By Brent Sohngen (sohngen.1@osu.edu)

A recent study argued that tree harvesting all over the world – including fuelwood harvesting in the world’s poorest places – cause large unaccounted carbon emissions (see Peng et al., 2023). Many people have taken issue with the approach used in Peng et al. because the calculations ignore history, the future, and markets, among other things (see this blog post). The question of whether wood harvesting creates a net carbon emission, and thus whether wood products are “sustainable”, has been well-studied, with hundreds of analyses. Much of this analysis seems to focus on the life cycle of wood harvested in rotational forestry operations in developed places like the United States, Canada, and Europe.

What about the substantially less intensive harvesting that happens all over the tropics where relatively few stems per hectare are removed in each operation? There is lots of worry that this wood harvesting can lead to considerable emissions because of the damage done to nearby forests when large, old trees are removed or when roads are built to skid trees out of the forest (Ellis et al., 2019; Matricardi et al., 2020). Do these types of harvests lead to net carbon emissions for the earth?

This question came to the forefront a few years ago when a group proposed that the pedestrian promenade on the Brooklyn Bridge be restored with wooden planks from a tropical forest in northern Guatemala (see https://www.brooklynbridgeforest.com/about). The tropical forest where harvesting would happen wasn’t just any tropical forest, it was a forest managed by the community of Uaxactun. Most people have never heard of this small and isolated community in the northern reaches of Guatemala. More than a hundred years ago, however, community members there helped the Wrigley Company become a household name in the United States by providing the essential ingredient for Juicy Fruit – chicle latex from a local tree species. Tapping trees to provide latex was (and is) a sustainable operation, much like harvesting maple syrup in North America. By the second half of the twentieth century harvests were waning as easier to obtain substitutes displaced chicle. Fortunately, the roots of sustainably managing forests in the region were well established.

The question facing New Yorkers today worried about the sustainability of their future promenade is not as straightforward as harvesting sap from trees. Instead, the question of sustainability revolves around whether removing trees from this ecosystem can be done sustainably at all. Studies like Peng et al. are declarative, stating bluntly that any harvesting creates massive carbon emissions equaling 1 ton CO2 per m3 of wood removed. To put this in context for the average American homeowner with a 2500 square foot (230 m²) house, your abode probably contains around 35 m³ of timber. The standard claim is that you are storing 32 tons of CO₂ in that wood, all while the same forest used to grow those trees is, with near 100% certainty, removing those and more tons from the atmosphere every year.

In contrast, the claim by Peng et al. is that the 2500 ft² wood-framed house created an unabated emission of 35 tons of CO₂ when built. Under the social cost of carbon estimates used by the Biden administration, the Peng et al. result means that every homeowner today should pay a one-time tax of about $2 per ft² for their wooden homes to make up for the extensive damage they have apparently done to the atmosphere. I bet you, like me, never thought you were living with such a large climate liability?

Harvesting is much different in Guatemala than the typical operation in the United States where these calculations are based. In Uaxactun, the typical wood harvesting operation results in removing only a few really valuable stems per hectare every 30 years or so. Such harvesting operations undoubtedly lead to carbon emissions, even if some of the stem wood ultimately makes its way into wood planks fastened to the Brooklyn Bridge. These emissions happen when cut wood is left in the forest to decompose slowly over time. Sawdust and small bits will litter the floor of the local mill, perhaps making their way into bedding for animals or other uses. In the forest, it will take some time for the gap in the canopy to be closed by growth of new trees and for the carbon in the forest stock to be regenerated.

Emissions definitely happen when wood is harvested in Uaxactun. The question is whether those emissions are replaced by re-growth in the forest. If you cut 1 ton CO₂ of trees out of the forest, put 0.3 tons in long-lived wood products, and emit the other 0.7 tons that looks like a lot of emissions. However, if 1 ton regrows over the next decade or two, society has 1 ton in the forest, and 0.3 tons of CO₂ stored in wood products for a total of 1.3 tons stored.

Studies like Peng et al. use a no-harvesting counterfactual and discounting to calculate that this time when the forest has less carbon after harvesting creates a carbon deficit for the atmosphere. By ignoring economics, and focusing entirely on physical calculations, this approach conveniently ignores the likelihood that if Uaxactun’s forests are no managed for timber, they are likely to be converted to agriculture – a far worse counterfactual than the old growth forest Peng et al. assume. In this part of the world, harvesting wood provides economic opportunity for families and communities, which helps the groups who manage forests repel the forces of land conversion. This benefit of timber harvesting is not an idle promise in the Peten. It’s the result of really good planning and incredibly hard work over the last 30+ years.

During Guatemala’s long civil war, which ended in 1996, the Peten, as the region in northern Guatemala is known, served as a relief valve of sorts for people displaced by violence. As population grew in the 1980s and 1990s, worry that rampant agricultural conversion would imperil biodiversity and cultural artifacts from previous Maya civilization grew.

In the 1990s, Guatemala and its international partners set about on a bold plan to create the Maya Biosphere Reserve, an area that would be managed partly as a park, but more importantly as a practical place where land and its forests could be used for the betterment of people and the planet. Some of the forests were indeed devoted to national parks and protected areas. But large tracts were also devolved communities where timber and non-timber forest product harvesting could benefit residents. Other parts of the forest were left to their fate in a buffer zone.

Over time, forests in national parks and protected areas have fared poorly throughout large swaths of the Maya Biosphere Reserve (Blackman, 2015) as drug lords and others have used land as they wish. These forests are owned by government, which doesn’t do a lot to ward off the interlopers. So too, forests have been lost in the buffer zone where ordinary people have converted them to farms. The forests in the community concessions, however, have fared pretty well, especially in communities like Uaxactun, which have a long-established connection to the region (Bocci et al., 2018; Fortmann et al., 2017).

It turns out that when local residents are given access to land they can call their own, and make money from the products the land provides, they will protect it. There is a good bit of tourism in the area with Guatemalans and foreigners alike showing considerable interest in Maya history, but tourism has not yet developed at a scale anything like that in Costa Rica. Perhaps if tourism achieved such a level of remuneration, timber harvesting would not be necessary, but today, timber harvesting in places like Uaxactun provide much needed income that generates carbon benefits timber harvesting and by avoiding deforestation.

Among other problems (see earlier blog post), studies like Peng et al. miss this important function of tree harvesting. There are absolutely poorly planned and executed tree harvests all over the world. Tree harvesting in many old growth situations undoubtedly does lead to net emissions that may not be recovered by forest regrowth and wood product storage. Yet in some of those tropical forests in places like Uaxactun, tree cutting is an economic activity that keeps carbon in forests rather than the atmosphere, all while providing benefits to the communities and owners who cut trees, giving them a livelihood that will encourage them to protect the very forests they manage.

Blackman, A., 2015. Strict versus mixed-use protected areas: Guatemala’s Maya Biosphere Reserve. Ecol. Econ. 112, 14–24.

Bocci, C., Fortmann, L., Sohngen, B., Milian, B., 2018. The impact of community forest concessions on income: an analysis of communities in the Maya Biosphere Reserve. World Dev. 107, 10–21.

Ellis, E.A., Montero, S.A., Gómez, I.U.H., Montero, J.A.R., Ellis, P.W., Rodríguez-Ward, D., Reyes, P.B., Putz, F.E., 2019. Reduced-impact logging practices reduce forest disturbance and carbon emissions in community managed forests on the Yucatán Peninsula, Mexico. For. Ecol. Manag. 437, 396–410.

Fortmann, L., Sohngen, B., Southgate, D., 2017. Assessing the role of group heterogeneity in community forest concessions in Guatemala’s Maya Biosphere Reserve. Land Econ. 93, 503–526.

Matricardi, E.A.T., Skole, D.L., Costa, O.B., Pedlowski, M.A., Samek, J.H., Miguel, E.P., 2020. Long-term forest degradation surpasses deforestation in the Brazilian Amazon. Science 369, 1378–1382.

Peng, L., Searchinger, T.D., Zionts, J., Waite, R., 2023. The carbon costs of global wood harvests. Nature 1–6.

By Brent Sohngen (sohngen.1@osu.edu)

For nearly 25 years, carbon offsets in agriculture and forestry have been the next big thing – a market with huge potential to increase revenue for farming with certain practices like conservation or no till, cover crops, the Conservation Reserve Program (CRP), or even growing trees. There is power in an idea that remains relevant for that long, but prices for carbon stored in American farms and forests remain too low to make it much of a “thing” at all. To most farmers, carbon offsets are just an annoyance – and a vivid reminder that the very people who tell us a “carbon crisis” is upon us are not serious at all about solving the problem.

The question I most often hear farmers ask is “why are carbon prices offered to farmers so low?” It’s a legitimate question. The news these days often contains reports of unexplained weather events, like heavy rainfall, that scientists claim have been caused by climate change. If there really is a crisis and farmers can help by doing something different, why is the price so low?

Some people are willing to pay a lot of course. Californians are willing to pay $30 per ton to stop emissions from factories. People in other parts of the world, like Europe or New Zealand, will pay more than twice that to stop emissions.

However, nature-based offsets – the ones farmers and foresters produce – garner only $1 per ton. If I were a farmer, I’d view this paltry amount as a slap in the face. Here I’ll try to explain why it’s not.

The most important reason why prices for nature-based offsets are so low is they exist nearly exclusively in a voluntary market. Needless to say, this is exactly how farmers and their farm organizations want these markets to be structured. They definitely do not want regulated carbon markets to enter farms directly.  Even in California – the most regulated state in the U.S. – most farmers only see the effects of the California cap and trade system indirectly, that is, through their input prices. California farmers face high carbon prices when they buy things like gasoline, diesel, and other chemicals that are manufactured under the California cap and trade system, but they do not pay directly for carbon emissions from their farms. Further, like other farmers in the U.S., they receive a pittance for most carbon they store in their farm fields or forests.

Elsewhere in the U.S., farmers do not face much indirect regulation of their carbon, so they just see the low price offered for nature-based storage. It is too bad the price is low, but it is low precisely because the system we have in the US is the voluntary carbon market that farmers have demanded since people first started talking about carbon markets 25 some years ago.

To see what we’re missing here in the U.S., consider the case of New Zealand. There, farms and forests can be opted into the regulated carbon market and thus receive the much higher regulated carbon price for their nature-based carbon storage. Once opted in, however, farmers must pay for any emissions they create. So if they plant trees and get rewarded as those trees grow, they will face a stiff penalty if they harvest the trees. Despite this “tax,” which only hits if the trees are harvested, the economics tilts heavily in favor of planting trees in New Zealand.

It is no surprise, then, that when nature-based carbon storage is worth the same amount as carbon emissions – as it is in New Zealand – landowners are planting lots of trees on their farmed land (primarily their grazing lands).

In the rest of the world, including the U.S., study after study shows that if farms were to face a regulated carbon price, the economics would tilt in favor of growing trees rather than traditional farming. Growing trees is a lot easier, and with European, California, or New Zealand level prices (>$30 per ton CO2), growing trees would be more valuable than farming in many places where it currently is not.

In the U.S., a voluntary market benefits farmers and farm organizations by keeping land from converting to conservation and carbon storage. A higher regulated carbon price would benefit a slice of farmland owners because it would raise the value of their land asset. However, farm renters and farm organizations would suffer because more land would be devoted to trees and less to farming. It turns out that low carbon prices are pretty much exactly what the doctor ordered for much of the farming community.

Additionality matters, too

Other factors, like additionality, also contribute to low carbon prices for nature-based carbon. Additionality is the concept that carbon sequestration in forests or agriculture should only count if the carbon was placed there because someone paid for the carbon and not something else. It is hard to tell, however, if carbon prices are low because lots of nature-based carbon already in the market is non-additional, or if non-additional carbon results from low carbon prices. This is a real conundrum.

Consider this, the Norwegians ran around for 10 to 15 years paying rather paltry amounts (<$5/ton) for avoided deforestation in low-income countries. As a result, some people tried to pass off non-additional carbon to get the low sum of money Norway was offering. Go figure, eh? One has to ask if that’s evidence of actual cheating or straightforward rational economic behavior? After all, if you are paying me nothing why would I give you something?

Causality, however, also runs the other way. Farmers who have long done conservation tillage provide free carbon storage to society because they privately benefit for other reasons.  Forest owners whose trees contribute to the nearly 800 million tons of forest-based sequestration in the United States every year, provide an even bigger service for free – worth nearly $100 billion per year at EPA’s current estimate of the damage of each ton causes.  Yet neither type of landowner could ever be compensated on private markets because their efforts would not be considered additional.

Following UN Framework Convention on Climate Change (UNFCCC – a treaty the US signed and ratified in the early 1990s) guidelines, the U.S. government treats the 800 million tons in the forest carbon sink as additional and adjusts its expectations of other industries accordingly. That’s right, automobile fuel efficiency standards, regulations on power plants, subsidies through the Inflation Reduction Act, and all other federal rules on carbons emissions are set assuming foresters and farmers keep doing their part. This means that all these other rules are less stringent than otherwise because farmers and foresters (mostly foresters) are so good at storing carbon on the landscape for free.

This non-additional carbon actually is worth billions to companies that are regulated, yet the farmers and foresters get no credit, and see no benefit.

Worries about additionality have created some credence problems for offset markets too. Newspapers love to write about failures in the private offset market, making failure seem like the norm rather than the outlier it is. Worries born of this reporting for sure reduce demand for nature-based offsets.

For example, the Science Based Targets Initiative (SBTi) has encouraged private companies to make pledges to reduce their carbon emissions by 50% within 10 years. Until recently, however, they were susceptible to the news-driven hype about the non-additionality of most forest-based carbon offsets, so they would not allow companies to use offsets when meeting their “science-based” targets. This, of course, was an odd stance because the science of carbon removal by offsets is clear. SBTi recently seems to have shifted their approach to allow companies some flexibility in meeting their targets with offsets.

Over time, SBTi’s change could increase demand and raise offset prices, especially if it signals a broader embrace of offsets within the voluntary carbon market.

In conclusion, there are three primary reasons why nature-based carbon prices are so low. One reason is that the suppliers – farmers and foresters – want carbon offsets to remain voluntary. Prices in voluntary markets will always be lower than prices in regulated markets. This is the most important reason.

The other two reasons relate to additionality. First, foresters and farmers are so proficient at providing massive amounts of carbon storage for free, they have driven down the price of carbon. Second, worries about getting caught with some of this non-additional carbon lower demand.

Unfortunately, it won’t be easy to solve any of these problems, meaning nature-based carbon prices are likely to remain low for the foreseeable future.  The recent decision by SBTi to finally admit that carbon offsets were also science-based and allow them to be used by companies trying to meet stringent targets, however, could provide a demand boost for the nature-based market. So far, we haven’t seen a significant change, but this could change in the future.

Many of us in the forestry community were saddened to learn of the passing of Darius Adams back in December, 2023. The news was especially sober given that Darius and his colleague Richard Haynes, along with Joseph Buongiorno, had just won the Marcus Wallenberg prize – the premier award in the field of forestry.

It would be hard to overestimate the impact Darius had on the world of forestry economics. The TAMM model, which Darius developed with Richard Haynes, showed us how to model timber demand and supply in multiple markets, accounting for trade between the regions (Adams and Haynes 1980).  Rather than treating prices as exogenous, Darius and Richard figured out how to make prices endogenous.

Endogenous prices were a real innovation. The U.S. Forest Service had a long history of using “gap” models to predict the gap between harvesting and growth.  These models had no prices.  They just calculated the gap between expected demand for industrial wood and supply. Supply was based on expected growth using historical biological conditions. If more demand was expected, the gap between supply and demand would widen. Consumption wouldn’t moderate if prices rose because there were no prices.  Supply was static.

In markets, of course, there is no gap. If demand increases but supply doesn’t, prices increase, and vice-versa. Gap models had some pretty serious negative side effects, one of which was they validated Forest Service efforts to harvest too much timber. Worry over a looming timber famine propelled Teddy Roosevelt to create national forests and later led to the 1920 Capper Report and the 1933 Copeland Report. Both decried the poor state of private forest management in the United States, but the Copeland report was the most forceful about solutions, proposing that private land either be regulated more heavily or brought into the public domain (Clapp 1934).

Fortunately, those recommendations weren’t followed, but worry about the diminished state of US forest stocks was embedded in everything the U.S. Forest Service did. In the second half of the twentieth century, forest stocks were on the rise in the United States, yet the gap models consistently predicted too few forests would be available for rising demand (Clawson 1979). They motivated a national need for more timber harvesting in federal forests.

Of course, timber prices did rise over the twentieth century, the inevitable consequence of rising demand combined with old growth depletion (Berck 1979). Higher prices also spurred people to plant forests on private land starting in earnest the 1940s. Gap models missed that.

TAMM changed the conversation from gaps to markets and scenarios, providing policy makers with a much needed tool to evaluate the potential consequences of their policy decisions before they set the policy in motion.  The timing of TAMM couldn’t have been better. In May, 1991, Judge Dwyer blocked Forest Service timber sales in the Northwest, setting into motion one of the great supply shocks of the last century – a 15% reduction in wood supply, a 62% increase in timber prices, and massive new demand for southern pine and Canadian lumber (Wear and Murray 2004). Lots of other things were happening at the same time, including the softwood lumber dispute with Canada followed by a massive building boom in the United States during the 1990s.

Economic models do not solve problems, but they do help people better understand them.  They also help policy makers better understand how their decisions will affect market outcomes. That’s what TAMM did best. And when turbulent times hit the American wood economy in the 1990s, TAMM helped policy makers make better decisions, through reports for the Resource Planning Act (RPA) Assessment every 10 years and various other reports and papers.

If TAMM was all Darius did, it would have been enough. Along the way, however, Darius recognized one of the limitations of TAMM on the supply side. Foresters, you see, can adapt to changing market conditions in lots of ways, one of which is by changing the age at which trees are harvested. If prices are rising, for example, foresters can slowly extend rotation ages and increase the supply of wood from many intensively managed forests.

Furthermore, the tree planting revolution had been underway for decades, yet models like TAMM assumed tree planting was exogenous. Surely landowners were responding to prices not just by how they harvested trees, but also in where and when they planted them.  Darius needed a way to make the age of tree harvesting and the area and intensity of forest planting in the US endogenous.

He and others managed to do this with a nifty new model developed in the late 1990s called FASOM. The FASOM developers had many good economists involved, but Darius left an unmistakable imprint on the forest sector components of this model. Today the model is widely used for policy analysis, in particular by the US Environmental Protection Agency to analyze critical policies that affect forests and forest management in the United States.

I knew Darius mostly through his writings and associates, although we did have a number of opportunities to interact over the years. His writings, about prices, timber markets, timber market modeling, and policy analysis were always filled with great insights. The economics world has moved on a bit from models like the ones Darius developed – to simple econometric approaches focused on identifying a causal relationship. However, complex structural models like the ones he developed still play a critical role by providing policy makers with all-important insights. As much as the academics amongst us are determined to look forward and devise new techniques and methods, sometimes it’s useful too to look back too.

Adams, Darius M., and Richard W. Haynes. 1980. “The 1980 Softwood Timber Assessment Market Model: Structure, Projections, and Policy Simulations.” Forest Science 26 (suppl_1): a0001-z0001.

Berck, Peter. 1979. “The Economics of Timber: A Renewable Resource in the Long Run.” The Bell Journal of Economics, 447–62.

Clapp, Earle H. 1934. “Major Proposals of the Copeland Report.” Journal of Forestry 32 (2): 174–95.

Clawson, Marion. 1979. “Forests in the Long Sweep of American History.” Science 204 (4398): 1168–74.

Wear, David N., and Brian C. Murray. 2004. “Federal Timber Restrictions, Interregional Spillovers, and the Impact on US Softwood Markets.” Journal of Environmental Economics and Management 47 (2): 307–30.

Why global wood harvests aren’t emitting 3.5 to 4.2 Gt CO₂ per year in net emissions.

Brent Sohngen (sohngen.1@osu.edu)

Part I: Good modeling matters, bad modeling matters more.

A recent article by Peng et al. (2023) called “The carbon cost of global wood harvests” published July 5, 2023 in Nature, suggested that economic models are not up to the task of measuring carbon emissions from wood product harvesting. The authors of that study calculate that wood harvesting will cause a net emission of 3.5 to 4.2 Gt CO_­2­ per year over a 40-year period from 2010 and 2050. The authors claim to estimate this value from a counterfactual that assumes no harvesting at all. This supposed counterfactual is calculated via a biophysical model that compares the carbon flux after harvest in a regenerated stand plus the market products with the stand left alone.

The authors propose an interesting idea – comparing a world with timber harvests to a world without timber harvests – but their approach and model makes no sense. Peng et al. model 40 years of future timber harvests with a biophysical model (called the CHARM model) that uses only per capita income to determine how much timber gets harvested every year, what type of timber gets harvested every year and where it gets harvested. That’s right, they are modeling a market, but dispensing with the economics because, in their words, economic models are not “credible.” There are no costs to harvest wood in the model, no interest rates that affect investments or rotation ages, no equilibrium conditions, no setting of prices equal to marginal cost, no investments in new stocks, etc. They acknowledge economics is hard, so they ignore it, and instead deploy a set of arbitrary rules to consume wood, harvest trees, and regenerate trees.

Not surprisingly, their key result that there are 3.5 to 4.2 Gt CO₂ in net emissions from wood harvesting is ridiculous.

Not surprisingly, this is not the first time this type of modeling has been deployed. After its creation in the early 1900s, the United States Forest Service famously started chasing a quixotic timber famine for much of the twentieth century. As shown by Clawson (1979), study after study by the US Forest Service found that US forests were growing far less than was needed for future timber harvests. In response to these “gap” models, which also ignored economics, the Forest Service created a huge timber harvesting operation that eventually met 15 % of the nation’s wood supply with federal timber – much of it old growth.

Thankfully, Darius Adams and Richard Haynes, who won the Marcus Wallenberg Prize in forestry this year, created an actual economic model to project timber harvests, prices, and forest stocks (Adams and Haynes 1980). They changed the dynamic. Whole posts could be written on the timber famine and its effects on US forest policy, but the upshot for the CHARM model is that most of us thought the idea of using purely physical models like this to predict future timber harvesting and forest growth were a thing of the past. But if we have learned anything from one of the most famous purely physical modeling exercises in the past –”The Limits to Growth” effort by Donnela Meadows and others in 1972 (Meadows et al. 1972) – purely physical modeling is quite the allure.

Part II: A closer look at the big numbers in Peng et al

(Hint: keep track of gross and net here)

It is incredibly unlikely that future timber harvesting would lead to net emissions of CO₂ from forests of 3.5 to 4.2 Gt CO₂ per year as claimed in Peng et al. Right now, land use, land use change, and forestry are a net global sink of 6.6 Gt CO₂ per year (Nabuurs et al. 2022). Gross emissions from timber harvesting and deforestation are about 5.9 Gt CO₂ per year, meaning forests and other land uses are pulling 12.5 Gt CO₂ per year from the atmosphere in gross. Most of the gross emission is deforestation. Gross emissions from industrial wood production estimated by the Global Timber Model are about 1.6 GtCO₂ this decade.

The Peng et al. study does include global wood fuel consumption, which we do not include in GTM.  Wood fuel is nearly half of all wood consumption globally, and its consumption is skewed heavily towards developing regions. We haven’t included it in GTM because it’s hard to know how much of this wood came from the scraps of timber cuttings, or deforestation. But the IPCC numbers above do include it.

So, here is a scorecard so far:

IPCC Gross emissions from all wood harvesting and deforestation                =             5.9 Gt CO₂/yr

GTM estimated gross emissions from industrial wood harvesting                 =             1.6 Gt CO₂/yr  

Potential gross emissions from wood fuel and deforestation                         =             4.3 Gt CO₂/yr  

Gross emissions are rather large. But Peng et al. claim net emissions from just timber harvesting (not deforestation) are as big or bigger. How do they get to their rather large calculation of 3.5 to 4.2 Gt CO₂ per year?

First, they ignore economics and construct a purely biophysical model. This will result in overestimating harvests and underestimating regrowth because the model will not harvest efficiently and will not regenerate efficiently. Seriously, have a look at Marion Clawson’s Science article in 1979. Dr. Clawson’s colleague at Resources For the Future, Roger Sedjo, got it right when he declared at a 1980 meeting at the International Institute for Applied Systems Analysis in Vienna, Austria:

“Many observers anticipate a growing scarcity of wood through the remainder of this century and into the next accompanied by an attendant rise in the relative price of wood products and the primary forest resource. Given these expectations it is certainly prudent to investigate the potential of plantation forests in meeting future demand and to recognize that the possibility of higher future real stumpage prices may provide incentives for forestry investments not previously economically justifiable.”

The idea that we are running out of trees and people will incompetently just watch it happen has been around a long time, but it is far from reality.  Today we get more than 40% of our wood consumption from plantations, of which there are over 130 million hectares globally (Mishra et al. 2021; McEwan et al. 2020; FAO 2020). People have responded to higher prices by planting trees as an investment. These trees suck up carbon and do it before the tree is harvested. They are not perfect environmentally, but they are renewable, as is the forestry sector as a whole (Mendelsohn and Sohngen 2019).

Biophysical models have no way to capture the behavioral response of landowners to market signals, like rising prices, so they ignore it. This means they get harvesting and regenerating wrong – by lots.

Second, the Peng et al. article is just an implementation of the incorrect argument by Searchinger et al. (2009) that emissions from timber harvesting and burning should be double counted. Favero, Daigneault, and Sohngen (2020) and recently Li, Sohngen, and Tian (2022) showed in different ways that Searchinger’s argument is wrong. Double counting emissions, in contradiction to the correct approach by IPCC, leads to less not more forests, just like higher taxes lead to less production of the good taxed. Peng et al. create a calculation of carbon emissions from harvesting which, they hope, will allow the emissions to then be counted a second time.

Third, Peng et al are making a normative judgment about which tons to count. They have a strange accounting procedure that starts counting gross emissions and gross sequestration at the time of the timber harvest rather than at the initial period in the model run. So they have decided to ignore the growth in forests that happens before trees are cut. Since a large (>40%), and growing, portion of wood cut by industrial markets is dependent on plantations planted for future harvesting, why not count this growth before the harvest? The reason is that this growth would negate a lot of the negative effect Peng et al. calculate, so they make a normative decision to ignore tree growth before harvesting. This convention is different from every other forest sector model.

Fourth, their approach to discounting is just strange. They use a mixture of positive discounting and no discounting together, in the same calculation. I don’t know what to make of that. I guess in the post-truth era, scientists now can do whatever they want. But their discounting amplifies their results and ignores how markets respond to changes in interest rates. So with this strange (also normative) approach, they get a bigger result.

Fifth, their counterfactual is unrealistic, and not just because it assumes no harvesting of wood. It’s weird because if they used an economic model, the carbon implications wouldn’t be so simple to calculate. There is a whole discussion out there about leakage when people stop harvesting trees to store carbon, and it has been around for quite a while (Murray, McCarl, and Lee 2004; Sohngen and Brown 2004). How can anyone do a scenario of no harvesting of wood without considering the market response?

Dave Wear and Brian Murray famously showed what happened when timber harvesting was stopped in federal forests in the United States (Wear and Murray 2004). For those who don’t want to read this really good paper, the short story is that they show the assumptions Peng et al make that you can evaluate the carbon consequences of a no harvest scenario by just looking at the site where you stopped logging are completely false. Peng et al. may try to argue that Wear and Murray is just a model result, so not real, but Wear and Murray is an empirical result, with real data and good statistics. Those of us who develop models of the forest sector create our models so that the same types of equilibrium conditions Wear and Murray rely on are met in our models. Peng et al. seem unaware of any of this, ignore links between timber stands over time and space, and ignore market equilibrium.

There are other problems with Peng et al., of course, but the ones above are the bigger ones. No doubt, the press will continue loving what Peng et al. estimate because it sounds big and problematic, when it’s just a restatement of an earlier incorrect argument. Hopefully, though, in the policy arena, real science will prevail.

References

Adams, Darius M., and Richard W. Haynes. 1980. “The 1980 Softwood Timber Assessment Market Model: Structure, Projections, and Policy Simulations.” Forest Science 26 (suppl_1): a0001-z0001.

Clawson, Marion. 1979. “Forests in the Long Sweep of American History.” Science 204 (4398): 1168–74.

FAO. 2020. “Global Forest Resources Assessment 2020 Main Report.” Rome: United Nations Food and Agricultural Organization. https://doi.org/10.4060/ca9825en.

Favero, Alice, Adam Daigneault, and Brent Sohngen. 2020. “Forests: Carbon Sequestration, Biomass Energy, or Both?” Science Advances 6: eaay6792.

Li, Rong, Brent Sohngen, and Xiaohui Tian. 2022. “Efficiency of Forest Carbon Policies at Intensive and Extensive Margins.” American Journal of Agricultural Economics 104 (4): 1243–67.

McEwan, Andrew, Enrico Marchi, Raffaele Spinelli, and Michal Brink. 2020. “Past, Present and Future of Industrial Plantation Forestry and Implication on Future Timber Harvesting Technology.” Journal of Forestry Research 31: 339–51.

Meadows, Donnela, Dennis L Meadows, Jorgen Randers, and William W Behrens III. 1972. The Limits to Growth. New York: Signet.

Mendelsohn, Robert, and Brent Sohngen. 2019. “The Net Carbon Emissions from Historic Land Use and Land Use Change.” Journal of Forest Economics 34 (2).

Mishra, Abhijeet, Florian Humpenöder, Jan Philipp Dietrich, Benjamin Leon Bodirsky, Brent Sohngen, Christopher PO Reyer, Hermann Lotze-Campen, and Alexander Popp. 2021. “Estimating Global Land System Impacts of Timber Plantations Using MAgPIE 4.3. 5.” Geoscientific Model Development 14 (10): 6467–94.

Murray, Brian C., Bruce A. McCarl, and Heng-Chi Lee. 2004. “Estimating Leakage from Forest Carbon Sequestration Programs.” Land Economics 80 (1): 109–24.

Nabuurs, GJ, R Mrabet, AA Hatab, M Bustamante, H Clark, P Havlik, J House, et al. 2022. “Agriculture, Forest and Other Land Uses (AFOLU).” In Climate Change 2022: Mitigation of Climate Change. Vol. Sixth Assessment Report. Intergovernmental Panel on Climate Change Working Group III. https://www.ipcc.ch/assessment-report/ar6/.

Searchinger, Timothy D., Steven P. Hamburg, Jerry Melillo, William Chameides, Petr Havlik, Daniel M. Kammen, Gene E. Likens, Ruben N. Lubowski, Michael Obersteiner, and Michael Oppenheimer. 2009. “Fixing a Critical Climate Accounting Error.” Science 326 (5952): 527–28.

Sohngen, Brent, and Sandra Brown. 2004. “Measuring Leakage from Carbon Projects in Open Economies: A Stop Timber Harvesting Project in Bolivia as a Case Study.” Canadian Journal of Forest Research 34 (4): 829–39. https://doi.org/10.1139/x03-249.

Wear, David N., and Brian C. Murray. 2004. “Federal Timber Restrictions, Interregional Spillovers, and the Impact on US Softwood Markets.” Journal of Environmental Economics and Management 47 (2): 307–30.

This page hosts code, working papers, and lists of published papers developed with the Global Timber Model.  The Global Timber Model is a dynamic optimization model of global forests, used for analysis of policy questions.  Code for various papers will be deposited here and is freely available for use.  If you have questions, please contact Brent Sohngen (sohngen.1@osu.edu).