Picea engelmannii

Picea engelmannii, called Engelmann spruce, mountain spruce, or silver spruce, grows in western North America. It is valued for its wood, which makes excellent tone wood for acoustic guitars and other instruments. This tree is mostly found at high elevations in mountains, but also appears in cool, watered canyons.

The tree reaches 25–40 meters tall, sometimes up to 65 meters, with a trunk up to 1.5 meters across. Its reddish bark is thin and scaly, flaking in small circular plates 5–10 centimeters wide. Young trees have a narrow cone-shaped crown that becomes cylindrical with age. Shoots are buff-brown to orange-brown, usually densely hairy, with prominent pulvini. Needles are 15–30 millimeters long, flexible, rhombic in cross-section, glaucous blue-green above with thin stomatal lines, and blue-white below with two broad stomatal bands. Crushed needles have a pungent odor.

In spring, purple cones about 1 centimeter long release yellow pollen when windy. The pendulous, slender cylindrical cones are 2.5–8 centimeters long, 1.5 centimeters wide when closed, opening to 3 centimeters wide. Their thin, flexible scales are 1.5–2 centimeters long with wavy margins. Cones are reddish to dark purple, maturing to light brown 4–7 months after pollination. Seeds are black, 2–3 millimeters long, with a slender, light brown wing 5–8 millimeters long. At the alpine tundra fringe, the tree grows in a krummholz form.

Engelmann spruce grows from 520 to 3,650 meters above sea level, rarely lower in the northwest. It is common in the Rocky Mountains and east slopes of the Cascade Range from central British Columbia to southern Oregon, and in Montana, Idaho, and Colorado, with sparser populations toward Arizona and New Mexico in the Sky Islands. Two isolated populations occur in northern Mexico. It appears in Idaho Panhandle canyons and, more limitedly, in the northeastern Olympic Mountains, where some exceptionally large specimens exist—one 2.1 meters in diameter and 55 meters tall. In the Cascades, it grows mostly on eastern slopes from 900–1,800 meters, and liberally in the Rocky Mountains. It also occurs in the Monashee and Selkirk Mountains and highlands around the Interior Plateau.

Small saplings reduce transpiration when buried in snowpack. Loss of snowpack increases transpiration, and with low sapwood water reserves and extended soil frost in windswept areas, this may prevent regeneration above and below the tree line. Water uptake and root-stored water are critical for saplings exposed above snowpack from late winter to early spring. For exposed trees, soil water availability may be critical in late winter when transpirational demands rise. Cuticular damage from windblown ice is more important at the tree line, while desiccation damage is more important at lower elevations. Despite wind damage, Engelmann spruce tends to grow taller than other trees at the tree line. It is shade tolerant but less so than subalpine fir, so it depends somewhat on fires to outgrow competitors, though its thin bark and shallow roots make it fire-vulnerable. Spruce bark beetles attack it, especially deadly to centuries-old stands. It is also susceptible to avalanches. Older spruce forests offer little forage for animals, but after fires they often burn completely, allowing many other plants, especially deciduous ones, to rise. Streams shaded by Engelmann spruce are used by trout, and aphids produce galls that hang from the tree, resembling dried cones.

Two geographical subspecies are accepted: *Picea engelmannii* subsp. *engelmannii* (Engelmann spruce) covers most of the range; *Picea engelmannii* subsp. *mexicana* (Mexican spruce) occurs in two isolated populations in northern Mexico—on the Sierra del Carmen in Coahuila and on Cerro Mohinora in Chihuahua—and possibly in the Madrean sky islands of southeast Arizona and southwest New Mexico, though this is disputed. Engelmann spruce hybridizes extensively with white spruce (forming *Picea × albertiana*, Alberta spruce or interior spruce) in interior Canada, and to a lesser extent with Sitka spruce where they meet on the western fringes of the Cascades.

Native Americans made medicines from its resin and foliage. Its wood is light and fairly strong, harvested for paper-making and general construction. Slow-grown wood from high elevations is especially prized for soundboards of acoustic guitars, harps, violins, and pianos. Because it is odorless and low in resin, it has been used for food containers like barrels. It is also used to a small extent as a Christmas tree.