Western yew

Western yew (Tw) - Taxus brevifolia

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Geographic range and ecological amplitudes 

Description

Pacific yew varies in size from a shrub to small-sized (<20m tall) evergreen gymnosperm, with an irregular crown, long branches, twisted and fluted stem, and scaly bark at maturity. The wood is hard and heavy, and resistant to decay. The bark was used in cancer research as it yields the taxol, a key component of cancer-fighting drug, tamoxifen. Demand for yew bark increased dramatically until it was possible to synthesize taxol chemically.

Geographic range 

Geographic element:
Western North American/Pacific and Cordilleran

Distribution in Western North America:
(north), central, and south in the Pacific region; central and south in the Cordilleran region

Ecological amplitudes 

Climatic amplitude:

subalpine boreal - cool temperate - cool mesothermal

Orographic amplitude:

submontane - montane - (subalpine)

Occurrence in biogeoclimatic zones:
(lower MH), (lower ESSF), (MS), IDF, ICH, CDF, CWH

Edaphic amplitude

Western (Pacific) yew

Range of soil moisture regimes:
(very dry) - moderately dry - slightly dry - fresh - moist - very moist - (wet)

Range of soil nutrient regimes:
(very poor) - poor - medium - rich - very rich

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Tolerances and damaging agents

Root system characteristics

Pacific yew develops a deep and wide spreading root system. Roots are associated with vesicular-arbuscular mycorrhizae.

Tolerances
Tolerance to Tolerance class Comments
low light H considered as our most shade-tolerant gymnosperm
frost M  
heat M frequent on warm and dry sites (for example, in CDF)
water deficit M frequent on dry and warm sites (for example, in CDF)
water surplus H infrequent on wet sites
nutrient (mainly N) deficiency H infrequent in acid, poor soils

Associated tree species and successional role

In British Columbia, Pacific yew grows scattered in isolated clumps of one or several individuals (very rarely it forms a pure stand) in the understory of conifers, such as Pacific silver fir, Grand firs, Red alder, Western larch, Ponderosa pine, Black cottonwood, Common douglas, Western redcedar, and Western hemlock. Pacific yew is present in early, mid-, and late stages of secondary succession.

Silvical characteristics
Characteristic Interpretive class Comments
reproduction capacity M a prolific seed producer, but the frequency of seed crops is unknown
seed dissemination capacity H seed is dispersed mainly by birds, rodents, and squirrels
potential for natural regeneration in low light H high, if considering vegetative reproduction
potential for natural regeneration in the open H except in situations where it is protection-requiring
potential initial growth rate (<5 years) M about 20cm/yr in planted seedlings
response of advance regeneration to release na not determined
self-pruning capacity in dense stands na dense stands are non-existent
crown spatial requirements H long branches and wide, umbrella-shaped, live-crown
light conditions beneath closed-canopy, mature stands na closed-canopy stands are non-existent
potential productivity na non-crop species; site index functions are not available
longevity ? not determined

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Genetics and notes

Genetics

Pacific yew was originally classified as a variety of European yew — Taxus baccata. Where different species of yew grow near each other, interspecific hybrids frequently occur, lending support to the view that there is but one species of the seven currently recognized Taxus species.

Notes

Although not a timber species, Pacific yew has several special uses — the most important one for medicinal purposes. It would be feasible to grow Pacific yew for bark production under intensive silviculture management on suitable sites. More detailed silvics information is given by:

Bolsinger, C.L. and A.E. Jaramillo. 1990. Taxus brevifolia. Pp. 573-579 in R.M. Burns and B.H. Honkala (technical coordinators) Silvics of North America, Vol. 1. Agri. Handbook 654, USDA For. Serv., Washington, D.C.

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