Peterson, Eric B. .
Invasion of the Annual Grasses: Mapping the Loss of Nevada’s Ecological Integrity.
MUCH of the native ecosystems in California’s Central Valley were converted long ago to exotic annual grasses. The intermountain west, including Nevada, is now experiencing a similar conversion; the ‘sagebrush sea’ is gradually becoming the ‘cheatgrass sea’. These grasses invade many landscapes after disturbances including wildfire, forming dense stands with fine fuels that shorten typical fire intervals. Thus annual grasses and wildfire form a positive feedback mechanism that propels them through native ecosystems. Nevada and the Intermountain West include vast areas of public land and there is potential for land managers to strategize against complete loss to annual grasses. Implementing strategies will require detailed knowledge of the geographic distribution of annual grasses. An annual grass index map (ANGRIN) for the entire state of Nevada has now been completed. The ANGRIN map is derived from censored regression models utilizing percent ground-cover data at 806 training sites statewide, multitemporal satellite sensor data (Landsat 5 and MODIS) for distinguishing annual grass phenology, and accessory data including elevation. Primary annual grasses found at the training sites were Bromus rubens, Bromus tectorum, and Schismus barbatus. The resulting ANGRIN map provides a strong view of the current status of annual grass invasion in the state of Nevada. Accuracy assessment included the use of the training data set from the Southwest Regional Gap Analysis Project (REGAP). In comparing the ANGRIN mapped values with the percent ground-cover at REGAP plots showed a root-mean-squared discrepancy in ground cover of 10.33 %; 75 percent of ANGRIN predictions were off by 5 % or less; and 95 % of ANGRIN predictions were off by 21 % or less. Similar methods are currently being employed to extend the map into southwestern Idaho and southeastern Oregon.
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Nevada Natural Heritage Program
Mapping Report and GIS data
1 - Nevada Natural Heritage Program, Department of Conservation & Natural Resources, 901 South Stewart Street, suite 5002, Carson City, Nevada, 89701, USA
Bromus madritensis ssp. rubens
Presentation Type: Oral Paper:Papers for Topics
Date: Tuesday, August 1st, 2006
Time: 2:45 PM