Forest Carbon, AMC’s Maine Woods and Net Zero

Throughout the period of European settlement in the United States, forests were a carbon source as they were cleared for development, agriculture, building materials, and energy.  The U.S. Forest Service estimates that about 60% of the carbon stored in pre-settlement forests was lost due to clearing and burning. 

Forests transitioned to a carbon sink around the beginning of the 20 ^th  century due to the replacement of wood by fossil fuels as the country’s primary energy source (which created a different set of problems), and by the abandonment of most agricultural land in the eastern United States followed by regrowth of forests across the region.  

Between 1630 and 1910 forest cover declined from about 46% of the country’s land area to 34% [1] . Since that time forest cover has remained relatively stable, as the gain of forest in the east has balanced the loss of forest to development across the nation.

 [1]   U.S. Forest Resource Facts and Historical Trends (usda.gov) 

The highest level of carbon storage in live trees is in the old growth forests of the Pacific Northwest and California. Carbon stocking in eastern forests is quite variable, with the highest levels in the southern Appalachians, the Allegheny Plateau, the Adirondacks and Catskills, and central New England.

Recent data shows that U.S. forests have continued to serve as a carbon sink since at least 1990. Since then, carbon in above- and belowground living biomass has increased by nearly 19%. Annual carbon sequestration in U.S. forests offsets about 10 to 15% of the country’s greenhouse gas emissions.  [1] 

However, not all trends are positive. While forests in most states continue to be carbon sinks, forests in some Rocky Mountain states have recently become carbon sources due to the effects of drought, insect and disease epidemics, and forest fires.

 [1]   R&D Hot Topic: Forest Carbon Status and Trends (usda.gov). 

New England’s forests reached their lowest extent due to agricultural clearing in the second half of the 19 ^th  century. The clearing was most extensive in southern New England; in northern New England (particularly Maine) more of the land has remained continually forested since it was less suitable for agriculture and settlement. 

A long period of agricultural abandonment led to the regrowth of much of the original forest area. However, after peaking in the 1970s, New England’s forests have now entered a second wave of forest loss, this time driven by residential and commercial development.

This history is reflected in the current age-class distribution of New England’s forests. Because large-scale natural disturbances are relatively rare in our region, prior to European colonization much of New England supported older forest (>150 years since major disturbance). In some areas, such as southern and coastal areas and major river valleys, disturbance was more frequent due to greater incidence of hurricanes and fires and the land management activity of Indigenous people. 

Because of the extensive clearing and harvesting over the last 400 years, New England’s forests are now much younger than in pre-Colonial times, and older forest has been almost totally eliminated. In five of the states, forests between 60 and 100 years old occupy over two-thirds of the landscape.  [1]  Maine has even more young forest due to ongoing commercial timber harvesting across large parts of the state. 

[1] Data were obtained from the U.S. Forest Service’s nationwide Forest Inventory and Analysis (FIA) program. Most forest stands in our region will contain trees of different ages, and do not have a well-defined starting point (as would be created by a clearcut). The FIA procedure bases a stand’s age on the age of dominant overstory trees, though there may be scattered older trees and many younger trees.

The story of New England’s forests is also seen in the pattern of forest carbon stocking across the region.

The extensive non-forested areas (yellow) represent permanent development and agricultural land, including much of eastern Massachusetts; the Hudson, Mohawk, St. Lawrence, Champlain, and lower Connecticut River valleys; and northeastern Maine. 

The highest carbon stocking (dark green) is found on large long-standing public lands (Adirondack and Catskill State Parks in New York, Green Mountain National Forest in Vermont, White Mountain National Forest in New Hampshire, and Baxter State Park in Maine), as well as more topographically rugged areas that were less suitable for agriculture and development, primarily southern Vermont, southwestern New Hampshire, and western Massachusetts. 

The lowest carbon stocking (light green) in the region’s forests is found across much of northern and eastern Maine and smaller areas of northern New Hampshire and northeastern Vermont. Much of this area was never cleared for agriculture, and ownership has long been dominated by large commercial timberland owners. The type of owner has changed over time, from the timber barons of the 1800s to the paper companies of the 1900s to the timberland investment organizations of the 2000s. However, for nearly two centuries the primary goal of these owners has been financial return from timber harvesting (either directly or indirectly as a source of fiber for lumber and paper mills).

The most recent data from the Forest Service’s FIA program shows that the average aboveground live tree carbon stocking in New England’s forests is about 25 metric tonnes of carbon per acre (mT C/ac) – about half of the level estimated from remaining old growth forests in the region.  [1] 

For five of the states, average carbon stocking is between 29 and 35 mT C/ac, while in Maine it is much lower – about 19 mT C/ac. In Maine there is a clear distinction between the eight smaller southern counties averaging 27 mT C/ac (where forest ownership is primarily in smaller tracts owned by individuals and families, similar to other parts of rural New England) and the eight northern counties averaging 18 mT C/ac (dominated by large commercial ownerships).

Commercial timber management has changed from the liquidation of the original old growth forests to the current approach focused on the efficient production of timber using modern forest management techniques. While sustainable from a timber production standpoint, the harsh reality of economics is that there is no financially rational reason to grow big old trees or maintain high timber volumes in the forest. Commercial ownerships will inevitably be dominated by younger, lower-volume and lower-carbon forests as compared to other areas across the region.

 [1]  State data from USFS Forest Inventory and Analysis; old growth data from Hoover et al., Benchmark carbon stocks from old growth forests in northern New England, Forest Ecology and Management 266 (2012).

Carbon stocking increased in all New England states between 2007 and 2019, indicating that they are continuing to function of carbon sinks. Over this period aboveground live tree carbon increased by 12 to 14% in the three southern New England states and about 9% in northern New England. 

This does not reflect the continuing loss of total forested area. However, over this period the increase in carbon on the remaining forest was more than enough to offset the loss of forest area, such that the total forest carbon increased in all states. However, this is unlikely to continue indefinitely.

Harvest levels are just one of many factors that determine carbon stocking levels, but there is a clear inverse relationship between statewide harvest levels and statewide live tree carbon stocks. States with more harvesting have lower average carbon stocks, and vice versa. Due to the dominance of large commercial forestland owners, Maine’s lower carbon stocking makes it a significant outlier compared to the rest of New England. 

However, there is a flip side…

Timber management varies widely, from commercial ownerships where financial return is the primary consideration, to government, non-profit and smaller private ownerships where ecological and social values are more important, to family forests where timber may only be harvested occasionally or not at all. There are significant tradeoffs that need to be considered - as a general rule, the greater the intensity of timber production, the greater the rate of carbon sequestration but the lower the average level of carbon storage (since large, slow-growing trees are removed).

Debates over the “production” versus “natural” approaches to forestry are not new, but go back as far as the beginnings of forestry in this country. Aldo Leopold captured the distinction in A Sand County Almanac (1949).

For much of the 20 ^th  century, Group A forestry was dominant among foresters and land managers. “Sustainable forestry” meant the sustainability of timber production. Old forests were often described as “overmature”, “decadent”, “stagnant” or “biological deserts”. However, advances in the scientific understanding of forest ecology in recent decades has made clear that a focus on efficient timber production does not ensure the sustainability of forest ecosystems and the species that depend on them. In particular, older, complex forests are not decadent - in addition to having high carbon stocks, they are among the most biologically rich parts of the landscape. 

Today, Group B forestry goes by many different names including “ecosystem management”, “ecological forestry”, or “exemplary forestry”. Whatever it is called, these approaches focus on maintaining the composition, structure and functions of natural forests, and using natural disturbance patterns as a guide to timber harvesting.  

Let’s examine the difference with two (very simplified!) examples, recognizing that these don’t come close to describing the diversity and complexity of actual forest management.

First is a traditional approach focused on timber production. 

We start with a two-storied stand, which is a very common condition following partial harvests (A). The overstory consists of trees large enough to be commercially harvested (generally greater than 6” to 8" diameter), while the understory consists of smaller seedlings and saplings.

This type of stand may result from a well-planned "shelterwood", in which the overstory is removed in two or three stages over 10 to 20 years. This allows for desirable species to regenerate under the protection of partial shade.  Usually the residual overstory consists of higher-value trees to provide a seed source. However, this type of stand may also result from a “high-grade” or “diameter-limit” harvest, in which the largest or most valuable trees are harvested, leaving a lower-quality overstory. A recent study estimated that 40% of the forest in northern New England was in a degraded condition based on the stocking of good quality trees. [1]

Eventually the remaining overstory is removed, leaving a young even-aged stand (B). This type of stand may also be created after a clearcut.

[1] Gunn, J.S., M.J. Ducey and E. Blair. 2019. Evaluating degradation in a North American temperate forest. Forest Ecology and Management 432: 415-426.

The residual stand is allowed to grow until the trees reach commercial size, at which point the stand is thinned (C). 

Once the stand reaches “commercial maturity”, a first entry shelterwood harvest is conducted to open up the canopy and promote new regeneration (D). For hardwoods this is usually at a diameter of 10” to 16” or an age of 60 to 80 years; for spruce-fir stands it may be even earlier (40 to 60 years).

Once regeneration is established (E), the overstory is removed, leaving a young, even-aged stand (F) and the cycle repeats.

This shelterwood system is just one of the many ways forests can be managed, but it constitutes about 40% of the area harvested each year in Maine, and nearly 60% on the large commercial ownerships.

The result is management that efficiently produces wood fiber but never develops large old trees, accumulations of large dead wood, or significant structural complexity. While young, shrubby stands (referred to as "early-successional") provide important habitat for some species, most of the cycle is spent as structurally simple "mid-successional" stands that have the lowest value for biodiversity. It also maintains relatively low average carbon stocking over the life of the cycle.

Now let’s look at a Group B approach, starting from the same point (A). 

Rather than a complete overstory removal, some mature trees are retained, an approach known as “deferred" or "continuous cover" shelterwood (among other names) (B).  The goal is to develop a multi-aged condition that retains mature trees throughout the life of the stand.

As before, the stand is thinned when the understory reaches commercial size (C). 

Eventually a new shelterwood establishment harvest is conducted (D). However, at this point the residual overstory has developed more large old trees (both live and dead), some of which will be permanently retained as “biological legacies”. These "late successional" features are disproportionately important for both carbon storage and maintaining biodiversity.

As before, a new cohort of regeneration is established (E). 

At this point there are several options. The deferred shelterwood approach can be continued, cycling through stages (C), (D) and (E) (thinning – shelterwood establishment - regeneration) while continuously maintaining a mature and structurally diverse overstory. The stand never returns to a young even-aged stage. 

Another option is to transition to continuously maintaining a mature multi-aged structure (F). Rather than harvests focusing on one aspect of the cycle (such as thinning or regeneration), stands are harvested on a 15- to 20-year cycle, with each harvest being a combination of thinning across all diameters and regeneration in smaller openings. At this point the stand has transitioned to "uneven-aged" management.

These approaches that focus on continuously maintaining a mature forest will support higher average carbon stocking than a Group A approach. They will contain higher levels of structural diversity and biological legacies, with benefits for both biodiversity and climate change resilience, while still providing a sustainable supply of timber. They are well-suited to growing high-quality sawlogs of desirable species such as sugar maple, yellow birch and red spruce, which are the most likely to be used for long-lived wood products such as structural lumber, flooring and furniture.  

This type of management will have a lower financial return, particularly in the near term. Transitioning from younger, lower-carbon forests to older, higher-carbon forests will involve a period of harvesting less than growth before a long-term sustainable harvest level is reached. Many trees will be allowed to grow beyond the financially optimal age, and higher losses to mortality are accepted. There is also a higher risk of losing significant value from natural disturbance events. The difference in revenue between a commercial and a more ecological approach may be considered "the tax we pay to the earth”.

The distinction between the two approaches can be seen in the contrast between two adjacent properties in northern Maine. On the left side of the image is the intensive management of a large commercial landowner. On the right is the much less intensive management on Maine state lands, which maintains more mature forest and higher carbon storage.

However, land is managed, there are two critical strategies that are the highest priority for maintaining the region’s forests’ ability to mitigate climate change:

1.      Keep forests as forests! Continuing and increasing land conservation efforts are necessary to minimize the on-going loss of forest to development. Clearing forests for other uses not only releases much of the existing stored carbon but also eliminates all future potential for sequestration. 

2.      Ensure that forests are managed sustainably and remain carbon sinks at the landscape scale (including carbon stored in harvested wood products). When forests become a net source of carbon to the atmosphere, they become part of the problem rather than part of the solution. 

There are many public and private organizations and programs working on these strategies, though increasing the pace and capacity of these programs is imperative.

We acquired a lot more that looks like this…

This is a long-term restoration project!

AMC’s management is aimed at the long-term restoration of this young, heavily-harvested forest to a more mature, higher-carbon, more natural forest across our ownership through a combination of reserves and conservative timber management. In addition to the ecological and carbon benefits, we also seek to improve the timber quality of the forest, so that future harvests will have a higher proportion of sawlogs (and consequently a greater storage of carbon in durable wood products). 

About 28% of our land is permanently set aside as ecological reserves and another 14% is designated as no-harvest protection zones. These include steep slopes (inoperable), riparian buffers, forested wetlands, and “retention areas”. The latter are areas of up to several hundred acres that are reserved from harvesting to protect areas of particularly high value such as older forest or scenically sensitive areas. These areas will continue to sequester carbon at natural rates, likely for a century or more. 

About 4% of our land is nonforested or developed (primarily in roads and three traditional sporting camps), leaving about 54% available for timber management.

AMC has conducted timber harvests every year since 2004 on our first property, the Katahdin Iron Works (acquired in 2003). 

The Roach Ponds property (acquired in 2010) had very low stocking due to very heavy harvesting by the previous owners, and we did not begin timber harvests there until 2017. Timber management under AMC ownership is just beginning on the Pleasant River Headwaters Forest, acquired in 2022.

The interactive map at the end of this story provides the opportunity to take a closer look at AMC's management zones and timber harvests, and to see how the forest has changed under AMC's ownership.

In the early years, the highest priority on the Katahdin Iron Works property was on salvaging beech that were severely infected with beech bark disease (more formally, beech scale–Nectria complex, an introduced fungus that is spread by an insect). These were often two-storied stands (similar to the earlier example) with a high proportion of beech and generally low timber quality due to past high-grading (or “take the best and leave the rest”). 

Typical commercial management would be a complete overstory removal, leaving a young even-aged stand. However, while removing diseased beech, low-value trees, and short-lived species (white birch, aspen, and balsam fir), we put a high priority on leaving a residual overstory.

In this early harvest, mature yellow birch were retained over an understory of young trees 10 to 20 feet tall.

In this 2007 harvest, yellow birch and red spruce were retained.

Some of these retained trees may be harvested in the future, while others will be left to live out their full life, becoming a source for large old trees and eventually large dead wood.

As a result of the low quality of these stands and our focus on retaining good quality trees for future growth, nearly 90% of the harvest in our first five years consisted of hardwood pulpwood, used for making paper but not suitable for sawing into lumber.

Candidates for overstory retention included:

• Higher value or longer-lived species (primarily sugar maple, yellow birch, and red spruce).
• All white pine, which is limited on our properties but which is projected to be a future "climate change winner".
• Good growing stock (well-formed trees of desirable species) (below).
• Trees at least 18" in diameter (lower left).
• Standing dead trees ("snags") (upper left).
• Rotten or cavity trees that have high value for wildlife (lower right).
• Healthy beech, which are likely to be resistant to the disease (upper right).

Some retained overstory trees will eventually become large “supercanopy” trees, and after that large dead wood. In addition to being significant carbon reservoirs, these biological legacies are critical habitat for a wide range of species, not only mammals, birds and amphibians but also the insects, mosses, lichens, and fungi that carry out the physical and chemical processes of wood decay and soil building. (E.O. Wilson called these the species “that hold the world steady.”) These legacies are particularly important in maintaining these species and functions in younger forests following heavy disturbance. They essentially serve as “biodiversity lifeboats”.

As we progressed to harvesting in better-quality stands (which are more limited in extent), harvesting used a combination of thinning and first entry shelterwood to maintain a mature overstory while promoting growth on the highest value trees and developing or releasing regeneration. This involves removing lower value trees – a “leave the best and take the rest” approach that is the mirror image of high-grading. Even in these better quality stands, hardwood pulp comprised about two-thirds of the harvest volume.

This first entry shelterwood in a high-quality hardwood stand was conducted in 2016.

This multi-aged stand with a good amount of white pine was thinned in 2010. This stand will be managed to maintain this uneven-aged condition while creating openings to regenerate white pine.

AMC's approach to continuous overstory retention can be seen in this image of the Benson Mountain region. Most of the lower two-thirds of the area in the photo has been harvested under AMC ownership. The upper-slope spruce-fir forest at the top of the photo is either inoperable or has been set aside as a retention area.

Having some amount of young early-successional forest in the landscape is important for species that depend on that habitat. AMC does not specifically manage for larger areas of young forest as this habitat is plentiful on the surrounding commercial ownerships, but will reconsider this policy if conditions change in the future.

Restoration harvesting also includes the removal of plantations of species not native to their site. These plantations have very low biodiversity value.

This 62-acre low-quality 35-year-old red pine plantation within the Roach Ponds Ecological Reserve had about 50% of the trees removed in 2016, opening space for natural regeneration. The remainder of the stand will be removed once regeneration is well-established. This type of one-time restoration harvesting is allowed under the terms of our “forever wild” easement on the Roach Ponds reserve in order to speed up the return of the reserve to a more natural condition.

An emerging focus of AMC management is “early intervention silviculture”. AMC’s timber management area contains many thousands of acres of young even-aged stands resulting from past clearcuts or overstory removal harvests. These include softwood stands (both planted and naturally regenerated) established after the widespread clearcutting during the spruce budworm epidemic of the 1970s and 1980s, many of which received herbicide treatments and precommercial thinnings by previous landonwers, as well as hardwood and mixed stands that have not been treated since they were established.

These extensive young stands can be seen in this 2009 image from the central Roach Ponds property. The largest outlined stands are nearly 100 acres in size.

Commercial thinning of young spruce-fir stands is a common practice among many landowners. These stands can be harvested as soon as the trees reach commercial size (about 6” diameter). This treatment not only promotes more rapid growth in the residual trees, but also reduces carbon emissions from the stand. If these stands were left to naturally “self-thin”, the carbon in the trees that die would return to the atmosphere through decomposition in a couple of decades. If the trees are harvested in a thinning, some of the carbon in the removed trees will remain stored in the manufactured lumber for a much longer time.

AMC has also begun precommercial thinning of younger spruce-fir stands, which is generally done when the trees are less than 10’ tall.

This 45-year-old even-aged post-clearcut stand contained a good species mix. A light first entry commercial thinning removed short-lived species (white birch and aspen) and lower-value trees while giving more growing space to good growing stock of higher-value species (sugar maple, yellow birch, white pine and red spruce).

Precommercial thinning of young hardwood stands is not a common practice. In these stands, AMC has begun crop tree release treatments. Potential crop trees of desirable species with good form are identified and marked, and competing trees around the crop tree are cut. This leaves the crowns of the crop trees free to expand and increases the rate of carbon sequestration on the most vigorous trees, but at a lower cost than thinning the entire stand.

Loss of carbon from decomposition of the litter layer and soil organic matter is increased when the soil is disturbed and exposed to greater heating. AMC minimizes this impact by the use of processer/forwarder harvesting systems, also known as “cut to length”. In this system, the harvester (processor) uses a complex cutting head to cut the tree, strip the limbs in the woods, and cut the stem into logs. The forwarder then picks up the logs and carries them to the road. This system allows the equipment to travel over a protective carpet of logging slash, and logs (or whole trees) are never dragged along the ground. This system also reduces the productive acreage lost to skid trails and landings.

For over a decade AMC has been working to restore aquatic connectivity on our property by removing culverts and restoring natural stream channels.  Where roads will remain in use the culverts are replaced with bridges. This not only allows for fish passage that was previously blocked, but also makes the road system more resilient in the face of increasingly severe storms.

To date AMC has carried out over 100 culvert removal projects, reconnecting nearly 100 miles of headwater streams to their downstream river systems. See  Finding Success in the Forest - AMC's Fish Habitat Restoration Project   for more information.

How are we doing? 

Inventories of our timber management area in 2010 and 2020 provide a picture of how the forest has changed under AMC’s management. Over this time we harvested about 97% of our modeled allowable harvest on the Katahdin Iron Works (KIW) property, but only 30% on the Roach Ponds (RP). 

All measures of forest maturity (basal area*, timber and sawtimber volume, number of large trees) increased 10% to 30% between 2010 and 2020. Proportionately these increases were greater on the Roach Ponds property due to the limited amount of harvesting, though the absolute values still trail the Katahdin Iron Works property.

*"Basal area" is the total cross-sectional area of tree stems at a height of 4.5 feet above the ground. It is a useful measure of how dense a stand is, since it is independent of the size of the trees (i.e., a lot of small trees may have the same total basal area as fewer large trees.)

On-site carbon stocking in our timber management area is estimated to have increased about 17% over 10 years, though the levels remain lower than in our Katahdin Iron Works (KIW) and Silver Lake (SL) ecological reserves. These figures do not include long-term carbon storage in the wood harvested from the managed lands.

What does the future hold? 

Forest managers use computer models to project a forest’s growth into the future, and to calculate the sustainable harvest level given whatever constraints a landowner choses to impose. For AMC, these constraints include limits on clearcutting and overstory removals and a requirement to maintain a certain level of mature forest at all times. The model was run for a period of 50 years, though it will be redone every 10 years following new inventories. 

AMC’s model shows that we will be harvesting significantly less than growth for the next 40 years. As a result, timber stocking (and carbon storage) in our timber management area should increase, from about 17 cords/acre in 2020 to about 27 cords/acre in 2065. Carbon stocking in our reserves and other no-harvest areas should increase even more.

Over the same time, the higher stocking will also support increasing harvest levels, with the allowable harvest nearly doubling over this period. Eventually we will reach a point where we are able to sustainably harvest at a level equal to growth while maintaining high timber stocking and carbon storage.  

This may seem like a case of having your cake and eating it too.  However, it’s better to think about it as an example of the benefits of deferred gratification. Foregoing harvesting to build up on-the-ground stocking allows for both higher stocking and higher harvests in the future, but only after a period of reduced harvests compared to what a financially optimal model would provide. This approach comes at a cost in the form of reduced near-term revenue, which is why commercial landowners have been reluctant to adopt this approach.  

However, there is a way to reduce the financial impediments to implementing this type of Group B management. Enter forest carbon offset markets!

Carbon offsets 

At the most basic level, a carbon offset is an action taken by one party that reduces greenhouse gases in order to balance the emissions of another party, who pays the first party for the offset. Offsets can either remove carbon from the atmosphere (as with forest growth) or prevent its release (as with methane capture). The universal unit of offset credits is 1 metric ton of carbon dioxide (or its equivalent for other greenhouse gasses). 

There is broad consensus on the basic criteria required for a credible offset project. The claimed emissions reductions must be real, additional, permanent, verifiable, and enforceable. “Additionality” means that the emissions reductions must be above and beyond what would have happened without the project, otherwise known as “business as usual”. Offset registries are the bodies that develop detailed protocols for quantifying and verifying offset credits, and who track the ownership and retirement of credits.

There are many different kinds of offsets, including methane capture from landfills, mines, and agricultural feedlots; increasing carbon storage in agricultural or wetland soils; reducing emissions from industrial processes; and renewable energy. Improved Forest Management (IFM) projects are focused on retaining and increasing carbon storage in forests by changing management practices – exactly what AMC is doing. In the United States, the primary registries for IFM projects are the Climate Action Reserve (CAR) and the American Carbon Registry (ACR).

In 2022 AMC adopted its  Net Zero Strategic Plan , which sets forth the goals and strategies that will guide AMC’s efforts in this ambitious initiative. 

The Plan includes two major commitments: to compile and publicly report our greenhouse gas emissions each year, and to utilize the Carbon Mitigation Hierarchy as our basic approach to reaching net zero. 

The Carbon Mitigation Hierarchy is a widely-adopted three-step strategy for moving towards net zero that prioritizes real emissions reductions. It includes:

1. Avoiding and reducing emissions from fossil fuels in transportation and buildings through energy efficiency, conservation, and electrification.
2. Eliminating emissions from electricity by investing in renewable sources of energy (both on-site and purchased).
3. Using carbon offset credits to balance remaining emissions, which cannot be (or have not yet been) eliminated. 

Ideally, both gross emissions and the use of offsets to balance these emissions should decline over time.

The primary source of emissions from AMC’s operations is the burning of fossil fuels at our facilities for heating, hot water and cooking (“Scope 1 – buildings”). AMC’s emissions have averaged around 1,500 metric tonnes of CO ₂  since 2010. Emissions actually increased over this period – while we have become more efficient we have also grown, adding new facilities and more staff. 

In contrast, the Katahdin Iron Works Ecological Reserve carbon project by itself (comprising just 10% of AMC’s ownership) is sequestering at least 10 times that much carbon each year, and is generating more than enough offset credits to balance AMC’s annual emissions several times over.  

Does this mean AMC has already reached net zero? If we just retire (rather than sell) sufficient credits, are we done?