DOE/EIS-0332; McNary-John Day Transmission Line Project Draft ...

BPA McNary-John Day Transmission Project
Draft EIS
February 2002
Vegetation
Fire damage in lithosol vegetation communities could result in expansion of nonvegetated,
bare rock areas. The shallow soils over bedrock in these communities are
stabilized by vegetation. Loss of the vegetation could lead to the loss of soils in some
areas.
Fire in the cottonweed plantation would result in losses of trees. Replacement of mature,
harvestable trees would take 7 to 10 years. Fire loss of trees in hedgerows and isolated
patches elsewhere on the alignment would take longer to replace. Tree species identified
on the right-of-way would take approximately 25 years to regenerate to mature
individuals.
Impact acreage from access road operation would be highest in the grazed shrub-steppe
cover type. Ten acres of this cover type would be converted to roadbed. Many of the
existing two-track roadbeds in this cover type, and throughout the route, are dominated
by low cheatgrass. As such they have a close affinity to the surrounding degraded shrubsteppe,
even while converted to access roads. Impact acreage within higher quality
vegetation communities (such as shrub-dominated shrub-steppe) are lower, but would
result in the creation of new edge communities and a permanent avenue of invasion for
nonnative and/or disturbance-favored species.
Tower Operation and Maintenance
The proposed line would require the placement of 360 steel lattice towers. Each tower
would take up approximately 0.05 acre. Of the towers to be placed, approximately 144
would be placed in grazed shrub-steppe vegetative cover, 118 would be placed in
agricultural cover, 75 would be in grasslands, 26 would be in scabland/lithosol
communities, and 11 would be in shrub-dominated shrub-steppe cover. No towers would
be placed in riparian communities. Acreages permanently impacted by tower placement
are presented in Table 3-12.
Tower operation is regarded as a permanent impact to vegetation communities, because it
requires the removal and displacement of existing vegetation and results in the
compaction of soils. However, the grassland and grazed shrub-steppe communities
would likely return to and recover at least some of the area beneath the towers within 1 to
5 years of construction. Shrub-dominated shrub-steppe and scabland/lithosol
communities may also return to portions of the areas under towers, but over a longer time
period, and with more intensive management. Based on conditions observed at existing
towers, it is likely that a combination of native and nonnative species would establish
around the towers. Nonnatives commonly observed around towers include cheatgrass,
medusa-head wild rye, and bulbous bluegrass. Native species seen around existing
towers include bluebunch wheatgrass, big sagebrush, and gray rabbitbrush. Agricultural
cover types would not return to the areas under new towers.
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