NEPA--Environmental Assessment
NEPA--Environmental Assessment
NEPA--Environmental Assessment
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The alpine tundra group would benefit most of all the analysis groups from selecting Alternative 1.<br />
Selection of Alternative 1 has the potential to provide direct benefits to two of the three species in<br />
the alpine tundra analysis group (American pipit and white-tailed ptarmigan). The third species in<br />
this group is less likely to have substantial benefit from selecting Alternative 1 because it is less<br />
likely to be directly affected by sheep grazing activities.<br />
Alternative 2<br />
Selecting Alternative 2 would be substantially less beneficial for birds of conservation concern than<br />
selecting Alternative 1, and somewhat less beneficial than selecting Alternative 3, especially for<br />
alpine species. For all bird species of conservation concern, selecting Alternative 2 would generally<br />
maintain current habitat conditions, and for some species, likely result in a gradual long term<br />
improvement in habitat conditions.<br />
Habitat conditions for some bird species is expected to continue to gradually improve under<br />
Alternative 2 because there has been a continued decline in the number of domestic sheep grazed in<br />
the Silverton Landscape. Numbers of domestic sheep grazing in the Silverton Landscape have<br />
dropped about 67% from a high of about 16,000 animals in the 1960’s to about 5,300 currently. In<br />
addition, numbers of sheep grazing on the San Juan National Forest have dropped about 95% from a<br />
high of about 216,600 animals in the 1930’s to about 10,800 currently (SJNF 2009).<br />
Alpine tundra represents about 38% of the habitat in the Silverton Landscape, and about 29% of the<br />
alpine tundra habitat in the landscape is suitable for sheep grazing under current management.<br />
Sheep obtain most of their forage and spend most of their time in the alpine zone. Alpine habitats are<br />
also potentially the most sensitive habitats to livestock grazing because of their very short annual<br />
growing seasons, harsh environmental conditions, frequently shallow soils, and often long time span<br />
for vegetation recovery. The three bird species whose primary habitats occur in the alpine zone<br />
therefore have the potential to be significantly affected by domestic sheep grazing impacts.<br />
Of the three bird species in the alpine tundra analysis group, two (American pipit and white-tailed<br />
ptarmigan) can be directly affected by domestic sheep grazing because they nest on the ground and<br />
forage in areas used by grazing sheep. These two species can be directly affected through the loss of<br />
cover at nest sites, nest trampling by grazing animals, and reduced quality of foraging habitat due to<br />
grazing reducing plant material upon which their insect prey depends (Hoffman 2006, and Versaw<br />
1998). The third species in the alpine analysis group, brown-capped rosy finch, is less likely to be<br />
directly affected by grazing sheep because nests are located in rock cliff crevices and adults forage<br />
mainly on or near snow fields, areas that are actively avoided by domestic sheep (Nelson 1998). For<br />
these three alpine bird species of concern, selecting Alternative 2 would be least beneficial of the<br />
three project alternatives but would result in maintaining current habitat capability or result in a<br />
gradual long term improvement in habitat capability.<br />
Of the seven species in the riparian/wetland group, (American dipper, black swift, cordilleran<br />
flycatcher, and mallard) are unlikely to be affected by sheep grazing. These species usually nest in<br />
places that are inaccessible to sheep such as in dense cover (mallard), adjacent to waterfalls (black<br />
swift), on rock walls overhanging streams (American dipper), and in dirt cut banks (cordilleran<br />
flycatcher). These species also typically forage in areas not frequented by sheep such as in standing<br />
water (mallard) high above the surrounding mountain peaks (black swift), on the floor of rapidly<br />
flowing streams (American dipper), or in the overhead forest canopy (cordilleran flycatcher). For<br />
these reasons, selecting Alternative 2 would have little impact on habitat capability for these four<br />
species in the riparian/wetland analysis group.<br />
The remaining three species in the riparian/wetland group (lazuli bunting, MacGillivray’s warbler,<br />
and Wilson’s warbler) are associated with dense willow and riparian shrublands. Field monitoring<br />
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