Old-Growth and New Forests in Alaska’s Noatak National Preserve

Noatak National Preserve in northern Alaska is mostly Arctic tundra. But in a few places, forests of white spruce (Picea glauca) and balsam poplar (Populus balsamifera) grow — right at the cold edge of where trees can survive in northwestern North America. The National Park Service's Arctic Inventory and Monitoring Network, which monitors vegetation and landscape change across five park units in northern Alaska, studied how these trees grow and change.

White spruce forest along the Kelly River. Image from the National Park Service's 2023 vegetation monitoring brief for Noatak National Preserve.

How the forests are studied

The Arctic Network has nearly 500 permanent monitoring plots, 93 of them with trees. For this study, scientists cored trees and measured diameters and heights at 34 permanent plots, then compared growth rings with weather records and with the dates of historic volcanic eruptions. Plots are revisited roughly every 10 years; so far, 45 wooded plots have been remeasured. Crews measure every tree taller than 4.5 feet (1.37 m) and count seedlings in four subplots, and in the lab they count and measure the annual rings in the cores.

What they found

• Real old growth. White spruce forests on mountain slopes meet the U.S. Forest Service definition of old-growth forest. Trees older than 200 years are common, and a few are more than 300. Such forests grow in the Agashashok, Kelly and Kugururok river valleys, all tributaries of the Noatak.
• New forests. Younger stands that took root in the 1900s grow near tree line in the mountains, in small patches on rolling tussock tundra, and on river terraces and floodplains. The tree-line and tundra stands are probably spreading as the climate warms; the floodplain trees colonized newly exposed river bars.
• A slow response to weather. Ring widths vary a lot from year to year but respond surprisingly weakly to single hot or cold years, or to the cold years after volcanic eruptions. The clearest volcanic signal came from Tambora, in Indonesia, in 1815, which seems to have slowed growth in most trees alive at the time.
• Three to five years of memory. Most trees' diameter growth tracks warm or cold temperatures averaged over the previous three to five years — probably because warmth and cold build up effects on soils, nutrients and tree physiology.
• Still growing. All the forests, old and new, kept growing and adding wood between the first visits in 2011 and return visits in 2021 or 2022.

Old-growth white spruce near the Agashashok River; some of these trees are more than 300 years old. Image from the National Park Service's monitoring brief.

Sparse white spruce near tree line along the Agashashok River, mostly established in the 1900s. Image from the National Park Service's monitoring brief.

What it means for managers

• The old-growth forests are a unique resource. The trees are generally small — under 10 inches (25 cm) across — and far from settlements and travel routes, so they are unlikely to be sought for subsistence timber.
• Forests are expanding, but slowly — barely perceptibly within a human lifetime. The new forests are interesting and locally important, but they won't bring major ecological change to the preserve's landscapes in the coming decades.

The full NPS Natural Resources Report has the details.

Sources

Based on "Old Growth and New Forests in the Noatak National Preserve," Terrestrial Vegetation Monitoring Brief (2023), Arctic Inventory and Monitoring Network, National Park Service; a work of the United States government in the public domain.