Old-growth forests represent unique and irreplaceable ecosystems that have developed over long periods with minimal human interference. These ancient woodlands, characterized by complex structures and diverse life, once covered vast expanses of the United States. Today, their abundance has significantly diminished, making their remaining presence a subject of considerable interest and concern.
What Makes a Forest Old Growth?
Old-growth forests are defined by a collection of specific characteristics, rather than solely by tree age. These ecosystems exhibit complex structural diversity, including trees of various sizes and ages, a multi-layered canopy, and significant amounts of large deadwood such as standing snags and fallen logs. The presence of these features indicates a long period without major disturbances, allowing the forest to reach a late successional stage of development.
While age is a factor, the specific age for classification varies depending on tree species, geographic location, and site productivity. The defining attributes extend beyond just old trees to include canopy gaps created by tree deaths, pit-and-mound topography from fallen trees, and intact soils supporting a healthy fungal network.
Where US Old Growth Forests Remain
Estimates indicate a relatively small percentage of original old-growth forest remains in the United States. Historically, over 90% of these forests in the lower 48 states have been cleared since 1600. Current figures vary due to differing definitions, but generally, less than 7% of U.S. forests today are considered old-growth.
A 2023 federal inventory identified over 32 million acres of old-growth forests on public lands managed by the U.S. Forest Service and Bureau of Land Management, representing about 18% of all forested land under their care. This inventory included significant areas in Alaska, contributing to higher estimates than previous studies. The most extensive old-growth forests are found in Western states like Idaho, California, Montana, and Oregon. Remaining old-growth can also be found in New England, around the Great Lakes, and in Southern states, including specific areas within the Tongass National Forest, Ouachita National Forest, and Great Smoky Mountains National Park.
Why These Forests Matter
Old-growth forests provide ecological services that younger forests cannot fully replicate. These ecosystems are biodiversity hotspots, supporting a wide range of plant and animal species, many rare or endangered, that rely on their complex structures. Their multi-layered canopies and abundance of deadwood create diverse microhabitats, fostering rich communities of organisms from fungi to large mammals.
Beyond biodiversity, old-growth forests play a substantial role in carbon sequestration and storage. They absorb carbon dioxide from the atmosphere, storing it in their trunks, branches, roots, and soils, helping to mitigate climate change. These forests also contribute to water quality regulation by stabilizing soil, preventing erosion, and influencing hydrological cycles, which helps maintain clean water sources.
Protecting Remaining Old Growth
Efforts are underway to preserve the remaining old-growth forests in the United States. Federal agencies, such as the U.S. Forest Service and Bureau of Land Management, are developing policies to conserve these areas. These initiatives aim to protect existing old-growth and promote the development of mature forests into future old-growth stands.
Conservation strategies include designating areas as Wilderness Areas or National Parks, which offer protections against logging and other disturbances. Private conservation groups also work to identify and protect old-growth forests. Despite these efforts, challenges persist, including continued logging pressures, the impacts of climate change, and the need to balance conservation with local economic needs.