glauca,[3] but genetic[4] and morphological[5] evidence suggest that Mexican populations should be considered a different variety (Pseudotsuga menziesii var.

[9] The strong ecological and genetic differentiation with intergradation limited primarily to postglacial contact zones in British Columbia[10][11] supports infraspecific groupings.

Some botanists have further split Rocky Mountain Douglas-fir into two varieties,[12] but these are not widely acknowledged and have only limited support from genetic testing.

Fine-root production is episodic in response to changing environmental conditions; the average lifespan of fine roots is usually between several days and several weeks.

This longevity is apparently uncommon; growing on a relatively barren lava field has protected it from fire, animals, and humans.

In the dry-belt forests of central British Columbia, ages can exceed 500 years on sites normal for the region.

The oldest accurately-dated growth ring available for the region is 1475; dates in the 1500s and 1600s are more common for remnant patches that have escaped logging, fire, and other disturbances.

It is affected by the diseases Phaeolus schweinitzii, Armillaria, Phellinus weirii, Fomes annosus, dwarf mistletoe, Dasyscypha canker and Rhabdocline needle cast.

In spring and winter (in British Columbia, Idaho, and Montana) elk browse on south- and southwest-facing Rocky Mountain Douglas-fir and ponderosa pine stands, particularly when shrubs and/or grasses are productive.

In summer, elk generally are found at higher elevations (outside the Rocky Mountain Douglas-fir and Pacific ponderosa pine zones).

Chipmunks, mice, voles, and shrews eat large quantities of conifer seeds from the forest floor, and clipped cones are a staple and major part of storage of red squirrels.

Blue grouse forage on needles and buds in winter; they and other birds rely heavily on Rocky Mountain Douglas-fir communities for cover.

The Douglas-fir is vulnerable to infestation by a woolly aphid, Adelges cooleyi that also infects the Engelmann spruce to complete its lifecycle.

Other uses listed include "machine-stress-rated lumber", glued-laminated (Glulam) beams, pallets, furniture, cabinets, doors, flooring, window frames, and other miscellaneous woodwork and millwork.