NEPA--Environmental Assessment

Silverton Grazing Risk Assessment
FACTORS CONSIDERED IN THE RISK ASSESSMENT PROCESS
• Bighorn sheep mapped summer range and summer concentration areas (provided
by the Colorado Division of Wildlife):
o Summer range is that part of the overall range where 90% of individual
bighorn sheep are located between spring green-up and the first heavy
snowfall. Summer range is not necessarily exclusive of winter range; in some
areas winter range and summer range may overlap. Summer range does not
necessarily include all occurrences during the summer season.
o Summer concentration areas are those areas where bighorn sheep
concentrate from mid-June through mid-August. High quality forage,
security, and lack of disturbance may be characteristic of these areas to
meet the high energy demands of lactation and lamb rearing.
o Mapped production areas were not considered because there is no overlap
between them with active or vacant allotments in the Silverton Landscape.
Mapped winter range areas were not considered because domestic sheep are
not in the allotments during winter.
• Domestic sheep allotment activity status (FS and BLM);
• Changes in allotment boundary configuration (FS and BLM);
• Domestic sheep grazing suitability maps (FS and BLM);
• Vegetation types and topographic features within the allotment (FS and BLM);
• Colorado Division of Wildlife local staff’s professional opinions (District Wildlife
Managers and Terrestrial Biologists);
• FS and BLM local staff’s professional opinions (Wildlife Biologists, Range
Management Specialists, NEPA Specialists, Decision Maker);
• Domestic sheep permittees’ herding practices and bighorn sheep observations;
• Project Design Criteria (see Table 3 attached at the end of this document).
RISK ASSESSMENT OUTCOMES
This Risk Analysis found overlap between mapped summer ranges for wild bighorn sheep
and 8 domestic sheep grazing allotments in the Silverton Landscape (see Figures 1 and 2,
below). The analysis and findings for each allotment and alternative will be discussed
individually and are displayed below in Figures 3 and 4.
Engine Creek/Deer Creek Allotment (FS, active allotment):
Under current management, there is about 2,978 acres of overlap in the allotment with
mapped summer range of the S71 West Needles bighorn sheep herd. Within this area,
about 1,253 acres (42%) is suitable domestic sheep grazing range. Under Alternative 3,
there would be about 3,791 acres of overlap in the allotment with mapped summer range
for S71. Within this area, about 1,293 acres are considered suitable domestic sheep
grazing range, of which 1,122 acres are on NFS lands and 171 acres are on BLM lands.
Under Alternative 3, allotment boundary adjustments would be done specifically to
reduce the total amount of overlap between active and vacant allotments and mapped
summer range for the S71 bighorn sheep herd in the Silverton Landscape. This would be
accomplished, in part, by closing the vacant Little Molas/West Needles Allotment. This
adjustment of the boundary between the active Engine Creek/Deer Creek Allotment and
vacant Little Molas/West Needles Allotment would result in a 21% increase in the area of
overlap in the Engine Creek/Deer Creek Allotment under Alternative 3 (3,791 acres)
compared to Alternative 2 (2,978 acres). The boundary adjustment would also include the
presence of overlap on BLM lands under Alternative 3 that was not present under
Alternative 2. This boundary adjustment however, would provide a more functional
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