Native to the Pacific coast of North America and introduced in 1831 from seed collected by David Douglas (1799-1834), Sitka Spruce was first valued and planted as an elegant ornamental. Its productivity soon became clear, and it became the principal commercial timber species in twentieth-century afforestation of the British and Irish uplands.
Its native range is a narrow strip along North America’s west coast, the ‘Pacific fog belt’, stretching 2,900km from Alaska to California. It grows with White Spruce and subalpine conifers in the north, and with Western Hemlock, Douglas-fir, Lawson’s Cypress, Shore Pine, Western Red Cedar and Giant Redwood further south. In Britain and Ireland it grows almost anywhere but is less frequent in the south-east.
At home in wet, humid, harsh places, it naturally grows in mixtures. Monoecious, producing cones from at least 30 years old, with female cones usually near the treetop on primary branches and male cones lower on older branches. Cones mature in one year.
One of our largest trees, to 60m, with a long leader. Its sharp, spiny, dark green needles are straight with a flattened diamond cross-section and two bright bands beneath. Cones hang below branches, to 10cm. Bark purple-grey with scaly plates. Norway Spruce differs: red-brown bark, slightly curved square-sectioned needles, cones to 20cm.
Best in the wet uplands of Britain and Ireland with over 1,000mm rainfall, staying uncommon in mainland Europe. Tolerant of salt coastal winds. For timber, clones of suitable provenances are advised, usually from Washington state, as more northerly Alaskan ones grow too slowly. Branches are very dense, so unbrashed plantations become impenetrable.
Its poor environmental reputation in Britain and Ireland is unjust. Early afforestation used large monocultures, often badly sited, ignoring landscape, wildlife and archaeology. Modern forestry is far more sensitive and alert to the risks of low diversity in species, age and structure. Research has found over 500 wildlife species using Sitka Spruce, and mixed plantations would enhance this further.
Susceptible to decay when injured by root-rotting pathogens. In plantations, fast growth gives poor root systems, raising windthrow risk on waterlogged, exposed sites. Threatened by the Eight-toothed Spruce Bark Beetle (Ips typographus). A warming climate will narrow its European range, bringing drought stress in the south and east but potentially greater productivity in the west.
Valued more for timber yield than quality, which is inferior to Norway Spruce. Rapid growth gives lightweight, non-resinous, fairly low-strength wood, well suited to woodpulp, its long fibres making high-quality paper. Strength grading qualifies it for general construction, where low stiffness from rapid growth usually limits its use.
