This is the second in a series of two Public Lands Blog posts on big old trees. Part 1 exploded the myth that big old trees slow in their rate of growth as they age and also introduced the concept of tree-related microhabitats. Part 2 examines a new scientific paper on the state of medium-sized and large trees in the United States.
So how are the big old trees in the United States doing? Surprisingly better than I would have thought—though by no means guaranteed into the future.
In 2023, the Forest Service and the Bureau of Land Management reluctantly completed an inventory of mature and old-growth forests on their lands. Acreage estimates by species group, land ownership, and such were prepared. Albeit with some significant gaps, this has been the best effort to date to assess the extent of such forests.
See Public Lands Blog post “How Much Mature and Old-Growth Forest Does the US Have Left?”
Now comes a new scientific paper (Chisholm and Gray 2025) that plumbs the depths of this inventory. Rather than looking at the age of stands, these authors focused on the size of trees by species. They state in their paper:
To conserve large-diameter trees, it is important to identify where they exist, the current rate of population change, and which species may be most vulnerable. The US Forest Service’s Forest Inventory and Analysis (FIA) program, which maintains a national network of over 140,000 repeatedly measured forest research plots spanning all ownerships, is an excellent resource for addressing these questions. [link added]
In this post I liberally quote from the three-page paper while interspersing some commentary for context.
Overview and Rationale for the Study
Let’s get an overview by reading the abstract:
Large-diameter trees provide vital ecological functions in forested ecosystems. Old, large-diameter trees may also be vulnerable to climate-driven mortality events, but past work on large tree populations has been geographically limited. Here, we characterize the population of large diameter trees from two size categories, 50 to 100 cm diameter at breast height (DBH) (medium) and >100 cm DBH (big), within the United States using Forest Inventory and Analysis data. Although populations of big trees are concentrated along the west coast, populations of medium trees are more evenly distributed across the nation. In the western United States, trees >50 cm DBH comprise ~75% of the total carbon stored in live trees, while in the eastern United States they comprise ~20%. Plot remeasurement data indicate that populations of big trees are increasing at an annual rate of 0.49% in the west and 2.9% in the east, and populations of medium trees are increasing at an annual rate of 0.5% in the west and 2.4% in the east. One exception is the Sierra Nevada region, where big trees are declining. Additionally, we observed declines for several individual species. While the overall population trend for large-diameter trees is positive, declines in these species could have localized impacts for the environments in which they occur. [emphasis added]
Why Count the Trees?
The authors open with an explanation of why they did the study:
Large-diameter trees are important components of forested ecosystems. Research has documented recent die-offs of large-diameter trees, and mortality rates are projected to rise due to climate change. Evidence suggests large-diameter tree mortality may be exceeding recruitment [growth of young trees into larger trees], though other studies indicate population stability. Because they store substantial amounts of carbon, a decrease in large-diameter tree populations could have serious implications for forest carbon storage. [emphasis added, citations omitted]
Who Owns the Big Trees?
Forested land in the United States consists of a matrix of different ownerships and varying levels of legal protection, and few studies have examined demographic trends outside of protected public land.
The authors didn’t break out medium-sized and big trees by land ownership, but had they, most would be on public lands, primarily federal public lands. Statistically, I hazard to guess, no large trees would be found on industrial private lands.
The Good News
Across the country, populations of large trees were generally stable to increasing. Populations of big and medium trees increased by 0.49% and 0.50% per year, respectively, in the western United States, and 2.9% and 2.4% per year in the eastern United States. [emphasis added]
Further:
Statistically significant increases in the big tree population were observed for P. menziesii [Douglas-fir], Populus balsamifera [balsam poplar], Sequoia sempervirens [coast redwood], Thuja plicata [western redcedar], and Picea sitchensis [Sitka spruce] in the west, and L. tulipifera [tulip poplar], Acer saccharinum [silver maple], Taxodium distichum [bald cypress], and Quercus virginiana [southern live oak] in the east. [emphasis added]
When one digs through the supplemental information accompanying the paper, one realizes that the number of mature and large trees for several species is going in the right direction.
Just How Many and at What Density?
The total population of trees >100 cm DBH (“big”) on forestland was estimated to be 81 ± 3.0 million in the western United States (0.82 ± 0.019 trees/ha), compared to 12 ± 1.3 million in the east (0.073 ± 0.0053 trees/ha).
So the western US has between 78 and 84 million large trees (0.33 such trees per acre), and the eastern US has between 10.7 and 13.3 million large trees (0.30 such trees per acre). This is in all forested areas, so it includes a lot of cutover and heavily managed forestlands.
The total population of medium trees was estimated to be 1.5 ± 0.02 billion in the west (16 ± 0.14 trees/ha) and 1.6 ± 0.02 billion in the east (9.9 ± 0.079 trees/ha).
So the western US has between 1.48 and 1.52 billion medium-sized trees (4 such trees per acre), and the eastern US has between 1.58 and 1.62 billion medium trees (6.5 such trees per acre).
These medium and large trees are spread across ~408 and ~247 million acres of US eastern and western forests respectively.
Where’s the Carbon?
Only 0.1% of all western trees were larger than 100 cm, and 1.9% were between 50 and 100 cm, with the implication that the top ~2% largest trees accounted for 75% of the live tree carbon storage in the western United States. This result suggests the importance of maintaining large-diameter trees in the western United States in order to mitigate climate change. [emphasis added]
Eastern US forests, which have a greater number of medium-sized trees than forests in the West, are also important carbon sinks.
Figure 9. The number of medium-sized tulip poplars is increasing. The Gennett Poplar on the Chattahoochee-Oconee National Forest in Georgia is not a medium-sized specimen. It is at least three hundred and possibly five hundred years old or older and is the second-largest tree in Georgia. Somehow it avoided the widespread logging during the late nineteenth and early twentieth centuries. Source: EcoAddendum.
The Less-Than-Good News
While “generally stable to increasing” is the right direction for populations of large trees, the adequate restoration of mature and old-growth trees will take a very long time. According to Chisholm and Gray:
Despite these observed increases, overall current densities were lower than large-tree densities observed in many old-growth forests, indicating that the landscape remains a matrix of stands from different successional stages. Further, at observed rates of increase, it would take considerable time for large-tree densities to approach precolonial levels. [emphasis added]
Something to look forward to.
Trees in Decline
A significant decline of −0.42% big trees/year was observed in one province, the Sierra Nevada. This may be due to drought, fire, and bark beetle disturbances in this region 2015 to 2020. To the extent that mortality in some areas has increased in recent years, the FIA averages across multiple remeasurement panels will not fully reflect those recent trends.
While the overall trend points to increases in large-diameter tree populations, mortality is outpacing recruitment for several species. Within the big size class, Pinus lambertiana [sugar pine], Abies magnifica [red fir], and Calocedrus decurrens [incense cedar] are exhibiting statistically significant declines. These species are most abundant in the Sierra Nevada. . . .
Within the medium size class, statistically significant reductions were observed for seven species nationally. Populations of medium-sized Abies lasiocarpa [subalpine fir], Picea engelmannii [Engelmann spruce], and Pinus albicaulis [whitebark pine], three species found in western subalpine environments impacted by a complex of native and introduced pests/diseases, were declining. Medium trees from three species located in low-elevation western woodlands—Quercus douglasii [blue oak], Alnus rhombifolia [white alder], and Quercus wislizeni [interior live oak]—were also declining, as was Fraxinus americana [white ash], an eastern species recently affected by an exotic woodborer. [emphasis added]
Whitebark Woes
Declines in large-diameter subalpine trees could have long-term impacts, because environmental limitations on productivity in subalpine habitats suggest large trees are unlikely to be quickly replaced after they die. P. albicaulis [whitebark pine], in particular, exhibited the highest rate of decline. At the current rate, the population of P. albicaulis 50 to 100 cm DBH will be halved every 16 y[ears]. [emphasis added]
In 2023, whitebark pine was listed as threatened under the Endangered Species Act (ESA). In Trump’s Timber Über Alles executive order, basically as an aside, he ordered the Fish and Wildlife Service, the Bureau of Land Management, and the Forest Service to complete the Whitebark Pine Rangewide Programmatic Consultation under section 7 of the ESA within 120 days. Big Timber seems worried, but I cannot see why. The Forest Service has repeatedly said, “Whitebark pine is of limited commercial use, but it is valued for watershed protection and esthetics.” The National Park Service notes the importance of the species to wildlife: “Although whitebark pine has very little commercial value, its seeds provide seasonal forage for a variety of wildlife, including grizzly bears, red squirrels, Clark’s nutcrackers, and a variety of granivorous small mammals.”
What of Ponderosa Pine?
How are those yellow-bellies (a.k.a. pondies or pondos)—arguably the most argued-about tree species in the American West—doing? Digging into the supplemental information that accompanies Chisholm and Gray (2025), one finds for the biggies a population decrease of 0.6±1.1 percent (it could be as high as a 1.7-percent decrease or as low as a 0.5-percent increase), which the authors deem not significant. As for medium-sized trees, the number is a 0.8±0.2 percent increase (as high as 1.0 percent or as low as 0.6 percent), which is significant.
A Demographic Bubble?
The reasons for the proliferation of large-diameter trees in the United States are unclear, but past management may have played a role in creating a demographic bubble of sub-mature trees that are now growing into larger diameter classes. Much of the productive timberland in the western United States was harvested in the previous century, but timber harvests on federal land have slowed during the past three decades. In the eastern United States, many forests are maturing after recolonization of former agricultural areas. If it is true that the current proliferation of large-diameter trees is due to a demographic bubble created by past human activities, then we would expect the nationwide population increase of large-diameter trees to be driven by elevated recruitment, not by diminished mortality.
An examination of mortality rates indicates that diminished mortality is unlikely to be the cause of the population increase, as our observed mortality rates for large-diameter trees are roughly equal to or greater than background mortality rates observed in old growth. Recruitment rates, on the other hand, range up to 4%, exceeding past observations from unmanaged old-growth forests. Rates of removal (i.e., harvest by humans) and outgrowth (trees that have grown out of the medium size class) were generally negligible components of change. Consequently, the relatively high observed mortality rate is being compensated by an even higher recruitment rate. This supports the hypothesis of a demographic bubble created by past human activity. [emphasis added, citations omitted]
While logging is “generally negligible” as a mortality factor, it is a factor that we humans have total control of (although the BLM and the Forest Service are quite out of control regarding logging of mature and old-growth forests). Given the huge deficit of mature and old-growth trees compared to precolonial times, logging any older trees is unacceptable.
In general, recent disturbances, such as drought, fire, insects, and disease, have not killed enough large-diameter trees to offset the recruitment of new individuals into these size classes (though our study does not adequately describe the very largest trees on the continent, which grow much larger than 100 cm DBH). However, outliers exist, including the Sierra Nevada region and several subalpine tree species. If this population increase is fueled by a human-created demographic bubble, unmanaged old-growth forests would be unlikely to see the same elevated recruitment and associated population increase. Overall, the increase in large-diameter tree populations across the United States is positive, but region- and species-specific declines may be causes for concern. [emphasis added, citations omitted]
A Recent Trend Does Not a Future Make
Although for more tree species than not, the number of medium-sized (20+ inches dbh) and large (39+ inches dbh) trees is increasing, this increase comes now after a time of massive decrease that started in 1630, according to the Forest Service. In addition, medium-sized and large members of several tree species are in decline. For these tree species, special attention must be paid.
Chisholm and Gray (2025) make clear that for many medium-sized and large tree species, recruitment is outpacing mortality and removals (see Graph 1). The best that can be done is to end removals (a.k.a. logging)—also a good idea, because every mature and large tree that is turned into logs is a carbon bomb exploding into the atmosphere.
“Removal” rates may skyrocket if Trump’s Timber Über Alles executive order is successfully executed.
See Public Lands Blog post “Trump 2.0 and the Nation’s Federal Forestlands”
Further Research
Building on Chisholm and Gray (2025), here are some possible directions for further research:
1. Break out the results for medium-sized and large trees of particular species by major land ownership.
2. Further differentiate large trees. The “large” category, defined as including any tree greater than ~39 inches dbh, includes everything up to the General Grant giant sequoia, which measures 432 inches or 36 feet dbh, more than ten times the minimum to qualify for the category. Perhaps we need a naming convention that keeps “large” but adds these classes: jumbo, huge, gigantic, mammoth, colossal, enormous, and unfuckingbelievable. Alternatively, the nomenclature could follow that for clothing: X-large (extra-large), XX-large (double extra-large), XXX-large (triple extra-large), and so on.
3. Model the trajectory of increase in the number of medium-sized and large trees in the United States (at least on public lands) in the case where they were no longer subject to “removal” (a.k.a. logging and removing to the mill), and also the amount of carbon stored and sequestered by these trees in this case.
4. Further interpret and present the findings of Chisholm and Gray (2025) in supplemental information on both the direction and intensity of change for each tree species.
For More Information
Chisholm, Paul J., and Andrew N. Gray. 2025. “Populations of Large Diameter Trees Are Increasing Across the United States.” Environmental Sciences 122(11): e2421780122.
Bottom Line: While the number of big trees in the United States has generally been increasing, this increase is from an impoverished baseline and will soon reverse if Big Timber gets its way.
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