Alaska is home to roughly a dozen native tree species, split between the dense temperate rainforests of the southeast coast and the vast boreal forests of the interior. The state divides into four major vegetation zones: coastal forest, boreal forest (also called taiga), lowland tundra, and upland tundra. Trees dominate the first two zones, while the tundra regions of the Arctic, northwest, southwest, and Aleutian Islands are largely treeless.
Coastal Rainforest Trees of Southeast Alaska
The panhandle of southeast Alaska supports a lush temperate rainforest dominated by evergreens. Sitka spruce and western hemlock form the backbone of this forest, with Sitka spruce earning the distinction of Alaska’s official state tree in 1962. Mature Sitka spruce near sea level can exceed 200 feet in height and 10 feet in trunk diameter, and individual trees may live 700 to 800 years. On average sites in southeast Alaska, a Sitka spruce can reach about 90 feet within 50 years.
Western hemlock thrives in the same wet, mild conditions and is one of the most shade-tolerant trees in the region. Mountain hemlock, its higher-elevation relative, grows in areas with cool to cold maritime climates, short growing seasons, and heavy precipitation. In Alaska, mountain hemlock also comes down to sea level on organic soils along the edges of muskegs (spongy bogs). Both hemlock species grow well in partial shade, making them well suited to the dense, layered canopy of the coastal forest.
Several other conifers round out the southeast forest. Western redcedar, Alaska yellow cedar, silver fir, and subalpine fir all occur in this region. Alaska yellow cedar, a member of the cypress family, is a slow-growing coastal specialist that produces small winged seeds with low viability, limiting how far it can spread naturally. The only common deciduous trees in the coastal forest are black cottonwood and red alder, found mostly along riverbanks, streamsides, and recently disturbed ground.
Interior Boreal Forest: Spruce Country
Move inland past the Coast Range and you enter the boreal forest, Alaska’s largest vegetation zone, stretching from the Brooks Range in the north to the coastal mountains in the south. Two species of spruce define this landscape: white spruce and black spruce.
White spruce favors warmer, well-drained, nutrient-rich soils. Black spruce dominates the colder, wetter, nutrient-poor sites underlain by permafrost. Black spruce actually replaced white spruce as the most common interior tree roughly 4,000 to 5,000 years ago. That shift likely contributed to more frequent wildfires, since black spruce forests burn more readily. Today, climate change may be reshuffling the balance again. Research from the National Park Service suggests that widespread permafrost thawing could allow white spruce to expand at the expense of black spruce, while a wetter climate could give black spruce the competitive edge.
White spruce is also the dominant species at the northern tree line, where the boreal forest gives way to Arctic tundra across the Brooks Range. Some white spruce grow as far north as 72 degrees latitude, though these far-northern trees tend to be stunted and widely scattered.
Deciduous Hardwoods of the Interior
Alaska’s interior is not all spruce. Three deciduous hardwoods are common throughout the boreal zone: paper birch, quaking aspen, and balsam poplar.
Paper birch is the most recognizable, with its distinctive white bark that peels in papery strips. Young trees keep a golden or brown bark until about age 10 to 12, when the familiar white color develops. These are fast-growing trees. An individual birch can reach 8 inches in diameter in 30 years, though growth slows significantly with age. In Alaska, site quality is somewhat lower than in the eastern U.S., likely because permafrost and cold soils limit root development. Paper birch grows best on well-drained, sandy loams on cool, moist sites and commonly mixes with white spruce or black spruce. On cooler, moister slopes it tends to outcompete aspen, while aspen takes over on warmer, drier ground.
Quaking aspen is an aggressive pioneer species, meaning it quickly colonizes land after fires or other disturbances. In Alaska, it grows only on the warmest sites free of permafrost, favoring south and southwest-facing slopes that get the most sun. Repeated fires actually increase aspen density by triggering new shoots from existing root systems. Over centuries without fire, shade-tolerant spruce gradually replaces aspen, but this succession can take anywhere from one aspen generation to over 1,000 years.
Balsam poplar and its close relative black cottonwood fill out the deciduous roster, growing along rivers and floodplains where they can reach impressive sizes. These poplars are often the first large trees to establish on freshly deposited gravel bars and disturbed riparian areas.
Tamarack: The Oddball Conifer
Tamarack is one of Alaska’s most unusual trees. It’s a conifer that drops all its needles every fall, turning gold before going bare for winter. In Alaska, tamarack grows primarily in bogs underlain by permafrost, tolerating conditions that would kill most other trees: waterlogged soil, high acidity, and extremely cold ground temperatures. At the northern edge of its range, tamarack reproduces mainly through layering, where low branches touching the ground take root and grow into new stems, rather than relying on seeds.
Where Trees Stop Growing
Large portions of Alaska have no trees at all. The Arctic coastal plain, the western coast, the Aleutian Islands, and high mountain elevations are dominated by tundra, scrub vegetation, and grasses. The tree line in Alaska is controlled primarily by climate, running roughly along the southern slopes of the Brooks Range in the north and dropping to lower elevations in areas exposed to harsh coastal winds in the west.
White spruce marks most of Alaska’s northern tree line. Climate models predict that conditions suitable for tree growth now extend beyond current tree lines in several areas, suggesting forests could advance northward. However, factors beyond temperature, including soil conditions, seed dispersal limitations, and disturbance patterns, constrain how quickly that shift can actually happen.
Quick Reference by Region
- Southeast (Coastal Rainforest): Sitka spruce, western hemlock, mountain hemlock, western redcedar, Alaska yellow cedar, silver fir, subalpine fir, red alder, black cottonwood
- Interior (Boreal Forest): White spruce, black spruce, paper birch, quaking aspen, balsam poplar, tamarack
- Southcentral (Transition Zone): Mix of coastal and boreal species depending on elevation and proximity to the coast
- Arctic, Western, and Aleutian regions: Tundra with no significant tree growth