Western hemlock (WH)

Tsuga heterophylla

Native range

Native to the Pacific north-west of America with a wide range from Alaska to California.

Provenance choice

Provenances from Vancouver Island are recommended, although more southerly origins could be used on sheltered sites with low frost risk.

Site requirements

A shade tolerant species best suited to moister climates in Britain with >1000 mm rainfall. It has rapid growth and high volume production on suitable sites and regenerates freely in a wide range of upland forests. It is cold hardy throughout Britain, but is very sensitive to late frosts, does not tolerate exposure and is drought sensitive. As a consequence trees are often of poor form (e.g. multi-stemmed). These factors mean that it should not be used for afforestation of open ground, but it can be planted under light shade. Although it suffers from heather competition, it will grow on soils of very poor to medium nutrient status and of slightly dry to moist soil moisture. Not suited to peats or very dry soils. Best growth will be found on acid brown earths on lower valley sides in upland forests. Can grow in mixture with other conifers such as Sitka spruce and Douglas fir.

Pests and pathogens

Largely free of major pathogens, western hemlock is nonetheless considered highly susceptible to Heterobasidion (Fomes root and butt rot).

Use

Although currently a minor species, its high regeneration capacity means that it is likely to persist in many upland forests.