Top Line: Supreme Court Justice Potter Stewart said it of pornography, but he could have applied the thought to old-growth forests as well: “I shall not today attempt further to define the kinds of material I understand to be embraced . . . but I know it when I see it.”
Figure 1. Old-growth ponderosa pine stand, Ochoco National Forest, Oregon. Source: Larry Olson (first appeared on the cover of Oregon Wild: Endangered Forest Wilderness, Timber Press, 2004).
Most of us know mature and old-growth (MOG) forests and trees when we see them, but just how much MOG forest does the US have left? Informed public debate depends on having this data. Unfortunately, several recent efforts to answer this question have left us with numbers that are all over the map.
Neither time now nor space here allow me to compare and contrast in detail the various MOG inventories. (Such is the subject of a Larch Company memorandum in production.) Here I will highlight the findings of the studies and point out some factors that may have led to the different outcomes.
All Over the Map
On Earth Day (April 22) 2022, President Biden issued Executive Order (EO) 14072, “Strengthening the Nation’s Forests, Communities, and Local Economies.” The EO directed the USDA Forest Service and the USDI Bureau of Land Management (BLM) to “develop policies . . . to institutionalize climate-smart management and conservation strategies that address threats to mature and old-growth forests on Federal lands.” This raised several questions: What exactly are mature and old-growth (MOG) forests or trees? How much MOG forest is left on Forest Service and BLM holdings? How much of such MOG forests and trees is there by forest types? Where is such MOG?
On April 22, 2023, thirty-four years after the logging of old-growth forests became an issue in the Pacific Northwest because northern spotted owl habitat was being clear-cut, the Forest Service and the BLM put out an initial inventory of MOG forests on their holdings. This followed the publication of three other MOG inventories, all undertaken in response to EO 14072 and published in scientific journals.
Comparing the findings is instructive, if not downright confusing. (Warning: Please don’t try to reconcile these numbers or your head may explode.) The extent of MOG forest on Forest Service and BLM lands in the conterminous US (the lower 48 states) may be
• 104+ million acres (Forest Service–BLM 2023),
• 66.8 million acres (DellaSala, Mackey, et al. 2022), or
• 59.7 million acres (Barnett et al. 2023).
Regarding the extent of MOG forest on Forest Service and BLM lands in Alaska, we know that
• 8.8 million acres of MOG forest have been counted, but this does not include any MOG that may yet be found on 3.4 million acres of Forest Service and 27.5 million acres of BLM lands in Alaska that have not been inventoried (Forest Service–BLM 2023), and
• 5.1 million acres of “productive old growth” (“mature” forest is not a thing) has been inventoried on the Tongass National Forest, but this doesn’t include significant amounts of old-growth shore pine (lodgepole pine) on muskeg (DellaSala, Gorelik, and Walker 2022).
Why the Differences?
Two of the inventories are limited to the conterminous United States, while one (kinda) includes Alaska. The study that focuses solely on Alaska doesn’t include the Chugach National Forest or any BLM forests. Most break out protected and unprotected MOG, while one does not. Some assume that to qualify as forest, a piece of land has to have at least 10 percent forest cover, while others assume 20 percent. Some map to a resolution of 30 by 30 meters (~0.2 acres), while one has a resolution of ~250,000 acres; the latter may be useful in telling us how much MOG there is but not where it is.
Additionally, the various inventories define “mature” and “old growth” differently and use different datasets. The Forest Service–BLM inventory is based on the Forest Inventory and Analysis (FIA) database that the Forest Service has been developing for nearly a hundred years. The Forest Service–BLM inventory comments:
The Federal approach applies existing definitions based on structural characteristics for old-growth forest types to FIA data. Barnett et al. (2023) also used FIA data but classified old-growth and mature forest based on the pattern of biomass accumulation. DellaSala et al. (2022) developed their classification based on remotely sensed data, emphasizing tall, high-biomass, and closed-canopy forests. The Federal approach stratifies forest into 200 regional vegetation types; the finer resolution of forest types results in an inventory accommodating greater variation in the expression of old-growth and mature forest characteristics, especially in low productivity types.
We’ll look at the Forest Service–BLM inventory first and then examine the three others that were prepared before the federal inventory came out.
Forest Service–BLM 2023: MOG on Federal Holdings in the Lower 48 and Portions of Alaska
I must preface this discussion of the Forest Service–BLM inventory by saying that the Forest Service and the BLM have never wanted to know just how much mature and old-growth forest they have. They have rightfully feared that to map the MOG will lead to protection of the MOG from logging.
Back in the day, when old growth first hit the spotted owl fan, the agencies assured the public that there was no shortage of old growth. However, when pressed to define and count its old growth, the Forest Service steadfastly refused to count and narrowly defined old-growth Douglas-fir as only the most cathedral-like stands (featuring a very large number of very large boles per acre), leaving out the vast majority of old-growth forests.
Now, compelled by President Biden’s executive order, the Forest Service and the BLM have issued the federal government’s first national inventory of MOG forests. The task was accomplished within a year’s time, and details of the methodology used by the agencies to define “mature” forest are not yet available. In defining “old growth,” the agencies relied on definitions issued by the Forest Service circa the early 1990s.
As part of the inventory, an online interactive map is available for Forest Service lands only (not BLM lands). Maps 1, 2, 3, and 4 are screenshots from the Forest Service online map. Use the key in Figure 2 to interpret the color meanings.
Figure 2. While reviewing the maps below, keep this color code in mind. Source: USDA Forest Service.
Map 1. MOG forests on national forest lands in Alaska, according to the Forest Service. Source: USDA Forest Service.
Map 2. MOG forests on national forest lands in the American West, according to the Forest Service. Source: USDA Forest Service.
Map 3. MOG forests on national forest lands in the American East, according to the Forest Service. Missing is the El Junque National Forest in Puerto Rico. Source: USDA Forest Service.
Map 4. MOG forests on national forest lands in Oregon, according to the Forest Service. Each polygon is on the order of a quarter million acres, rendering such maps mostly useless. The two indigo (darkest) polygons center on the South Fork McKenzie River and the Wenaha River watersheds. Source: USDA Forest Service.
Table 1 shows the acreage of MOG and younger forests on Forest Service and BLM forested lands in the lower 48 and Alaska by agency and land use allocation.
Table 2 shows the acreage of MOG and younger forests on Forest Service and BLM forested lands in the lower 48 and Alaska by FIA forest type group.
Both tables show a total of 112,770, 527 acres of mature and old-growth forest (80,112,137 acres of mature forest + 32,658,390 acres of old-growth forest) inventoried in the lower 48 and Alaska, although both also stipulate in the footnotes that the inventory “excludes 3.4 million acres of forested Forest Service land and 27.5 million acres of potentially forested BLM land in Alaska.” Some 8.8 million acres of MOG forest have apparently been counted in Alaska (see Map 1), the difference between the 112+ million acres shown in the tables and the figure of 104+ million acres for just the lower 48 given in running text in the inventory.
DellaSala, Mackey, et al. 2022: MOG on Lands of All Ownership in the Lower 48
The paper by DellaSala, Mackey, et al., “Mature and Old-Growth Forests Contribute to Large-Scale Conservation Targets in the Conterminous United States,” is a “spatially explicit MOG assessment based on three structural development measures—canopy height, canopy cover, and aboveground living biomass to assess relative maturity.” The paper considered all ownerships and major forest type groups. The data can generate maps at a resolution of 30 by 30 meters. Map 5 is a small-scale map from the paper. Wild Earth Guardians has kindly made available a set of maps at the scale of Forest Service regions (which differ from the regions shown in Map 5).
Mind the GAP
The US Geological Survey’s Gap Analysis Project classifies all lands as either GAP 1, 2, 3, or 4, from the most nature protection to no protection. GAP 1 and GAP 2 are protective enough to qualify in counting toward 30x30, i.e. conserving 30 percent of the nation’s lands and waters by 2030. In recognition that GAP 3 includes semi-protected Forest Service inventoried roadless areas and totally unprotected Forest Service Douglas-fir monoculture plantations in the same GAP code, DellaSala, Mackey et al. 2022 recognized the former as an unofficial “GAP 2.5.”
Map 5. Mature and old-growth forests in the contiguous US. Source: DellaSala, Mackey, et al. 2022.
Table 3 identifies 51.3 million acres of mature and old-growth forests that should be subject to an enduring regulation to conserve and restore mature and old-growth forests, and 66.8 million acres of mature and old-growth forests on all federal lands.
Table 4 categorizes MOG forest based on the Forest Service’s Forest Inventory and Analysis (FIA) framework.
Barnett et al. 2023: MOG on Lands of All Ownership in the Lower 48
In their paper “Classifying, Inventorying, and Mapping Mature and Old-Growth Forests in the United States,” Barnett et al. analyzed Forest Inventory and Analysis (FIA) data from the Forest Service and then merged it with TreeMap to develop maps at 30-by-30-meter resolution depicting “locations throughout the nation where concentrations of old-growth and mature forest may be high.” The paper considered all ownerships and major forest type groups (except for redwood and western white pine, which created data issues due to their minor extent). Map 6 is from the paper. The authors “view our map as suggestive rather than authoritative” and urge a “thorough field-based accuracy assessment.”
Map 6. Young, mature, and old-growth forests in the continental US. Source: Barnett et al. 2023.
Table 5 does not distinguish between FIA reserved and unreserved forest. It comes up with a total of 59,660,676 acres of MOG forest on Forest Service and BLM holdings.
The paper’s authors note:
The 38.7% of the forest estate [both federal and non-federal ownerships] in mature and old-growth stages, combined, is remarkably close to the 35.9% estimated by DellaSala [, Mackey,] et al. (2022), despite the use of very different classification and mapping methods.
Table 6 depicts the amounts of MOG forest types that are protected and unprotected.
DellaSala, Gorelik, and Walker 2022: MOG on the Tongass National Forest
The paper “The Tongass National Forest, Southeast Alaska, USA: A Natural Climate Solution of Global Significance” is primarily about carbon storage and sequestration on the Tongass National Forest, but it does yield some information about the amount of MOG forest on the Tongass, which contains the most carbon-dense MOG forest in Alaska. Table 7 shows forest types by area.
A few things to keep in mind:
• The Forest Service counts as “productive old growth” (POG) any naturally occurring Sitka spruce and/or western hemlock. Because of the natural history of these forest types in this area (a rainforest with little disturbance), there is no significant amount of “mature” forest. POG that has been clear-cut and has regenerated naturally is called “young forest” by the Forest Service. (See Map 7.)
Map 7. Productive old growth and young growth on the Tongass National Forest, Alaska. Source: DellaSala, Gorelik, and Walker 2022.
• “Other” includes nonforested landscapes such as glaciers as well as “productive old growth” (POG), primarily lodgepole pine trees (aka shore pine) on muskeg (“North American swamp or bog consisting of a mixture of water and partly dead vegetation, frequently covered by a layer of sphagnum or other mosses”). The lodgepoles are quite old but rather sparse in density, so there isn’t much classic “old-growth” character. Nonetheless, as the trees are several hundreds of years of age, the forest (or woodland) qualifies as “old growth.”
Some Caveats About the Federal Inventory
Because I had prepared myself for reading the federal inventory by first studying the other three papers mentioned above, I was pleasantly surprised by the numbers in the federal report. I never would have thought that the federal forest agencies would identify as much MOG forest as they did. It should be said that a large part of the identified MOG forest land is the ~24 million acres of pinyon-juniper woodlands found mostly on BLM lands in the American West.
Of course, while I like the big numbers in the federal tables, I must outline a few caveats:
• The amount of old-growth forest is actually higher than counted in the inventory. The agencies’ definition of “old growth” is based on the definitions developed by the Forest Service in the early 1990s, which were excessively restrictive so as to minimize the amount of “old growth” the agency feared at the time would be protected.
• The amount of mature and old-growth forest is actually higher than counted in the inventory. The agencies failed to inventory ~31 million acres in Alaska (but after all, it’s only been a state for nearly two-thirds of a century).
• The amount of mature forest may or may not be higher than counted in the inventory. As noted above, a significant amount of the forest feds identified as “mature” is, in fact, old growth. The agencies’ published inventory makes reference to yet-to-be-published scientific papers that explain how the agencies defined “mature” stands. I’ll know it when I see it.
I warned you that your head might explode.
For More Information
Barnett, K., G. H. Aplet, and R. T. Belote. 2023. “Classifying, Inventorying, and Mapping Mature and Old-Growth Forests in the United States.” Frontiers in Forests and Global Change 5:1070372.
DellaSala, D. A., S. R. Gorelik, and W. S. Walker. 2022. “The Tongass National Forest, Southeast Alaska, USA: A Natural Climate Solution of Global Significance.” Land 11:717.
DellaSala, D. A., B. Mackey, P. Norman, C. Campbell, P. J. Comer, C. F. Kormos, H. Keith, and B. Rogers. 2022. “Mature and Old-Growth Forests Contribute to Large-Scale Conservation Targets in the Conterminous United States.” Frontiers in Forests and Global Change 5:979528.
USDA Forest Service and USDI Bureau of Land Management. 2023. “Mature and Old-Growth Forests: Definition, Identification, and Initial Inventory on Lands Managed by the Forest Service and Bureau of Land Management: Fulfillment of Executive Order 14072, Section 2(b).”
Bottom Line: Any inventory reveals that most of the nation’s mature and old-growth forests have fallen to the saw. Not only must all that remains remain, but degraded forests should also be allowed to become mature and old-growth forests once again.