy cover was as high as 20% or two inches per year in a 10-inch precipitation zone (LE. Eddleman and P.M. Miller. Potential impacts of Western Juniper on the Hydrologic Cycle. Symposium on Ecology and Management of Riparian Shrub Communities, Sun Valley, ID, May 29-31, 1991).
Junipers are effective in using available moisture and also use water very early in the spring before other plants begin to grow. On a warm April day, individual trees can use up to 20 gallons per day. In Central Oregon it was demonstrated that juniper trees were using over 12.6 inches of water in a precipitation zone of 15 inches. This site had a density of 26 trees per acre over six inches in diameter and 454 trees less than six inches. This left 2.4 inches available for other plant growth for the entire year which is simply insufficient. Soil moisture is often limited for these plants by June 15 whereas in sites without juniper, soil moisture is available through August. Juniper competition leads to fewer plants, less soil cover, lower water infiltration rates, more opportunity for overland flow and soil erosion, greater nutrient loss, and a less productive site both from the standpoint of plant species and animal species richness and abundance.
It is clear that new juniper woodlands pose a critical threat to watershed and ecosystem health on many Eastern Oregon sites. Once juniper becomes dominant, only its removal benefits watersheds. Succession over the long term may not be significantly affected by grazing or not gazing. Careful grazing management can only slow the rate of juniper increase. Poor grazing management markedly increases the rate regardless of the time of year grazed. More direct control measures are probably necessary.
Juniper management approaches vary but an outcome-oriented approach is important to consider. Other approaches which involve removing juniper are often shortsighted and result in a more impoverished condition than with juniper dominating. The outcome-oriented approach examines:
On severely degraded sites, junipers need to be cut and the limbs scattered after seed has been introduced. Other sites may have enough existing native grasses such that removing the junipers will provide the necessary kick-start to the system, providing sufficient time is allowed for plants to increase in vigor, set seed, and for resultant seedlings to establish and reproduce.
Grazing, if one of the objectives. should be timed to benefit desirable plants. Cam will have to be given to new plants as they are very susceptible to damage.
At some point in time, fire will have to be reintroduced into the ecosystem Small trees are often present after a cut-and-scatter and need to be controlled. A fairly long time period may be available for fire use. Trees under five to six feet in height can be burned successfully when sufficient fuels are present. Also, since fire once helped develop the ecosystem, it can still play a beneficial role as a maintenance tool in subsequent management.
In many instances the issue is not how to kill western juniper, as juniper has many values. The issue is how to manage resources to promote a healthy, functioning ecosystem that sustains itself without causing damage to the site. The condition of a site reflects past practices. Fire suppression, mismanagement of cattle, climatic changes and other factors have all contributed to the situation we now face. Proper grazing practices based on watershed needs and animal behavior must be established. Fire must be reintroduced into the system to maintain the correct mix of shrubs and grasses.
For more information, contact Clint Jacks, OSU Extension Service, Jefferson County (541) 475-3808.