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Relationships Between Western Juniper (Juniperus occidentalis) and Understory Vegetation

Published online by Cambridge University Press:  20 January 2017

D. E. Coultrap ,
K. O. Fulgham ,
D. L. Lancaster ,
J. Gustafson ,
D. F. Lile  and
M. R. George
D. E. Coultrap
Affiliation:
Department of Plant Sciences, University of California, Davis, CA 95616
K. O. Fulgham
Affiliation:
Department of Forestry and Wildland Resources, Humboldt State University, Arcata, CA 95521
D. L. Lancaster
Affiliation:
Department of Plant Sciences, University of California, Davis, CA 95616
J. Gustafson
Affiliation:
USDA Natural Resources Conservation Service, Davis, CA 95616
D. F. Lile
Affiliation:
Department of Plant Sciences, University of California, Davis, CA 95616
M. R. George*
Affiliation:
Department of Plant Sciences, University of California, Davis, CA 95616
*
Corresponding author's E-mail: mrgeorge@ucdavis.edu
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Abstract

Western juniper has been actively invading sagebrush plant communities for about 130 yr. Western juniper canopy cover generally increases as western juniper invades sagebrush steppe communities and succession progresses toward a western juniper woodland. Our goal was to estimate the impact of juniper invasion and canopy increase on understory vegetation structure and productivity on 101 sites in northeastern California. The primary objectives of this study were to: (1) examine the influence of increasing western juniper canopy cover on the composition and productivity of understory vegetation; and (2) assess the effects of western juniper removal on understory vegetation. Sites in early, mid-, and late successional stages and sites on the same soils that had not been invaded were selected. Sites where western juniper had been removed by prescribed fire, mechanical, or chemical methods were compared to adjacent untreated sites. Western juniper canopy cover, understory cover and species composition, productivity, and bare ground were determined at each site during May through July 2005 and 2006. Regression analysis was used to evaluate the relationship between western juniper canopy cover and understory vegetation parameters. Logistic regression was used to detect understory differences between treated (juniper removed) and untreated (juniper not removed) sites. A significant relationship was found between western juniper canopy cover and understory species richness, shrub cover, forb cover, total grass cover, cheatgrass cover, herbaceous productivity, and bare ground. Removal of western juniper increased total grass cover, cheatgrass cover, and productivity, and reduced bare ground. The results of this study support findings by researchers in other states that western juniper influences plant community structure and productivity, and removal of western juniper might reverse these changes in structure, but also might increase opportunities for invasion of cheatgrass.

Keywords

Western juniper, Juniperus occidentalis var. occidentalis Hook.sagebrush, Artemisia tridentata Nutt.cheatgrass (Bromus tectorum L.)Successionspecies richnesscoverproductivitybare ground
Type
Research Articles
Information
Invasive Plant Science and Management , Volume 1 , Issue 1 , January 2008 , pp. 3 - 11
Copyright
Copyright © Weed Science Society of America 

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