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Dynamics of Utah Juniper Woodlands in Wyoming

Dynamics of Utah-Juniper Woodlands in Wyoming

Roles of Dispersal, Climate, Land-Use, and Population Processes

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.

Picture of Juniperus Osteosperma.
Juniperus Osteosperma

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.

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.

Figure 2a.
Figure 2a. 1904 Darton photo (#1003) of the "Tensleep and Amsden formations on west side of Tensleep Canyon, Bighorn Mountains. Looking northeast. Shows Tensleep Sandstone and basal cross-bedded sandstone of Amsden on Little Horn Limestone." The foreground vegetation, where Darton's horses are grazing, is mostly sagebrush. The riparian gallery along Tensleep Creek includes cottonwoods and willows. The larger trees dotting the hillside are ponderosa pine, whereas the smaller shrubs include Utah juniper and little-leaf mountain mahogany. Darton took this photograph from a wagon road in Tensleep Canyon.

Figure 2b.
Figure 2b. 22 August 1998 photo and data taken by Steve Tharnstrom and Julio Betancourt (Station 99 matches Darton #1003; N44°3.828' W107°22.152'; Washakie Co., Wyoming, 1429 m elevation). Note that the sagebrush has been replaced by grasses in the foreground and both Utah and Rocky Mountain junipers. The greatest change is on the hillslope and cliffsides, which are being invaded by Utah juniper. The wagon road has now been replaced by U.S. Highway 16.

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. 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 pdf format (511 KB).

Other e-mail contacts:

Julio Betancourt:
Stephen Jackson:

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