By Mitch Lansky
To meet the Paris Agreement goal of limiting global warming to 1.5 degrees Celsius, countries that are major carbon dioxide sources will have to greatly reduce the majority of their fossil-fuel carbon emissions in just a few decades. Many scientists have concluded, however, that emission reductions are not enough. Carbon dioxide can linger in the atmosphere for centuries. There is already enough carbon in the atmosphere so that climate instability has already started — the symptoms being an increase in the size, frequency, and intensity of storms, floods, droughts, and fires, as well as glacial melting.
It is highly unlikely that the Paris Agreement goals can be met unless there is a massive effort to take carbon out of the atmosphere and store it — in addition to drastically reducing emissions. This combination of reduced emissions and increased sequestration and storage should become part of a double bottom line approach to prevent increasing climate disruption.
So far, economically viable technologies that are effective at removing carbon dioxide (CO2) emissions without creating more air pollution problems are more a hope for the future rather than a reality for today. If the capture and storage technologies were viable now, they would already be used extensively to allow continued burning of both fossil fuels and biomass.
There are, however, natural ways to remove CO2 from the atmosphere that can be cost-effective and, in addition to reducing atmospheric carbon, can benefit biodiversity, water quality, and recreation. Expanding the area and volume of forests is one of the most promising of such natural climate solutions.
Trees, through photosynthesis, take in carbon dioxide and convert it to sugars, cellulose, lignins and other carbon-based substances, while emitting oxygen as a “waste product.” Wood, after all the moisture is removed by drying, is half carbon by weight. The more wood there is in a forest, the more carbon there is in a forest. The more carbon there is in a forest, the less there is in the atmosphere.
Carbon is found in “pools” that include live trees (above and below ground), dead trees, the forest floor, and the forest soil. Soil carbon makes up nearly half of all forest ecosystem carbon when the majority of trees are younger. As trees get bigger and older, and live-tree volumes increase, the live-tree carbon pool eventually surpasses forest soil as a site of carbon storage.
There are two basic approaches to increasing forest and carbon volume — passive and active. “Passive” refers to treating a forest as a reserve or “wilderness,” in which there is little or no cutting. Trees are allowed to get as big as they want and even to die. “Active” refers to attempts to manage the forest, usually for forest products, in a way that also increases the average volume per acre over time. Society has to decide how to balance these two strategies over the landscape.
William Moomaw (professor emeritus, Tufts) has pointed out that the best way to increase carbon storage immediately is to grow more volume on existing trees, rather than wait until planted trees mature. He calls this passive strategy “proforestation.”
Maine, which has the highest percentage of forestland of any state, has great potential (for reasons that I will discuss later) to have a positive climate impact with not only passive, but also active management, if landowners follow the principles, goals, guidelines, and standards from low-impact forestry (LIF).
Impact of LIF Goals on Carbon Capture and Storage
What follows are some of these LIF guidelines and how they can help landowners reach their carbon goals:
Choose the least disturbing silvicultural system that is appropriate for the species and site. “Least disturbing” is determined by choosing a system that minimizes the size, intensity, and frequency of openings and impacts. For example, a whole-tree harvest is more intensive than a tree-length harvest, which is more intensive than a shortwood (cut-to-length) harvesting system. Large openings are more disturbing than group removals, which are more disturbing than individual tree removals that leave windfirm residuals. For even-aged systems, short rotations (50 to 80 years) are more disturbing than longer rotations (over 100 years). Frequent entries for uneven-aged systems are more disturbing than longer return cycles.
By such guidelines, the most disturbing system would be whole-tree clearcuts (removing tops and branches as well as boles) on short rotations. Such systems have a period of negative Net Ecosystem Productivity (NEP), meaning the site emits more carbon than it sequesters, for 10 to 15 years or more.
According to a report on managing forests for carbon in New England, “This loss of carbon from decomposition is enhanced when large openings are created in the forest, which increases soil temperature and moisture availability and hence microbial activity.”
The period of net emissions could take up 1/4th of short rotations, or 1/4th of the land area in even-aged management. A study from Oregon concluded that forestry/logging was the biggest single source of carbon emissions in that state.
The least disturbing approach would be light selection cutting that leaves enough residual to reach a relatively closed canopy in 10 or 15 years (known as cutting to the “B-Line”). This is what European scientists call “continuous cover forestry.” Such a system leads to uneven-aged forests. Multi-canopied forests can store more carbon per acre than single-canopied forests.
Sometimes the condition of the site is so dominated by poor-quality, short-lived trees that such silviculture is not practical, in which case the manager can try variations of group selection or irregular shelterwood, where there is partial retention of more than one age class.
The average forest volume per acre is determined by adding tree volumes of all acres, including forest stands that have just been cut, and dividing by the number of acres. The more forest residual that is left behind and the more that residual is allowed to grow before it is cut again, the higher the overall average carbon volume will be in the forest landscape.
Cut less than growth. Cutting more than growth (“overcutting”) is not sustainable over the long run.Cutting less than growth over a rolling 10-year period would lead to an increase in volume, over time, of live trees. Cutting less than growth can also be seen as an investment in the future forest and can lead to bigger average diameters and more dead-wood habitat. Growing wood fast does not lead to increased volumes over the landscape if one is cutting the wood as fast or faster than it grows.
Establish a pecking order that favors retention of a diverse forest with longer-lived, higher-quality trees. The “pecking order” refers to which trees to target first for cutting. For the LIF approach to management, this preference would be for cutting the shorter-lived, lower-quality trees first. Cutting the highest-quality, longer-lived trees and leaving the poorest-quality, shorter-lived trees is called “highgrading.” Dominance by short-lived trees could lead to shorter disturbance cycles (caused by wind, insects, or rot) and thus lower future average volumes per acre. Longer-lived tree species in Maine can continue to capture and store carbon for centuries. Maintaining a diversity of species and sizes suitable to the site can contribute to higher stand stability (increased resistance to disturbance and increased resilience from disturbance).
Manage to increase average tree diameter over time. Bigger, older trees have more fungal partners (mycorrhizae) that contribute increased water and nutrients to the tree in exchange for carbon sugars given to the fungi from tree roots. Five percent to more than 20% of carbon captured by tree photosynthesis gets passed on to these mycorrhizal fungi, which can be a major source of soil carbon.
Bigger trees, with more foliage, more height, and bigger diameters, capture and store more carbon than smaller trees. One strategy for increasing average diameter is to focus cutting on slow-growing, suppressed trees to encourage growth on larger-diameter dominant trees. These larger trees are already more windfirm, with better root systems. In contrast, cutting the big trees and leaving small trees is a form of diameter-limit cutting that degrades a stand over time.
Manage for structural complexity. Big old trees, dead standing trees, dead down trees, and uneven-aged forests are important biological legacies associated with late successional forests. Dead trees still store carbon, long after they stop capturing it. Having an abundance of green trees as well as dead trees means more carbon storage than with just green trees alone. And dead standing and down trees are important wildlife habitats and so enhance biodiversity.
Leave well-stocked residuals. Leaving less than optimal distribution of trees is called “understocking.” Full stocking (“A-Line”) is when the foliage of one tree merges with the foliage of neighboring trees. It is full use of the growing space. Forest productivity is greater if, after a cut, the residual forest can reach full stocking in 10 or 15 years (“B-Line”), compared to heavy cutting that leaves a residual that is below the “C-Line,” or too sparse to reach full stocking unless or until the regeneration grows into the canopy, which might take decades.
Minimize area in trails and yards. Some mechanized harvesting systems require around 25% of the forest to be in trails and yards to accommodate mechanical harvesters. By using cables or animal power, lower-impact systems can operate with narrower trails spaced further apart (thereby allowing crown closure over the trails). If trails are 150 feet apart and 75 feet of cable is used to winch logs to the trail, less than 7% of the area overall would be in trail.
If a mechanized logger cuts 25% of the trees for trails and 25% of what remains, that will leave only 56% (0.75 x 0.75) of the original stocking. If a LIF logger removes 7% of the stand for trails and 25% of what is left, that would leave behind 70% (0.75 x 0.93) of the original stand, which is 25% more than the residual of the mechanical logger. Thus, the LIF logger will leave a better-stocked, more productive residual.
Minimize damage to residual trees. Damage to residual trees can lower productivity, increase susceptibility to insects or diseases, and lower log value. Healthy, undamaged trees grow better, live longer, and capture and store more carbon.
Minimize damage to soil and tree roots. Soil compaction and rutting can lead to more erosion and standing water, less soil oxygen (and less healthy soils), and less tree growth (and less carbon sequestration), and lower valued trees. The LIF preference is to cut when ground is frozen or dry and stable.
Potential for Improvements
A recent study documented that more than 40% of timberlands in northern New England are occupied by degraded and/or understocked stands. Just leaving more adequate stocking, according to this study, could increase carbon storage by 20%, and this would increase even more if management favored less-damage-prone, longer-lived species.
Due to decades of overcutting, northern Maine counties, where forest management is dominated by industrial-scale logging, have barely more than half the volume per acre of forests in southern Maine counties. For example, Washington, Aroostook, and Somerset Counties (northern and eastern counties) all have (as of 2018, according to USDA Forest Service data) less than 16 cords to the acre. In contrast, more southerly counties, Androscoggin, Lincoln, and Sagadahoc, have 30 cords to the acre.
More than 1/3 of the forest landscapes in Aroostook, Piscataquis, and Somerset Counties are dominated by seedlings and saplings. Much of the young growth is dominated by shorter-lived species, such as balsam fir and red maple.
Duveneck and Thompson (2019) looked at current versus potential carbon storage in the northern New England forest landscape. Fully 68% of the reduction of potential forest carbon storage in the region is due to “harvest regimes on corporate-owned lands.”
Landowners that have been contributing to the trends of forest degradation in these counties are responding more to short-term economic incentives than long-term carbon or biodiversity values. The state lacks basic silvicultural-based regulations, or even guidelines for management plans under Tree Growth Tax Law, to encourage landowners to avoid overcutting, understocking, or highgrading.
While the result of these trends in degradation have created great potential for increasing forest carbon storage, the political/economic context that allowed such forestry to be socially and legally acceptable is still in force.
Even if landowners are inspired to manage for increased carbon capture and storage, this strategy for offsetting fossil fuel-based carbon emissions is time-limited. Forests cannot perpetually increase in volume to make up for carbon emissions of a growing economy. At some point society will have to come to terms with the need to live within limits. In the short term, however, there is lots of room for improvement.
Markets and Carbon
One approach to managing for reducing carbon emissions has been to advocate for expansion or creation of markets that substitute wood for fossil fuels or for concrete or steel building materials. The logic here is that wood is “renewable” and thus all uses must be “green.” This addendum is focused on the forest management side of the equation rather than the forest products’ emissions side of the equation, but it is fair to mention that:
- Expanding markets in a context where overcutting is legal and acceptable could lead to more overcutting over the coming decades as markets increase.
- Biomass emits more carbon dioxide per unit of electricity than coal. Reducing carbon sequestration by cutting more wood per acre and increasing carbon emissions by burning wood inefficiently does not seem like a winning climate strategy.
- Only 35% (as of 2018) of what gets cut in Maine is used for sawlogs, the rest gets chipped and either pulped or burned. When landowners cut for sawlogs, they normally also sell what is not suitable for sawlogs to pulp or biomass markets, most of which release the carbon in these products in the relative short term.
- The majority of the volume of trees cut for lumber ends up as logging waste (including roots, tops, and branches), chips, slabs, edgings, planer shavings, and sawdust that are either abandoned to rot, are burned, or get pulped rather than being manufactured into lumber that is stored in buildings for the long term. The landowner is thus sending a much higher percentage of cut-tree volume to short-lived products rather than to long-lived products.
- Even if a landowner tries to avoid markets that supply short-term wood uses that get converted to carbon dioxide, this does not get rid of those markets. Wood will “leak” from other properties, regions, or countries to fill the demand. Since climate change is a global issue, such “leakage” can lessen or eliminate the well-meaning efforts of such forest landowners.
Companies, such as BP, Chevron, Koch Industries, J.P. Morgan, BlackRock, and Disney, have paid large woodland owners money for carbon credits and get to claim they are on the way to “net carbon zero.” In return, these large landowners get an income stream that they could use to improve management or to fund more conservation programs. Smaller woodlot owners would like access to that income stream, too. In 2020, Amazon pledged $10 million in carbon credits to encourage carbon sequestration in family forests in the Appalachian region.
On the surface, these arrangements seem to be a win/win for carbon emitters and for landowners. For these payments to actually make a difference in the climate, however, the following hurdles must be overcome:
- Permanence. The changes must be good for a century or more; otherwise, someone could pocket the compensation money for achieving some stocking goal and then, a few years later, cut the forest. There also has to be a good likelihood that the entities making the payments and monitoring the results on the ground are going to last far into the future.
- Leakage. Discussed earlier, the standing volume gains in the forest, which are getting payments, cannot be countered by standing volume losses for other landowners who are capturing the market share lost from the compensated lands.
- Additionality. The payments cannot be just to support business as usual. The payments must be for forestry practices that would not have happened if it were not for the payments. If landowners get payments to continue managing as they would have if they were not paid, then there will be little change in carbon storage over the landscape.
- Cost effectiveness. The payments should be competitive with other expenditures to reduce carbon-dioxide emissions to ensure that society is getting the best bang for the buck.
- Timeliness. The benefits should start in the short term, not get worse in the short term with the promise of improvement many decades from now (which is the promise of biomass electricity generation). Climate instability has already started and must be addressed ASAP.
- Externalities. The forest practices should benefit multiple forest values, such as water quality, biodiversity, and/or recreation, rather than harm them. In other words, there should be a preponderance of positive externalities (side effects of commercial activities that are not reflected in the market value of the products), rather than negative.
- Measurable goals. The forestry goals need to be clear and measurable, and there also need to be standards in place that actually achieve the stated goals.
- Scalability. The offset programs need be large enough by themselves or in combination to actually make a difference in stored carbon over time.
- Exclusivity. The carbon “saved” should not be claimed by more than one entity.
Even when one considers carbon storage of harvested wood products, studies have concluded that passive management stores more carbon than the combination of carbon in managed stands plus the carbon stored in wood products. A recent study of 60 years of management at the Penobscot Experimental Forest, in Bradley, Maine, found that the uncut “control” had 52% more total carbon per acre than managed forests, even when accounting for harvested wood products.
Passive forest carbon management, however, also has hurdles to overcome. The most serious hurdle is “leakage” — that other landowners in other areas will cut more heavily to meet the market demands that the reserved lands are no longer supplying. The solution to this problem is not to have less reserved lands, but to have more demand reduction. Americans, who account for 4% of the world’s population, are consuming 21% of the world’s sawn wood and 26% of the world’s pulpwood.. There is great opportunity to cut waste and inefficiency before needing to cut more trees.
While climate change is a global issue, it is harder to see the connection between local actions and global consequences with the climate than with, for example, wildlife habitat. We are impacted not only by what happens in Maine forests, but also by what happens in the Amazonian, African, and Southeast Asian rainforests. And what happens in the great boreal forests of Canada and Russia. And what happens due to large industries and sprawling cities. It is easy to feel overwhelmed by the scale of the problem. Still, we have a responsibility to take care, if we can, of our local forests on a stand, county and state level. As Theodore Roosevelt said, “Do what you can, with what you have, where you are.”