Pacific yew is a slow-growing evergreen shrub or tree which commonly reaches 20 to 40 feet at maturity. On favorable coastal lowland sites, scattered individuals can grow to 60 feet in height and have diameters of 2 to 3 feet or more. On poor sites, such as those at higher elevations, Pacific yew grows as a large sprawling shrub. This large shrub or tree can reach maturity at 250 to 350 years of age and often survives for several centuries. Pacific yew is characterized by a conical crown and slender, drooping horizontal branchlets. The trunk is limby and often contorted or malformed. Twigs are slender, hairless and green, but become dark reddish brown in the second growing season. Bark is very thin (approximately 0.25 inch, scaly, with purplish outer scales covering newly formed reddish or purplish inner bark. The root system is fibrous. The sharp-pointed leaves are linear to lanceolate, 0.5 to 1 inch long, and spirally arranged. Leaves are dark yellow-green above and paler beneath. Leaves persist for at least 5 to 6 years. Pacific yew is dioecious.. Globose, yellowish staminate cones approximately 0.12 inch in length are produced in abundance on male plants. Single, greenish, ovulate cones are borne on the lower sides of branches. Fruit is a red, fleshy, ovoid, berrylike aril. Each fruit is approximately 0.4 inch in length and matures in one season. The cup-shaped fruit surrounds a large single, naked seed. The seed is reddish, obvoid-oblong, with a hard bony shell exposed at the apex.
The Pacific yew grows in a variety of cool and moist shaded habitats in coastal lowlands and mountains. It occurs in canyon bottoms, on moist forested flats near streams, and scattered at various upland sites. At middle elevations in northern Idaho, it forms a dense tangle of shrubs approximately 10 to 15 feet in height. Elsewhere, small groups or scattered individuals are more common. In the northern Rockies, it is associated with grand fir and western red cedar forests The pacific yew grows in cool temperate climates. Abundance increases with increasing precipitation and decreases with greater elevation and latitude. Average annual precipitation ranges from 18 to 116 inches.. Sites are generally characterized by mild wet winters and warm dry summers. Pacific yew is moderately tolerant of frost, but the protection offered by a layer of snow is necessary in continental climates. This plant is resistant to flooding and survives temporary inundation. Soils: Western yew commonly grows on deep, moist, well-drained soils and is well adapted to acidic conditions. In the Bitterroot Mountains of Montana and Idaho indicated that sites dominated by Pacific yew have high levels of nitrogen. Pacific yew grows at elevations ranging from 2,000 to 8,000 feet.
Pacific yew is present in many climax or near climax communities of the Pacific Northwest and northern Rocky Mountains. It is a particularly common component of old-growth grand fir, western red cedar, and Douglas-fir-western hemlock communities. Pacific yew increases in cover up to a stand age of at least 500 years in northwestern old growth Douglas-fir forests which are characterized by long fire-free intervals. This fire-sensitive species is absent from areas characterized by high fire frequencies. Pacific yew does occur on disturbed sites, including previously logged stands, but reaches greatest abundance in undisturbed areas. Plants often grow as suppressed individuals in undisturbed stands. Pacific yew was common in mature stands 230 years or older but was absent in second-growth communities. Found in old-growth forests in canyons of the Bitterroot Mountains in Idaho and Montana are commonly dominated by Pacific yew, western red cedar, and/or grand fir. (Source)