Effects on Vegetation near the Stibnite Mining Project

Overall, the 2021 Mine Management Plan (MMP)-related vegetation clearing would impact 3,564 acres, including primarily undisturbed areas for the Burntlog Route where an increase in the potential for non-native plant establishment and spread would be more deleterious. The Johnson Creek Route Alternative would impact 3,399 acres through vegetation clearing; however, much of the disturbance area would be along or near previously disturbed areas (i.e., existing roads) where non-native plants are already established or could become established as a result of previously authorized activities.

The 2021 MMP would remove an estimated 259.5 acres of occupied whitebark pine habitat and 78 acres of assumed occupied habitat (16.3% of occupied habitat in the analysis area) and 287.4 acres of modeled suitable habitat (6.7% of modeled suitable habitat in the analysis area), totaling 1,278 trees (27 would be individuals observed with cones during 2019 field surveys). Impacts to the whitebark pine would be less under the Johnson Creek Route Alternative as an estimated 108.5 acres of occupied whitebark pine habitat and 78 acres of assumed occupied habitat (9.0% of occupied habitat in the analysis area) but no additional acres of modeled suitable habitat, totaling an estimated 777 trees (27 would be individuals observed with cones during 2019 field surveys) would be removed. The mine site and access roads would remove the majority of whitebark pine individuals and habitat, while impacts as a result of the utilities and off-site facilities would be minimal. Indirect impacts to occupied whitebark pine habitat may occur during implementation of the 2021 MMP and Johnson Creek Route Alternative, primarily as a result of dust, impacts to seed dispersers (e.g., Clark’s nutcracker), and increased erosion and sedimentation where disturbance occurs. These indirect impacts would occur near all Project components but especially along the access roads and utilities as this species has been documented over a large area in the vegetation analysis area and surveyed occupied habitat totals approximately 2,069 acres.

The Project would result primarily in localized, long-term and permanent, moderate impacts to the whitebark pine. The 2021 MMP would impact known occurrences of bent-flowered milkvetch, least moonwort, Sacajawea’s bitterroot, Blandow’s helodium, sweetgrass, and Rannoch-rush, while the Johnson Creek Route Alternative would impact known occurrences of bent-flowered milkvetch, least moonwort, and Sacajawea’s bitterroot. Additionally, the 2021 MMP would impact a greater amount of modeled potential habitat for sensitive and forest watch plant species than the Johnson Creek Route Alternative. Impacts as a result of increased potential for non-native plant establishment and spread may be regional in nature due to the relatively large amount of habitat disturbance associated with the 2021 MMP and Johnson Creek Route Alternative ¹ .