Picea sitchensis

Picea sitchensis, commonly called the Sitka spruce, is a massive evergreen conifer native to North America's west coast. It gets its name from Sitka, a town in southeast Alaska where the tree is common.

This is the largest spruce species by far and ranks as the fifth-largest conifer globally, behind giant sequoia, coast redwood, kauri, and western redcedar. It is also the third-tallest tree species, after coast redwood and South Tibetan cypress, and one of only three species known to exceed 100 meters (330 feet) in height. Its range hugs the western coast of Canada and the United States, extending south into northern California.

The bark is thin and scaly, flaking off in small, circular plates 5–20 centimeters across, with a reddish-brown inner layer. Young trees have a broad, cone-shaped crown that becomes cylindrical with age; older trees often have no branches below 30–40 meters. The shoots are very pale buff-brown, nearly white, hairless, and have prominent pulvini. The needle-like leaves are stiff, sharp, 15–25 millimeters long, flattened, dark glaucous blue-green above with two or three thin lines of stomata, and blue-white below with two dense bands of stomata.

Cones are pendulous, slender, and cylindrical, 6–10 cm long and about 2 cm wide when closed, opening to 3 cm wide. Their thin, flexible scales are 15–20 mm long, and the bracts just above them are the longest of any spruce, sometimes slightly visible on closed cones. Cones are green or reddish, maturing to pale brown 5–7 months after pollination. Seeds are black, 3 mm long, with a slender, pale brown wing 7–9 mm long.

More than a century of logging has left only remnants of the original spruce forest, and the largest trees were cut before careful measurements could be made. Trees over 90 meters tall still exist in Pacific Rim National Park and Carmanah Walbran Provincial Park on Vancouver Island (the Carmanah Giant, at 96 meters, is Canada's tallest tree), as well as in Olympic National Park, Washington, and Redwood National Park, California. The tallest known individual, at 100.2 meters, grows in Redwood National Park; two others there are just over 96 meters. The largest Sitka spruce by trunk volume is the Queets Spruce in Olympic National Park, with a volume of 346 cubic meters, a height of 74.6 meters, and a diameter at breast height of 4.4 meters. Another large specimen at Klootchy Creek Park, Oregon, had a circumference of 15 meters and a height of 66 meters.

Sitka spruce is long-lived, with the oldest known individual just under 600 years old. Because it grows rapidly in good conditions, large size does not necessarily mean great age. The Queets Spruce is estimated to be only 350 to 450 years old but adds more than a cubic meter of wood each year.

The tree has a shallow root system with long lateral roots and few branches, an adaptation to extremely wet, poorly drained soil. This makes it susceptible to wind throw.

In the Olympic National Forest in Washington, Sitka spruce trees near the ocean sometimes develop burls. According to a guidebook, damage to the tip or bud causes growth cells to divide more rapidly, forming the swelling. Burls do not affect overall tree growth.

DNA analysis shows that only Picea breweriana has a more basal position than Sitka spruce among spruces. The other 33 spruce species are more derived, suggesting that the genus Picea originated in North America.

Sitka spruce is native to the west coast of North America, from the Kenai Peninsula in Alaska south to near Fort Bragg in northern California. It is closely tied to temperate rainforests and, in the southern part of its range, is found within a few kilometers of the coast. North of Oregon, it extends inland along river floodplains but rarely more than about 80 kilometers from the Pacific Ocean and its inlets. In Alaska, it grows up to about 2,500 meters above sea level; farther south, it is generally below 450 meters. Forests containing Sitka spruce average 200 to 500 centimeters of rain annually. The tree tolerates salty spray common in coastal dune habitats, such as at Cape Disappointment State Park in Washington, and prefers soils high in magnesium, calcium, and phosphorus.

Introduced to Europe as a lumber tree in the 19th century, Sitka spruce plantations now dominate forests in Great Britain (25% of forest cover) and Ireland (52%). It is also present in France and Denmark, and was introduced to Iceland and Norway in the early 20th century. Along the Norwegian coast, Sitka spruce grows 25–100% faster than native Norway spruce, even as far north as Vesterålen, and the fastest-growing plantations in Europe are on Norway's southwest coast. A 9-meter-tall, 100-year-old Sitka spruce growing on uninhabited sub-antarctic Campbell Island is recognized by Guinness World Records as the most remote tree in the world.

Sitka spruce provides critical habitat for a wide variety of mammals, birds, and reptiles.