Somewhere between 6 and 9 percent of America’s forested land still qualifies as old growth, depending on which definitions and datasets you use. In absolute terms, that works out to roughly 25 million hectares across all land ownerships, with a much larger share of mature forest that has not yet crossed the old-growth threshold. Those numbers sound modest until you consider the starting point: before European settlement, old-growth forest blanketed the majority of what is now the lower 48 states, and in some regions the losses have been almost total. The picture gets more interesting when you look at where the surviving stands actually are, what they do that younger forests cannot, and how realistic it is to grow more of them.
The National Numbers
Two major federal-scale assessments, both spurred by a 2022 presidential executive order directing the U.S. Forest Service to inventory mature and old-growth forests, have produced slightly different tallies. One classified about 6.3 percent of current U.S. forested land as old growth and almost a third as mature.1Frontiers in Forests and Global Change. Classifying, inventorying, and mapping mature and old-growth forests in the United States A more recent mapping effort covering all land ownerships put the figure higher, at about 8.6 percent old growth (roughly 25 million hectares) and 43.7 percent mature (about 155 million hectares).2Environmental Research: Ecology. Baseline maps of U.S. mature and old-growth forests for conservation and management The gap between the two reflects differences in how regional definitions were applied and which data layers were fed into the models, not a disagreement about whether old growth is rare. Both studies agree on the broad picture: old growth is a small fraction of what it once was, heavily concentrated on public lands in the western states.
A separate analysis focused specifically on U.S. Forest Service National Forest System lands estimated roughly 10 million hectares of old growth on those federal lands alone, with most of it in the West.3Forest Ecology and Management. Quantifying old-growth forest of United States Forest Service public lands That figure represents the first nationally consistent old-growth assessment using the Forest Service’s own regional definitions applied to the national forest inventory. It tells us that federal forests hold a disproportionate share of the country’s remaining old growth, which matters for policy: management decisions on National Forest System lands directly affect a large percentage of the total.
What Makes a Forest “Old Growth”
There is no single birthday a forest celebrates to earn the label. Old-growth definitions vary by region and forest type, but they generally revolve around structural complexity rather than age alone. Compared with mature forests, old-growth stands consistently show higher densities of large living trees, wider average trunk diameters, more live aboveground biomass, and substantially more coarse woody debris on the forest floor.4Europe PMC. Commonality and variability in the structural attributes of moist temperate old-growth forests: A global review In practical terms, that means big trees (often several centuries old), a mix of canopy layers, standing dead trees called snags, and downed logs in various stages of decay. A Pacific Northwest Douglas-fir forest might need 200 or more years to develop those traits, while an Appalachian hardwood stand might cross the threshold sooner because its dominant species mature at different rates.
This variability is part of why estimates differ. Two researchers can walk through the same stand and disagree on whether it qualifies as old growth, because the checklist of structural markers shifts by region. The Forest Service uses different old-growth definitions for its nine administrative regions, a pragmatic approach that captures real ecological differences but makes national tallies inherently fuzzy around the edges.
The West Holds Most of What Remains
The Pacific Northwest alone once contained roughly 16.7 million hectares of old-growth conifer forest, covering about two-thirds of the region’s total land area. Approximately 72 percent of that original old growth has been lost, primarily to logging.5PubMed. Status of mature and old-growth forests in the Pacific Northwest Even so, the surviving stands in Oregon, Washington, and Northern California represent the largest contiguous blocks of old growth in the lower 48. The Central and Southern Cascades and the Klamath-Siskiyou region together account for nearly half of what is left. Over 78 percent of that remaining old growth sits on public land, which is why federal timber policy in the region carries so much weight.
Mature conifer forest in the Pacific Northwest nearly equals the area of old growth, which suggests a sizable pipeline of future old growth if those stands are left to develop. Whether they get that chance depends on management decisions, wildfire, and increasingly on climate-driven insect outbreaks. The region’s old growth is not frozen in time; it is constantly gaining at one edge as mature stands age in, and losing at another edge to disturbance.
The Eastern United States
East of the Mississippi, the picture is starkly different. Roughly 99 percent of the East’s original old-growth forest was cut down in fewer than 250 years of European settlement.6Forests. Mammals of Eastern Old-Growth Forests in the United States What survives exists as scattered remnant stands, often small and isolated: a cove of ancient hemlocks in the southern Appalachians, a tract of old-growth white pines in northern New England, a patch of centuries-old oaks on a steep slope that loggers skipped because it was not worth the trouble. Many of these patches are under 100 acres. Some are surrounded by second-growth forest and suburban development.
Because so little remains, eastern old growth has been enormously difficult to study. Researchers trying to understand how native mammals or plants depended on these forests have almost no baseline to work from. Still, the fragments matter. Dry-mesic old-growth oak forests, for example, are widely distributed across the East as remnants and are expected to expand in area as second-growth forests mature.7Earth. Characteristics of Dry-Mesic Old-Growth Oak Forests in the Eastern United States They offer a living reference for what much of the eastern landscape used to look like and could look like again, if given time.
Alaska’s Outsized Contribution
Alaska complicates the national math in a big way. The Tongass National Forest alone covers 6.7 million hectares and ranks among the world’s most intact temperate rainforests.8Land. The Tongass National Forest, Southeast Alaska, USA: A Natural Climate Solution of Global Significance It holds enormous volumes of old-growth Sitka spruce, western hemlock, and Alaska yellow cedar. Because much of the Tongass has never been logged at industrial scale, its old-growth acreage alone accounts for a large fraction of the national total. When you see national figures stating that 8 or 9 percent of U.S. forests are old growth, a substantial chunk of that percentage is sitting in southeast Alaska.
The Tongass has been a policy battleground for decades. Timber sales in the forest peaked in the mid-20th century, and the 2001 Roadless Rule restricted development on much of it, though that protection has been repeatedly challenged. The forest’s old-growth trees grow slowly in the cool, wet climate, meaning that harvested areas take far longer to recover structural complexity than forests in warmer regions.
Carbon Storage and Why It Matters for Climate
One of the strongest practical arguments for conserving old growth is carbon. Old-growth forests across the U.S. store roughly 224 metric tons of carbon per hectare, compared with about 201 for mature forests and 178 for young forests.9Biological Conservation. How much more carbon could be protected in mature and old-growth forests of the United States? The difference is not just in the living wood. Dead wood plays a disproportionate role: in Mid-Atlantic old-growth forests, dead wood carbon density was roughly 18 times higher than in surrounding younger forests.10PubMed. Carbon storage in old-growth forests of the Mid-Atlantic: toward better understanding the eastern forest carbon sink Those downed logs and snags are not waste; they are a carbon bank that took centuries to accumulate.
This is sometimes misunderstood. A common claim is that old-growth forests are “carbon neutral” because tree growth slows with age and decomposition roughly offsets new growth. While net carbon uptake does decline in very old stands, the sheer quantity of carbon already locked in the biomass and soil makes old-growth forests irreplaceable on any policy-relevant timescale. Logging a 500-year-old forest and replanting it releases a pulse of stored carbon that the replacement forest will not recapture for centuries, even under ideal growing conditions. From a climate perspective, the carbon already in the ground and in the wood is the point.
Fire Resistance and Microclimate Buffering
Old-growth forests interact with fire differently than younger stands. In the Pacific Northwest, old-growth habitat used by northern spotted owls was found to have a lower probability of burning at moderate or high severity compared with other forest types, even under high fire-weather conditions.11Ecosphere. Mixed‐severity wildfire and habitat of an old‐forest obligate The mechanisms are straightforward: large, thick-barked trees are harder to kill, the multi-layered canopy holds moisture, and the lack of dense understory brush in many old-growth types reduces the available fuel near the ground. This does not make old growth fireproof, but it does make severe crown fire less likely in many cases.
Dense old-growth canopy also buffers the understory from temperature extremes. Research on forest management and climate-change refugia has noted that this dense canopy is a key feature moderating understory microclimate, potentially shielding organisms from rising temperatures.12PubMed. Applying climate change refugia to forest management and old-growth restoration That buffering effect matters for species that cannot tolerate heat or dryness, from salamanders to shade-loving plants. As climate change intensifies, the few remaining old-growth stands may serve as islands of cooler, moister habitat in a warming landscape.
Canopy Ecosystems in Old-Growth Redwoods
Some of the most striking ecology in American old growth happens hundreds of feet above the ground. In old-growth redwood forests, the massive trunks of the largest trees develop reiterated limbs, essentially new trunks growing off the main stem, that accumulate soil, ferns, and even shrubs in the canopy. One study documented 13 species of vascular plants growing as epiphytes in an old-growth redwood plot, with virtually all of them restricted to the 14 largest trees. The canopy held over 2,300 kilograms of soil per hectare, enough to support an ecosystem that younger, smaller trees simply cannot replicate.13Ecological Monographs. Trunk reiteration promotes epiphytes and water storage in an old-growth redwood forest canopy These aerial gardens also store water, creating moisture reserves that buffer the canopy community during dry periods. No amount of replanting recreates this; it requires centuries of uninterrupted growth for a redwood’s architecture to become complex enough.
The Northwest Forest Plan and Federal Policy
The most significant policy intervention to protect old growth in the U.S. was the Northwest Forest Plan, adopted in 1994 to resolve conflicts between logging and the survival of the northern spotted owl and other old-forest species. In its first decade, the plan succeeded in protecting nearly all existing older forest on federal land from timber harvest, and older forest on those federal lands showed a net increase of over a million acres.14U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. Northwest Forest Plan—the first 10 years (1994–2003): first-decade results of the Northwest Forest Plan Federal timber harvest in the plan area averaged only about half of the plan’s own goals, partly because conservation constraints were tighter than anticipated.
The plan also included a Survey and Manage program that attempted to protect hundreds of rare species associated with late-successional and old-growth forests across more than 9.7 million hectares of federal land.15PubMed. Protecting rare, old-growth, forest-associated species under the Survey and Manage Program guidelines of the Northwest Forest Plan That program was unprecedented in scope and succeeded in shielding many species that traditional conservation programs overlook, though it generated friction with timber harvest goals. The broader legacy of the plan is clear: federal harvest dropped sharply, old-growth area on public land stabilized and grew, and the surrounding timber-dependent communities absorbed real economic pain.
How Long Does It Take to Grow Old Growth?
If old growth is so depleted, an obvious question is whether we can grow more of it. The answer is yes, with a very large asterisk: it takes a long time. A chronosequence study in coastal British Columbia (ecologically similar to the U.S. Pacific Northwest) found that the earliest second-growth stands to develop old-growth structural characteristics reached that threshold at around 112 years, while most required 200 to more than 250 years.16Canadian Journal of Forest Research. The temporal development of old-growth structural attributes in second-growth stands: a chronosequence study in the Coastal Western Hemlock zone in British Columbia Those timelines assume no further disturbance, no logging re-entry, and no catastrophic fire.
Some land managers are trying to speed up the process. Restoration thinning treatments in the coastal Pacific Northwest have shown empirical evidence of accelerating old-growth development, producing larger trees, more complex vertical and horizontal structure, reduced stand density, and increased understory plant diversity within a few decades of treatment.17Conservation Science and Practice. Forest restoration thinning accelerates development of old‐growth characteristics in the coastal Pacific Northwest, USA The idea is counterintuitive: selectively removing some trees gives the remaining ones more light and growing space, mimicking the natural thinning that happens in unmanaged forests over much longer periods. These treatments do not produce old growth overnight, but they can shave decades off the timeline for stands that are already partway there.
A competing approach, sometimes called proforestation, argues that the best strategy is to simply leave maturing forests alone and let natural processes do the work. Proponents note that every intervention carries risk (soil compaction from machinery, accidental damage to retained trees, loss of canopy density) and that the evidence for long-term acceleration remains limited. In practice, most forest managers use a mix of both approaches depending on site conditions and the starting state of the stand.
What Logging Old Growth Does to Water
One underappreciated consequence of old-growth loss involves hydrology. A 50-year study at the H.J. Andrews Experimental Forest in Oregon tracked what happened to streamflow after old-growth conifer stands were clearcut and replanted. Early on, fall runoff surged by as much as 99 percent in the first decade. By the third to fifth decade, it dropped below pre-harvest levels as the young planted forests consumed more water through transpiration than the old growth they replaced. Winter and spring runoff initially jumped 12 to 70 percent and remained elevated through the fourth or fifth decade. More than half a century after logging, there was no clear evidence of hydrologic recovery.18Hydrological Processes. Fifty years of runoff response to conversion of old‐growth forest to planted forest in the H. J. Andrews Forest, Oregon, USA
The practical meaning: old-growth forests regulate water flow in ways that planted forests do not replicate for decades, possibly longer. The thick canopy intercepts rain and snow, the deep root systems draw water from different soil layers, and the spongy forest floor of decomposing wood and organic matter absorbs and slowly releases moisture. Replacing that system with a plantation changes when and how much water reaches streams, with potential downstream effects on fish habitat, erosion, and water supply.
Indigenous Burning and the Forests That Existed Before
Discussions of old-growth loss sometimes treat European settlement as the beginning of human influence on American forests, but that framing ignores millennia of Indigenous land management. Historical descriptions compiled from across the eastern United States suggest that Indigenous burning had regional-scale influence on forested ecosystems, shaping species composition and stand structure long before industrial logging began.19International Journal of Wildland Fire. Compiling historical descriptions of past Indigenous cultural burning: a dataset for the eastern United States Frequent, low-intensity fire maintained open woodlands and grassy understories in many areas, creating conditions that favored fire-tolerant species like oaks and longleaf pines. The old-growth forests that Europeans encountered were not untouched wilderness; they were cultural landscapes shaped by deliberate management over thousands of years.
This matters for restoration. If the goal is to recover something like the pre-settlement old-growth condition, simply halting logging is not enough. Many eastern old-growth remnants are losing their oak dominance because fire suppression allows shade-tolerant species like maples and beeches to take over the understory. Prescribed burning, modeled on the fire regimes that Indigenous peoples maintained, is increasingly recognized as necessary for keeping these forests on their historical trajectory rather than shifting to a different forest type entirely.
Mapping the Future With Remote Sensing
Knowing how much old growth remains depends on being able to find and measure it, and the tools for doing that have improved dramatically in the past decade. The most recent national-scale effort used a Bayesian modeling framework that combined Forest Inventory and Analysis plot-level data with layers from both active and passive satellite remote sensing to produce probability maps of mature and old-growth forest across the contiguous United States.20Oak Ridge National Laboratory DAAC. Mature and Old-growth Forest Probability Maps for the Conterminous United States These maps do not simply mark stands as old growth or not; they assign each pixel a probability, reflecting the inherent uncertainty in satellite-based classification. Ground-based inventory plots remain the gold standard, but satellites and airborne lidar let researchers extend those ground measurements across landscapes that would be impossible to survey on foot.
Accuracy remains a challenge. Old-growth forests are rare, and rare classes are inherently harder for statistical models to detect reliably. A Finnish study using airborne lidar and satellite imagery found that plot size and the rarity of old-growth patches both significantly affected mapping accuracy.21Canadian Journal of Forest Research. Mapping old-growth forests using airborne lidar data and satellite images: how do plot size and rarity affect accuracy? The same issue applies in the U.S.: a 10-acre old-growth fragment surrounded by second-growth forest may not show up clearly in moderate-resolution satellite data. As lidar coverage expands and sensor resolution improves, the maps will sharpen, but for now, every national estimate carries a meaningful margin of uncertainty. That uncertainty is itself useful information for anyone trying to decide where conservation investments will do the most good.