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Abstract
The Response of Cheatgrass (Bromus tectorum L.) and Native Flora to Ecological Manipulations in the Yellow Pine-Mixed Conifer Forest
Thomas W. McGinnis, U.S. Geological Survey, Biological Resources Discipline, Western Ecological Research Center, Sequoia-Kings Canyon National Park, Three Rivers, CA 93271, ph: (559) 565-4262, email: tmcginnis@usgs.gov. Jon E. Keeley, U.S. Geological Survey, Biological Resources Discipline, Western Ecological Research Center, Sequoia-Kings Canyon National Park, Three Rivers, CA 93271. Matt Brooks, U.S. Geological Survey, Biological Resources Discipline, Western Ecological Research Center, Las Vegas Field Station, Las Vegas, NV 89119. Robert Sanford, Department of Biological Sciences, University of Denver, Denver, CO 80208. Jayne Belnap, U.S. Geological Survey, Biological Resources Discipline, Forest and Rangeland Ecosystem Science Center, Moab, UT 84532.
Manifest Destiny opened up the west to settlers and their weeds, and one of the most persistent weeds in western rangelands is cheatgrass. Burned areas are quickly colonized by cheatgrass as isolated satellite populations spread their seeds into these newly disturbed lands. Although the areas west of the Sierra Nevada Mountains have long been converted to non-native annual grasses, such as Bromus and Avena, and cheatgrass commonly invades east of these mountains, in the Great Basin, the forests in between were once thought to be immune to annual grass invasions. Although cheatgrass has been known to exist along roads and trails in these mountains for some time, widespread invasions in the yellow pine forest were unheard of in the past. Today, large expanses of these forests are becoming carpeted by cheatgrass. One such area of widespread invasion is the Cedar Grove area of Kings Canyon National Park, where our study takes place.
Because we do not know what disturbance factors trigger cheatgrass invasions in these forests, we do not know how to prevent its invasion. In 408 randomly assigned 5x5 m test plots (six replicate sites), we are intensifying several disturbance factors in order to determine how each affects cheatgrass and native plant cover. Plots either remain unburned, or are burned in one of three burning seasons. Before and after each burning season, soils are tested to see how temperatures affect soil nutrients. Temperatures are monitored above and belowground using six thermocouples per plot. Plots are assigned one of the following manipulations: no addition, pine litter addition, 50% shade, added or reduced nitrogen, added or reduced phosphorous, cheatgrass seed addition, or native seed addition. Although no manipulation following the low-intensity Fall 2001 burns resulted in the elimination of cheatgrass, it is expected (after observing the unmanipulated forest surrounding these plots) that the addition of 5 cm of pine needles, a treatment added in 2002, will eradicate cheatgrass. Other plant cover changes will be discussed relative to each disturbance factor.
