Pseudotsuga Menziesii - Ecology

Ecology

The rooting habit of coast Douglas-fir is not particularly deep, with the roots tending to be shallower than those of same-aged Ponderosa Pine, Sugar Pine, or California Incense-cedar, though deeper than Sitka Spruce. Some roots are commonly found in organic soil layers or near the mineral soil surface. However, Douglas-fir exhibits considerable morphological plasticity, and on drier sites coast Douglas-fir will generate deeper taproots. Interior Douglas-fir exhibits even greater plasticity, occurring in stands of interior temperate rainforest in British Columbia, as well as at the edge of semi-arid sagebrush steppe throughout much of its range, where it generates even deeper taproots than coast Douglas-fir is capable.

Douglas-fir snags are abundant in forests older than 100–150 years and provide cavity-nesting habitat for numerous forest birds. Mature or "old-growth" 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 (4 square kilometres (990 acres) of old-growth. Red tree voles may also be found in immature forests if Douglas-fir is a significant component. This animal nests almost exclusively in the foliage of Douglas-fir trees. Nests are located 2–50 metres (6.6–160 ft) above the ground. The red vole's diet consists chiefly of Common Douglas-fir needles. A parasitic plant sometimes utilizing P. menziesii is Douglas-fir Dwarf Mistletoe (Arceuthobium douglasii).

Its seedlings are not a preferred browse of Black-tailed Deer (Odocoileus hemionus columbianus) and elk (Cervus canadensis), but can be an important food source for these animals during the winter when other preferred forages are lacking. In many areas, coast Douglas-fir needles are a staple in the spring diet of blue grouse (Dendragapus). In the winter, New World porcupines primarily eat the inner bark of young conifers, among which they prefer Douglas-fir.

The leaves are also used by the woolly conifer aphid Adelges cooleyi; this 0.5 mm long sap-sucking insect is conspicuous on the undersides of the leaves by the small white "fluff spots" of protective wax that it produces. It is often present in large numbers, and can cause the foliage to turn yellowish from the damage in causes. Exceptionally, trees may be partially defoliated by it, but the damage is rarely this severe. Among Lepidoptera, apart from some that feed on Pseudotsuga in general (see there) the gelechiid moths Chionodes abella and C. periculella as well as the cone scale-eating tortrix moth Cydia illutana have been recorded specifically on P. menziesii.

Douglas-fir seeds are an extremely important food for small mammals. Mice, voles, shrews, and chipmunks consumed an estimated 65 percent of a Douglas-fir seed crop following dispersal in western Oregon. The Douglas Squirrel (Tamiasciurus douglasii) harvests and caches great quantities of Douglas-fir cones for later use. They also eat mature pollen cones, developing inner bark, terminal shoots, and tender young needles. The seeds are also important in the diets of several seed-eating birds. These include most importantly American sparrows (Emberizidae) – Dark-eyed Junco (Junco hyemalis), Song Sparrow (Melospiza melodia), Golden-crowned Sparrow (Zonotrichia atricapilla) and White-crowned Sparrow (Z. leucophrys) – and true finches (Fringillidae) – Pine Siskin (Carduelis pinus), Purple Finch ("Carpodacus" purpureus), and the Douglas-fir Red Crossbill (Loxia curvirostra neogaea) which is uniquely adapted to foraging for P. menziesii seeds.

The coast Douglas-fir variety is the dominant tree west of the Cascade Mountains in the Pacific Northwest, occurring in nearly all forest types, competes well on most parent materials, aspects, and slopes. Adapted to a moist, mild climate, it grows larger and faster than Rocky Mountain Douglas-fir. Associated trees include Western Hemlock, Sitka Spruce, Sugar Pine, Western White Pine, Ponderosa Pine, Grand Fir, Coast Redwood, Western Redcedar, California Incense-cedar, Lawson's Cypress, Tanoak, Bigleaf Maple and several others. Pure stands are also common, particularly north of the Umpqua River in Oregon.

Shrub associates in the central and northern part of Coast Douglas-fir's range include Vine Maple (Acer circinatum), Salal (Gaultheria shallon), Pacific Rhododendron (Rhododendron macrophyllum), Oregon-grape (Mahonia aquifolium), Red huckleberry (Vaccinium parvifolium), and Salmonberry (Rubus spectabilis). In the drier, southern portion of its range shrub associates include California Hazel (Corylus cornuta var. californica), Oceanspray (Holodiscus discolor), Creeping Snowberry (Symphoricarpos mollis), Western Poison-oak (Toxicodendron diversilobum), Ceanothus (Ceanothus spp.), and Manzanita (Arctospaphylos spp.). In wet coastal forests, nearly every surface of old-growth Coast Douglas-fir is covered by epiphytic mosses and lichens.