Editing Douglas fir (section)

==Ecology==

=== Preferred sites ===
Douglas-fir prefers acidic or neutral soils, such as [[Olympic (soil)|Olympic soil]].<ref>{{cite web |url=https://www.arborday.org/trees/treeguide/treedetail.cfm?itemID=836 |title=Douglas-fir Tree on the Tree Guide|work=arborday.org}}</ref> However, it exhibits considerable morphological plasticity, and on drier sites ''P. menziesii'' var. ''menziesii'' will generate deeper taproots. ''Pseudotsuga menziesii'' var. ''glauca'' 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 still.

The coast Douglas-fir variety is the dominant tree west of the Cascade Mountains in the [[Pacific Northwest]]. It occurs in nearly all forest types and competes well on most parent materials, aspects, and slopes. Adapted to a more moist, mild climate than the interior subspecies, 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]], [[incense-cedar|California incense-cedar]], [[Chamaecyparis lawsoniana|Lawson's cypress]], [[tanoak]], [[bigleaf maple]] and several others. Pure stands are also common, particularly north of the [[Umpqua River]] in Oregon. It is most dominant in areas with a more frequent fire regime that suppresses less fire-resistant conifers.<ref name=":1" />

=== Use by animals ===
[[File:Pseudotsuga menziesii 01221.JPG|thumb|upright=.85|A [[snag (ecology)|snag]] provides nest cavities for birds.]]

Douglas-fir seeds are an extremely important food source for small mammals such as [[Mole (animal)|moles]], [[shrew]]s, and [[chipmunk]]s, which consume an estimated 65% of each annual seed crop. The [[Douglas squirrel]] harvests and hoards great quantities of Douglas-fir cones, and also consumes mature pollen cones, the inner bark, terminal shoots, and developing young needles.<ref name=":0" />

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 {{convert|400|ha|km2 acre}} 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 {{convert|2|-|50|m|ft|round=5}} above the ground, and its diet consists chiefly of Douglas-fir needles.<ref name=":0" />

Douglas-fir needles are generally poor [[Browsing (herbivory)|browse]] for [[ungulate]]s, although in the winter when other food sources are lacking it can become important, and [[black-tailed deer]] browse new seedlings and saplings in spring and summer. The spring diet of the [[Dendragapus|blue grouse]] features Douglas-fir needles prominently.<ref name=":0" />

The leaves are also used by the [[Adelgidae|woolly conifer aphid]] ''[[Adelges cooleyi]]''; this 0.5&nbsp;mm-long [[Sap (plant)|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 it 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, the [[gelechiid moth]]s ''Chionodes abella'' and ''C.&nbsp;periculella'' as well as the cone scale-eating [[tortrix moth]] ''[[Cydia illutana]]'' have been recorded specifically on ''P.&nbsp;menziesii''.

The inner bark is the primary winter food for the [[North American porcupine]].<ref name=":0" />

[[Poriol]] is a flavanone, a type of flavonoid, produced by ''P. menziesii'' in reaction to infection by ''[[Poria weirii]]''.<ref>{{cite journal|author=Barton GM|year=1972|title=New C-methylflavanones from Douglas-fir|journal=Phytochemistry|volume=11|issue=1|pages=426–429|doi=10.1016/S0031-9422(00)90036-0|bibcode=1972PChem..11..426B }}</ref>

=== Value to other plants ===
A [[parasitic plant]] which uses ''P. menziesii'' is the [[Douglas-fir dwarf mistletoe]] (''Arceuthobium douglasii''). [[Epiphyte]]s such as [[crustose lichen]]s and mosses are common sights on Douglas-firs.<ref name=":1" /> As it is only moderately [[shade tolerant]],<ref name=":02" /> undisturbed Douglas-fir stands in humid areas will eventually give way to later successional, more shade-tolerant associates such as the western redcedar and western hemlock—though this process may take a thousand years or more.<ref name=":0" /> It is more shade tolerant than some associated fire-dependent species, such as [[western larch]] and ponderosa pine, and often replaces these species further inland.<ref name=":02" />

=== Diseases and insects ===
Fungal diseases such as [[laminated root rot]] and [[Armillaria mellea|shoestring root-rot]] can cause significant damage, and in plantation settings dominated by Douglas-fir monocultures may cause extreme damage to vast swathes of trees.<ref name=":0" /> Interplanting with resistant or nonhost species such as western redcedar and [[Corylus cornuta|beaked hazelnut]]<ref>{{Cite web|title=Corylus cornuta|url=https://www.fs.fed.us/database/feis/plants/shrub/corcor/all.html|access-date=2021-05-12|website=www.fs.fed.us}}</ref> can reduce this risk. Other threats to Douglas-fir include [[Phellinus pini|red ring rot]] and the [[Dendroctonus pseudotsugae|Douglas-fir beetle]].<ref name=":0" />