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Ecology: How it all works together

Because of its dry climate and cold temperatures, the Great Basin is considered a cold desert. Plants and animals that have long made their homes in this region are specially adapted to the often harsh environmental conditions. Picture of a landscape with willows, sagebrush, and juniper treesThe Great Basin generally has a long, cold winter and most of its precipitation comes as snow. Summers are hot, with little rainfall, and parched winds can sap the soil of moisture. Despite these conditions, more than 400 plant, 200 bird, 70 mammal, and 20 amphibian and reptile species have evolved to tolerate these conditions.


Drawing of arrowleaf balsamroot

Most of the native plants found in the Great Basin are relatively long-lived perennials, and only replace themselves infrequently. Because of this, Great Basin rangelands have gone through cyclical vegetation changes. In sagebrush steppe communities, perennial grasses and forbs are faster growing and dominate first. These herbaceous species are eventually taken over by the longer-lived shrubs. The cycle is complete when a disturbance, usually fire, inevitably occurs and sends the system back to perennial grass and forb dominance. This process is highlighted in the animated cycle.


Image of a fire burningToday, weed introductions have altered this cycle and, in many areas, invasive weeds are stealing the show. Cheatgrass, an annual species, is dominating landscapes once occupied by perennial shrubs, grasses, and forbs. Cheatgrass has partnered with fire to change occasional patchy burns into large-scale infernos that occur more often and earlier in the season. It does this by producing dense stands that dry in mid-summer, providing a continuous fuel to carry fires. Frequent fires reduce the ability of many perennial plants to re-establish, furthering the dominance of cheatgrass. Cheatgrass and fire perpetuate one another and the problem magnifies itself with every reoccurring blaze.


Close-up of diffuse knapweed flowerheadInvasive weeds, including knapweeds, yellow starthistle, rush skeletonweed, medusahead rye, and others find it easier to invade areas degraded by cheatgrass and fire. Like cheatgrass, many of these weeds do well with frequent fire. In addition, these invasive weeds have abilities to injure, out-compete, and overwhelm native plants with a variety of tactics. Cheatgrass and fire weaken or diminish native plant populations, paving the way for secondary weed invasions.

Images:
-Fall colors: Southwest Regional Gap Analysis Project. Field site database. (http://earth.gis.usu.edu/swgap/trainingsites.html, 26 September 2006).
-Drawing: Sagebrush Clips © 2005 Zackery Zdinak.
-Fire:Steve Dewey, Utah State University, http://www.forestryimages.org.
-Diffuse knapweed: Cindy Roche http://www.forestryimages.org.

Text references:
-Briske, D.D., S.D. Fuhlendorf, and F.E. Smeins. 2005 State-and-transition models, thresholds, and rangeland health: A synthesis of ecological concepts and perspectives. Rangeland Ecology and Management. 58(1), pp. 1-10.
-Landres, P.B., P. Morgan, and F. J. Swanson. 1999. Overview of the use of natural variability concepts in managing ecological systems. Ecological Applications, 9(4), pp. 1179–1188.
-Trimble, S. 1989. The Sagebrush Ocean: A natural history of the Great Basin.
-Young, J.A. and W.S. Longland. 1996. Impact of alien plants on Great Basin rangelands. Weed Technology 10:384-391.

Picture of microbiotic crust