The Ponderosa Pine zone generally
forms open stands often associated with bluebunch wheatgrass and
other species typical of the Bunchgrass zone. In the Columbia Basin,
this zone occupies a narrow band along the valley bottom and lower
side- walls of the valley near Cranbrook and around Lake Koocanusa.
Outside the basin it occurs only in major river valleys of the Fraser
(Lytton-Lillooet area), lower Thompson, Nicola, Similkameen and
lower Kettle. The vegetation is a mosaic of forest and grassland,
with a ponderosa pine canopy and an understory of bluebunch wheatgrass,
rough fescue, and arrow-leafed balsamroot. Other species include
pasture sage, lemonweed, rosy pussytoes, orange arnica, silky lupine,
junegrass, cheatgrass, Idaho fescue and yarrow. Due to its location
in the valley bottom and near an urban area, the Ponderosa Pine
zone is one of the most threatened plant communities in the Columbia
Basin.
