NEPA--Environmental Assessment

Silverton Grazing Risk Assessment
Summary of Risk Rating for Needles Mountains Allotment:
Risk Rating: Alternative 2 – High
Alternative 3 – Low - Closed
Under Alternative 2, if the Needles Mountains Allotment were to be stocked, the
substantial area of overlap between known bighorn sheep use areas and suitable
domestic sheep grazing areas results in a rating of “High Risk” for contact. If however, the
allotment were to remain vacant under Alternative 2, the rating would be “Low Risk”
because domestic sheep would not be permitted in the allotment and there would be a low
risk for contact. However, because the allotment could be restocked administratively at
any time, the overall rating of this allotment under Alternative 2 would be “High Risk”.
Under Alternative 3, the Needles Mountains Allotment would be closed to domestic sheep
grazing. The rating would be “Low Risk” because domestic sheep would not be permitted
in the allotment and there would be a low risk for contact.
Flume Allotment (FS, vacant allotment):
Under current management, there is about 653 acres of overlap in the allotment with
mapped summer range for the S71 West Needles bighorn sheep herd. Within this area,
only about 29 acres (4%) is suitable domestic sheep grazing range. The area of mapped
overlap is heavily forested with dense mature forest with few rock outcrops and provides
little suitable habitat for bighorn sheep, and little suitable forage for domestic sheep. For
these reasons, domestic sheep would pass rapidly from their drop off point through the
narrow zone of overlap to the nearest grazing areas to the north of the zone of overlap.
The habitats in this portion of the allotment are consistent with the description provided
by Schommer and Woolever (2001) of a continuous forest that could serve as a natural
barrier to bighorn sheep movement. The area has few rock outcrops or other structures
that provide typical bighorn sheep escape cover. It is about 3.5 air miles from the rim of
the Animas River canyon to the nearest suitable domestic sheep grazing area. There have
been no recent Bighorn sheep sightings in the mapped overlap area. This allotment has
been vacant since 1989.
This allotment is proposed to be placed into forage reserve status. When active however,
all of the project design criteria and adaptive management practices for active allotments
would be applied to this allotment. We anticipate this allotment may be used once per 15
years in an emergency situation, such as the Missionary Ridge fire of 2002.
Summary of Risk Rating for Flume Allotment:
Risk Rating: Alternative 2 – Low
Alternative 3 – Low
Under Alternative 2, if the Flume Allotment were to be restocked, the lack of suitable
habitat for domestic sheep or bighorn sheep in or near the zone of overlap, and the
distance from the Animas River canyon (about 3.5 miles) results in a rating of “Low Risk”
for contact. If the allotment were to remain vacant under Alternative 2, the rating would
be “Low Risk” because domestic sheep would not be permitted in the allotment and there
would be a low risk for contact.
Under Alternative 3, the Flume Allotment would be managed as a forage reserve allotment
and grazed by domestic sheep only on an irregular basis. Project design criteria would be
applied to the allotment when it was active, and the habitat conditions described above
would all result in a rating of “Low Risk” for contact.
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