Woodlands dominated by Utah juniper (Juniperus osteosperma) have been expanding into grassland and steppe vegetation during the past century in central and southwestern Wyoming. This expansion has occurred during a period of intensive grazing and climate change, and is superimposed on a longer-term range expansion of the species that has been occurring for several thousand years. Juniper woodland expansion has important ecological consequences and management implications.
We are studying the patterns and mechanisms of Utah juniper expansion across a range of scales, both temporal (decades to millennia) and spatial (local stands to statewide), using a variety of ecological, paleoecological, and historical methods. Studies of fossil packrat middens are revealing the patterns and rates of long-term expansion of Utah juniper across the state during the past 10,000 years. These studies are also helping assess community-level impacts of Utah juniper invasion, and documenting long-term climatic changes.
Demographic studies of existing Utah juniper woodlands are being used to help determine the timing of cohort establishment events, and assess whether recruitment is continuous or episodic. Studies of tree-ring records are providing a detailed climate history for central Wyoming that can be applied toward assessing effects of climatic change on the population dynamics of junipers and other woody species.
An example pair of repeat photographs. Click on either
image to get a higher-resolution version.
Repeat ground photography, in which we relocate historical photographs (dating to the late 19th and early 20th Centuries) and reshoot the images, are providing detailed assessments of woodland expansion during the past century. Repeat aerial photography, in which recent aerial photographs are compared with archival aerial photos (1940s-1970s) from the same regions, are providing quantitative estimation of patterns, rates, and magnitude of woodland invasion. Finally, ecological modeling is indicating the critical variables that influence Utah juniper distribution today and identifying critical regions where future invasions might occur.
The project is funded by the National Science Foundation Ecology Program (DEB-9806574), and is co-directed by Stephen T. Jackson (University of Wyoming) and Julio L. Betancourt (U.S. Geological Survey and University of Arizona). Other personnel include:
You can now download the final NSF report for the Utah Juniper Project: NSF-DEB-9815500- Final Report, Collaborative Research, "Late Holocene Expansion of Utah Juniper in Wyoming: A Modeling System for Studying Ecology of Natural Invasions", in Adobe pdf format.
Other e-mail contacts:
Julio Betancourt: jlbetanc@usgs.gov
Stephen Jackson: jackson@uwyo.edu