Douglas fir Douglas-fir forest is the primary habitat of the red tree vole ("Arborimus longicaudus") and the spotted owl ("Strix occidentalis"). Home range requirements for breeding pairs of spotted owls are at least 400 ha () of old growth. Red tree voles may also be found in immature forests if Douglas-fir is a significant component. The red vole nests almost exclusively in the foliage of the trees, typically above the ground, and its diet consists chiefly of Douglas-fir needles. A parasitic plant sometimes utilizing "P. menziesii" is Douglas-fir dwarf mistletoe ("Arceuthobium douglasii"). The leaves are also used by the woolly conifer aphid
Douglas Ranges flows along the southeast flank of the range. East of the Douglas Ranges, across Harrison Lake, are the Lillooet Ranges, while to the west and northwest are the Garibaldi Ranges. Southeast across the Fraser River is the Canadian portion of the Cascade Range. Because of the warmer climate (relative to the rest, even, of the British Columbia coastal lowlands), there were forests of immense trees throughout the Douglas Ranges, which were logged relatively early on in British Columbia's history. A network of logging railroads ran throughout the basin of the Chehalis River, which drains the core of the ranges to