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Plant Community Dynamics 25 Years After Juniper Control

Jon D. Bates, Tony Svejcar, Rick Miller, Kirk W. Davies
Rangeland ecology & management 2017 v.70 no.3 pp. 356-362
Artemisia, Juniperus occidentalis, annuals, basins, biomass, chainsaws, cutting, grasses, habitats, invasive species, longevity, perennials, plant density, rangelands, shrubs, steppes, tree classes, trees, woodlands, Oregon
The expansion of piñon-juniper woodlands over the past 100−150 yr in the western United States has resulted in large-scale efforts to kill trees and recover sagebrush steppe rangelands. Western juniper (Juniperus occidentalis spp. occidentalis Hook.) expansion in the northern Great Basin has reduced sagebrush-steppe productivity and habitat. Chainsaw cutting of western juniper woodlands is a commonly applied practice to kill trees and restore shrub-understory composition. Studies reporting vegetation response following juniper cutting have been limited to early successional stages. This study assessed successional dynamics spanning 25 yr following tree cutting on Steens Mountain, southeast Oregon. Herbaceous standing crop and yield and plant densities were compared between chainsaw cut (Cut) and uncut woodland (Control) treatments. Cut plots were treated in 1991. In the Cut, total standing crop and yield have remained fairly consistent since 1996 and on average were 8 times greater than the Control. Perennial grass yield was 2- to 20-fold greater in the Cut than the Control across measurement years and peaked 14 yr (2005) after treatment. Perennial bunchgrass yield declined to 30−40% of its peak value, and bunchgrass density declined from about 11 plants m−2 in 2005 to 7 plants m−2 between 2005 and 2016. Invasive annual grasses increased in yield and as a percentage of total yield from 3% to 20%, between 2005 and 2016. Juniper and shrub cover and density increases and greater annual grass yields in the Cut have likely contributed to declines in perennial bunchgrass density and yields. Juniper control will be necessary within 5 yr to maintain progression to sagebrush steppe, indicating a treatment longevity of about 25−30 yr. To lengthen the life expectancy of cutting and other mechanical control of piñon-juniper woodlands requires that all age classes of trees be controlled in the initial treatment.