Willow cover as a stream-recovery indicator under a conservation grazing plan

Autor: Samuel E. Cox, Eric D. Sant, D. Terrance Booth, Gregg E. Simonds
Rok vydání: 2012
Předmět:
Zdroj: Ecological Indicators. 18:512-519
ISSN: 1470-160X
DOI: 10.1016/j.ecolind.2011.12.017
Popis: Many rangeland streams and associated fisheries have suffered from livestock grazing as a cost of upland-forage utilization. Due to damage from intensive usage, restoration of damaged streams is now a common land-management objective. The Squaw Valley Ranch of Elko County, Nevada, US, in cooperation with the US Bureau of Land Management (BLM) and Barrick Gold Corp., is attempting to improve those portions of the Rock Creek watershed negatively affected by past ranch operations. The watershed includes both historical and occupied habitat for the threatened Lahonton cutthroat trout ( Oncorhynchus clarki henshawi [Richardson]). From 2003, and continuing to the present, hot-season livestock grazing on Squaw Valley Ranch private and permitted public-land riparian areas was greatly reduced. To assess the effectiveness of this conservation effort, we (1) evaluated BLM archived images of riparian photo points in the watershed, (2) tested for change over time using data from systematic, intermittent, aerial sampling that acquired 2-cm resolution images from low-altitude surveys conducted in 2003, 2004 and 2006, and (3) compared Landsat scenes of the area from before and after 2003. Willow ( Salix spp.) cover was chosen as the primary ecological indictor of riparian condition and we introduce willow canopy (m 2 ) per m of stream length in the image field-of-view, as a practical measure of willow status. Archived images from photo points show mostly low-condition riparian plant communities, often with little or no willow canopy evident before 2003, but with conspicuous improvement thereafter. This subjective perception is supported by objective analyses finding, (1) the relative increase in willow cover nearly tripled on one stream, more than doubled on three others, and increased on all but one (fire affected) and (2) a highly significant post-2003 increase in willows in the Landsat record. Thus, the post-2003 increase in willow cover documented in three complementary lines of evidence from ground, air, and space support the predicted ecological benefits of reduced hot-season riparian grazing and the utility of 2-cm imagery as a tool for assessing watershed-wide conservation benefits from a federal cost-share-eligible conservation practice. This appears to be the first use of willow measurements from an aerial survey as a particular indicator of riparian condition and trend and the first demonstration of change detection based on objective measurements from a watershed-scale riparian monitoring effort that used systematic sampling (versus subjective selection) and high sample density to address the large Type II error (false negative) risk common to conventional land-management survey efforts.
Databáze: OpenAIRE
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