Savanna carbon: great plains?

Savanna Carbon

Savanna carbon is stored in an open mix of trees, brush and grasses. Savannas comprise up to 20% of the world’s land, 30% of its annual CO2 fixation, and we estimate their active management could abate 1GTpa of CO2 at low cost. This 17-page research note was inspired by exploring some wild savannas and thus draws on photos, observation, anecdotes, technical papers.


Savannas landscapes are summarized on pages 2-4, following some on-the-ground exploration of these landscapes near Kruger National Park in 2022, which made us take a deeper interest in savanna carbon.

As a result, we are re-thinking three conclusions about nature and climate, as part of our roadmap to net zero:

(1) Conservation is as important as reforestation and should not be dismissed. Once slow-growing trees and endangered species are lost, they are not coming back (pages 5-7).

(2) Optimization of CO2 is particularly nuanced in savanna landscapes and must be balanced with other environment goals, especially biodiversity (pages 8-11). This is especially true for fire suppression (pages 12-14). Learning curves are crucial (pages 11, 15).

(3) Re-wilding pasturelands into savannas may absorb 50–100 tons of CO2 per acre. This is less than forests. But it may be more achievable in certain climates. And where it attracts tourist revenues, CO2 abatement costs may actually be sub-zero (pages 14-16).

Our conclusions and CO2 quantifications of savanna carbon are summarized on page 17.

Underlying data into the CO2 absorption of tree species and savanna landscapes is tabulated here. As an approximate breakdown, 33% of the CO2 is stored in soils, 33% in living woody tissue, and the remainder is distributed across roots, dead wood, shrubs and litter.

Wood use: what CO2 credentials?

Wood use CO2 impacts

The carbon credentials of wood are not black-and-white. They depend on context. So this 13-page note, focusing on wood use CO2 impacts, draws out the numbers and five key conclusions. They highlight climate negatives for deforestation, climate positives for using waste wood and wood materials (with some debate around paper), and very strong climate positives for natural gas.


The CO2 accumulation profile of a forest is set out on pages 2-3. For example, a mature forest absorbs 90% less net CO2 each year than a young forest. This is our baseline for assessing carbon counterfactuals, and numbers can be flexed in our underlying data-file.

Deforestation has net climate negatives across the board. It even emits 35% less CO2 to burn coal (i.e., forests that have been dead for 100M years) than to cut down and burn living forests (page 4).

Conversely, gathering waste wood that has fallen to the forest floor and would otherwise decompose is ‘climate positive’ across every category that we assessed, with other hidden climate benefits (page 5).

Wood materials are the best use of wood, as each ton of sustainably harvested timber avoids 0.5 – 1.2 tons of net CO2 versus using other industrial materials. The note explores how wood product and chemicals companies might benefit from this theme, although paper is an exception and much more debatable (page 6-8).

Wood fuels are still used remarkably widely. But the carbon in lignin and cellulose is already part oxidized, so there is less energy “left to release” as it is converted to CO2. Whereas natural gas derives c54% of its energy release from hydrogen atoms converting to innocuous water vapor. This means each MTpa of LNG can displace an astonishing 10MTpa of CO2 where it prevents the burning of wood from deforestation (pages 9-11).

Biomass power can make sense in some contexts, but only when the wood is sustainably sourced, clearly substitutes coal and helps diversify energy sources/security (page 12).

Our key conclusions and implications for decision-makers are provided on page 13.

Finnish forests: a two billion ton CO2 case-study?

Finland forests CO2 removals

Can forestry remove CO2 from the atmosphere at multi-GTpa scale? This 19-page note about Finland forests CO2 removals is a case study , where detailed data goes back a century. 70% of the country is forest. It is managed sustainably, equitably, economically. And forests have sequestered 2GT of CO2 in the past century, offsetting two-thirds of the country’s fossil emissions.


Nature-based carbon removals underpin 25% of all the decarbonization in our roadmap to net zero. The key debate is whether they can scale to this level, measurably, reliably, as covered on pages 2-3.

Finland makes for an excellent case study. An overview of the country, its forests and its forest-centric culture is set out on pages 4-6.

The structure of Finnish forestry is broken down on pages 7-10. Our data are aggregated from Natural Resources Institute Finland, and offer the best, most comprehensive breakdown we have ever encountered on the costs of forest management (across 20 line items), harvesting practices and realized pricing for different categories of wood.

Carbon credentials are calculated on pages 11-12, explaining the maths above: 2GT of CO2 sequestered in the past century, versus 3GT of nationwide fossil emissions.

Productivity data are also excellent, improving at 1% per year over the past century, with biomass yields per hectare almost doubling since the first half of the 20th century. This is mainly through improved forestry practices (pages 13-16).

Conclusions of Finland forests CO2 removals are spelled out on pages 17-19. 110 countries, with 5bn acres of land, have a 1-5x better environment for growing forests than icy Finland. For Brazil, for example, to get repeatedly ‘trounced’ by Finland should be as surprising in forestry as it would be in soccer.

To read more of our outlook on Finland’s forestry product business that aspires to be a leading provider of renewable products, please see our article here.

Sitka spruce: our top ten facts?

sitka spruce benefits

Sitka spruce is a fast-growing conifer, which now dominates UK forestry, and sequesters CO2 up to 2x faster than mixed broadleaves. It can absorb 6-10 tons of net CO2 per acre per year, at Yield Classes 16-30+, on 40 year rotations. This short note lays out our top ten conclusions; including benefits, drawbacks and implications.


(1) Origins. Sitka spruce trees (Picea sitchensis) were first found in Baranof Island, in the Gulf of Alaska, in 1792, by Scottish Botanist Archibald Menzies. They was first brought to Europe in 1831, by another Scottish botanist, David Douglas (namesake of the Douglas fir). And they were named Sitka, after the headquarters of the Russian-Alaskan fur trade, which was the main reason Europeans were exploring the region at the time.

(2) Commercial Forestry Areas. In the UK, Sitka now comprises 30-60% of forest areas, following extensive planting since the 1970s (estimates vary). Likewise, in Ireland’s forests, Sitka Spruce represents 50-75% of all carbon stored and 90% of all wood harvested, across 300,000 hectares planted. Sitka is also grown to a lesser extent in Denmark, Iceland, France and Norway (although the latter now considers it invasive and is trying to phase it back).

(3) Growing Conditions. Sitka spruce naturally extend from Alaska down into Northern California, but seldom >200km inland or above 1,000m altitude. It is demanding of air and soil moisture, therefore grows best in temperate rainforests, coastal fog-belts or river-stream flood plains. It is also surprisingly light-demanding for a spruce, whereas one of the main advantages of Norwegian spruce in the forestry projects we are evaluating is that it is shade-tolerant, and can thus grow in below a pine canopy, adding carbon density. As usual, the right tree needs to be matched to the right climate to maximize CO2 removals (note below).

(4) Tree Sizes. Sitka is the tallest-growing spruce species in the world, usually reaching 45-60m height. Yet the world record is 96m. This is huge. The world’s largest Norwegian spruce (Picea abies) on record has reached 62m (in Slovenia), and the largest pine (Pinus sylvestris) is 47m (a 210-year old specimen in Southern Estonia). Sitka is the fifth largest tree in the world, behind usual suspects such as Giant Sequoia, where the tallest tree on record has reached 116m.

(5) Carbon Credentials. In Scotland, Sitka usually grows at 16-22 m3/ha/yr. In forestry, it is common to refer to a tree stand’s peak ‘Mean Annual Increment’ in m3/ha/year as its Yield Class. So 16-22 m3/ha/year would translate into Yield Class 16-22. In turn, the UK’s Woodland Carbon Code publishes excellent data for computing CO2 sequestration from yield classes (here). Yield classes 16-22 would translate into 6-8 tons of CO2 sequestration per acre per year.

sitka spruce benefits

(6) Even Higher Yield Classes have been reported by foresters growing Sitka, however, in the range of 30-45. For example, one source states that in Ireland Sitka yields can reach “34 tonnes per hectare per year of stem wood”, which would translate into a yield class in the 40-70 range. Some plots have reported the largest individual trees adding a full m3 of wood each year, which might translate into yield classes 50-100. But let’s not get carried away. It is not too difficult to translate yield class into CO2 uptake. For example, we would typically assume 450kg/m3 density for spruce, 50% of which is carbon. Each kg of elemental carbon is equivalent to 3.7 tons of CO2, and maybe 80% of absorbed CO2 can be prevented from returning to the atmosphere over the long run (note here, model here). This yields the chart below, suggesting 10 tons of CO2 removal per year at Yield Class 30.

sitka spruce benefits

(7) Carbon Comparisons. Sitka spruce has been called 2x as effective at carbon removals as traditional broadleaf woodland. Again, data from the UK Woodland Carbon Code would seem to bear this out, positing 4-6 tons of CO2 sequestration per acre per year for mixed broadleaves in their typical yield classes 4-8 (chart below). This matters because we tend to assume 5 tons of CO2 removal per acre per year for reforestation projects our roadmap to net zero.

sitka spruce benefits

(8). Commercial Forestry Practices. Underpinning our assumptions above for Sitka spruce are relatively dense plantings, at 1.5 – 2.0m spacings, which will translate into an extremely dense 1,000-1,800 trees per acre, grown over a 40-year rotation. Our numbers are averaged across thinned and unthinned stands, although the latter absorb 50% more CO2. This might all deflate the cost of a typical forestry project (including land purchase costs) from $40/ton CO2 pricing to around $25-30/ton CO2 pricing, while also lowering land requirements, which also matters for CO2 removals (notes and models below).

(9) Timber Uses. Sitka’s wood is light, strong and flexible, with a dry density around 450kg/m3. For comparison, hardwoods like oak are more typically 750kg/m3. Hence the Wright brothers’ Flyer was built using Sitka spruce, as it made the world’s first powered flight in 1903. In WWII the British even used it instead of aluminium to produce parts of the de Havilland DH.98 Mosquito military aircraft. Products derived from spruce range from packaging materials to construction timber. We think this presents an opportunity in the materials space, including in Cross Laminated Timber, where spruce is the most commonly used input material…

(10) Biodiversity Drawbacks. Biodiversity versus CO2 removal is always going to require trade-offs. A mono-culture Sitka spruce plantation will clearly be less bio-diverse than mixed broadleaf, but certainly more biodiverse than a Direct Air Capture plant. Overall, Sitka-heavy forests seem to be OK at promoting biodiversity. In America’s North-West, Sitka naturally grows alongside Western hemlock, Western re-cedar, Yellow cedar, mosses, horsetails, blueberries and ferns. In the spring, new growth can be eaten by mammals; while in the winter, needles can comprise up to 90% of the diet of bird species such as blue grouse.

Our conclusion for decision-makers is that Sitka spruce will help to accelerate prospects for nature-based carbon removals in the energy transition, creating direct opportunities in the forestry value chain, through to indirect opportunities in equities (notes below).

On a personal note, for the reforestation projects that we are undertaking in Estonia, we are mostly considering bio-diverse mixes with a backbone of pine and spruce. Attempts to grow Sitka in Estonia are more chequered. A 120-year old stand has reached 36m average height on the Island of Hiiumaa. This implies the ability to achieve 3,000m3/ha timber density, which is around 2.5x Norwegian spruce. However, other attempts to grow Sitka in Estonia have had mixed results, especially away from the Coast. So I would like to incorporate some Sitka in my plans here, but I am just not sure I can rely on them in this climate.

Nature based CO2 removals: theory of evolution?

Learning curves and cost deflation are widely assumed in new energies but overlooked for nature-based CO2 removals. This 15-page note finds the CO2 uptake of reforestation projects could double again from here. Support for NBS has already stepped up sharply in 2021. Beneficiaries include the supply chain and leading projects.


Nature based carbon removals are re-capped on page 2, covering their important, their costs and how they are re-shaping the energy transition.

But policy support is growing faster than expected, as outlined on pages 3-5. Now that nature-based CO2 removals are on the map, they are in competition with other new energies. Hence which technologies will ‘improve fastest’?

The historical precedent from agriculture is that yields have improved 4-7x over 50-100 years, due to learning curve effects. So will forestry practices be similar? (pages 6-7).

Thirty variables can be optimized when re-foresting a degraded eco-system. We run through the most important examples on pages 8-13.

But is optimizing nature ‘natural’? This is a philosophical question. Our own perspectives and conclusions are offered on page 14-15.

Reforestation: a real-life roadmap?

This 12-page note sets out an early-stage ambition for Thunder Said Energy to reforest former farmland in Estonia, producing high-quality CO2 credits in a biodiverse forest. The primary purpose would be to stress-test nature-based carbon removals in our roadmap to net zero, and understand the bottlenecks. IRRs can also surpass 10% at $35-50/ton CO2.


The correct way to structure a reforestation project is one of the most important questions in the energy transition, but few seem to have cracked the code. This is our conclusion from hundreds of models and discussions, which are summarized on pages 2-4.

Our own interests in undertaking a reforestation project are set out on 5-8, combining personal circumstances, economics and an aspiration to understand the reforestation process in more detail.

What will a high-quality project need to look like? Our expectations and goals are set out on pages 9-12. As transparently as possible. This is a structured list of questions, and our initial hypotheses, to be addressed in future research.

Carbon negative construction: the case for mass timber?

Cross laminated timber costs in carbon negative construction

The construction industry accounts for 10% of global CO2, mainly due to cement and steel. But mass timber could become a dominant new material for the 21st century, lowering emissions 15-80% at no incremental costs. Debatably mass timber is carbon negative if combined with sustainable forestry. This could disrupt global construction. This 17-page note outlines the opportunity and who benefits.


CO2 emissions of the construction industry are disaggregated on pages 2-3. Some options have been proposed to lower CO2 intensity, but most are costly.

Sustainable forestry also needs an outlet, as argued on pages 4-7. Younger forests grow more quickly, whereas mature forests re-release more CO2 back into the atmosphere.

The case for cross-laminated timber (CLT) is outlined on pages 9-11, describing the material, how it is made, its benefits, its drawbacks, and its CO2 credentials.

CLT removes CO2 at no incremental cost, illustrated with specific case studies and cost-breakdowns on pages 12-13.

CLT economics are attractive. We estimate 20% IRRs are achievable for new CLT production facilities on page 14.

Leading companies are described on pages 15-16, including large listed companies, through to private-equity backed firms and growth stage firms.

Our conclusion is that CLT could disrupt concrete and steel in construction, helping to eliminate 1-5GTpa of CO2 emissions by mid-century.

Bio-engineer plants to absorb more CO2?

Our roadmap towards ‘net zero’ requires 20-30GTpa of carbon offsets using nature based solutions, including reforestation and soil carbon. This short note considers whether the task could be facilitated by bio-engineering plants to sequester more CO2. We find exciting ambitions, and promising pilots, but the space is not yet investable.


What is bio-engineering? In 2016, scientists at DuPont gene-edited maize to grow more effectively in dry conditions. In 2017, researchers at the University of Oxford introduced a maize gene into rice plants, to increase the number of photosynthetic chloroplasts surrounding leaf veins. In 2019, scientists at Huazhong Agricultural University gene-edited rice to tolerate higher soil salinity. These are examples of bio-engineering: modifying the genetic code of plants for practical purposes.

How could it help? The world’s land plants absorb 123GTpa of carbon each year through photosynthesis. 120GTpa is re-released through respiration and decomposition. The result is a net sink of 3GTpa. For contrast, total anthropogenic carbon emissions are 12GTpa. It follows that small changes in the natural carbon cycle could materially shift carbon balances, per our climate model below.

The limitations of photosynthesis. Photosynthesis uses sunlight to convert CO2 into plant-sugars. It is only 1-5% inefficient, suggesting great potential for improvement. It is also vastly complex, comprising over 170 separate sub-stages. Amidst the complexity, RuBisCO is the most crucial limitation.

The limitations of RuBisCO. RuBisCO is an enzyme that catalyzes the reaction between CO2 and RuBP during photosynthesis. However, the RuBisCO enzyme is imprecise. It evolved at a time when the world’s atmosphere contained much lower oxygen concentrations. Unfortunately, under present atmospheric conditions, 20-35% of RuBisCO’s catalytic activity reacts O2 with RuBP, instead of CO2. The resultant products cannot continue their biochemical journey into becoming sugars. Instead, they are broken down in the process of photorespiration. Photorespiration uses up c30% of the total energy fixed by photosynthesis, and re-releases CO2 into the atmosphere. Photorespiration lowers agricultural yields by 20-40%.

What if RuBisCO could be helped to fix more CO2 and less oxygen? One way to do this is to increase the atmospheric concentration of CO2 in greenhouses, which can increase crop yields by c30%, per our note below. Another way is through bio-engineering.

Realizing Increased Photosynthetic Efficiency (RIPE) is a research institute funded by the Bill and Melinda Gates Foundation, UK foreign aid, the USDA and academic institutions. It aims to generate higher crop yields per unit of land, using bioscience. After ten years of research, RIPE has recently modified tobacco plants with genes from green algae and pumpkin plants to reduce the energy penalties from photorespiration. The result is that these modified tobacco plants grew 40% larger. A follow-up study may achieve plants that are 60% larger. Similar modifications are also being tested on soybeans and cowpea plants.

Researchers at the University of Wurzburg have also modelled metabolic pathways that may increase the photosynthetic efficiency of plants, potentially by as much as 5x, with results published in 2020. The work uses synthetic CO2-fixating carboxylases, RuBisCO from cyanobacteria, and additional methods of preventing fixed CO2 from being re-released. Experiments are planned to test the work in tobacco plants and thale cress.

Increasing photosynthetic efficiency and crop yields could be a crucial help, lowering the land intensity of crop production, which covers 1.7bn hectares of the globe today (data below). For comparison, our target of 15GTpa of reforestation will require 1.2bn hectares of land, hence any material reductions in cropland requirements will be helpful.

Sequestering more of the CO2. 50-95% of the carbon that is stored in natural eco-systems is not stored in biomass above ground, but in the soil. An emerging set of agricultural practices that restore soil carbon are explored in our research note below. But another option is to ‘program’ plants to grow deeper, larger roots, which push more carbon into soils.

The Land Institute in Salina, Kansas has developed a grain called Kernza. It is derived from an ancestor of wheat. It is perennial, rather than requiring yearly replanting. Its roots reach 3-6x further into the soil than conventional wheat, which connotes 3-6x more carbon storage, and also promotes drought resistance. It is being grown across 2,000 acres today.

The US Department of Energy also has a Laboratory of Environmental Molecular Sciences, aiming to increase carbon transfer into the soil. One team has developed a strain of rice that emits less methane, as it contains a gene from barley, reducing the carbon that the plant moves underground, which in turn reduces the carbon that can be metabolized by anaerobic bacteria. Studies are underway to reverse the process and increase the carbon that crops move underground.

The Salk Institute for Biological Studies is based in La Jolla, California. It is undertaking the most elaborate program to bioengineer crops and other plants, to sequester up to 20x more CO2 than conventional crops. Deploying these plants across 6% of the world’s agricultural lands are said to potentially offset 50% of global CO2 emissions.

Salk’s Harnessing Plants Initiative started in 2017 and aims to grow “ideal plants” with greater efficiency at pulling CO2 from the air, deeper roots that store more carbon underground, and other superior agricultural properties. One pathway is to promote production of suberin, the carbon-rich polymer in cork (but also found in melon rinds, avocado skins and plant roots). This is a waxy, water-resistant compound that degrades very slowly, thus remaining in the soil for centuries.

In 2019, Salk’s team discovered a gene, which determines whether roots will grow shallow or deep. It is called EXOCYST70A3, and affects the distribution of the PIN4 protein. PIN4 modulates the transport of auxin, a hormone that regulates root architecture. Different alleles of EXOCYST70A3 can increase root depth and plant resistance.

Technical readiness is the challenge for all of the bio-engineering methods discussed above. We generally begin integrating technologies into our models (first with high risking, later with lower risking) once they have surpassed TRL7. No bio-engineering method is there yet. Salk received a $35M grant in 2019, to accelerate its work, but prototype crop variants (corn, soybean, rice) are still not foreseen for five years. More pessimistically, scientists at RIPE have said it could take 15-years to deploy enhanced crops in the field. So while we will track this technology, it is not yet moving our models.

The Amazon tipping point theory?

The Amazon tipping point theory

The Amazon tipping point theory postulates that another 2-10% deforestation could make the world’s largest tropical rainforest too dry to sustain itself. Thus the Amazon would turn into a savanna, releasing 80GT of carbon into the atmosphere, single-handedly inflating atmospheric CO2 by 40ppm (to well above the 450ppm limit for 2C warming). This matters as Amazon deforestation rates have already doubled under Jair Bolsonaro’s presidency. This note explores implications, including international tensions, divestments, prioritization in a Biden presidency, and consequences for other transition technologies.


Global deforestation remains the single largest contributor to CO2e-emissions induced by man’s activities, more than the emissions from all passenger cars; and destruction of nature remains the largest overall contributor, more than all of China (chart below). This note is about a particularly worrying feedback loop in the Amazon rainforest, which could single-handedly wipe out the world’s remaining CO2 budget, effectively negating the impact of all other climate policies globally.

What is the Amazon tipping point theory?

The Amazon rainforest currently covers 5.5M square kilometers, comprising the largest, contiguous tropical forest in the world. 50% is in Brazil, and the remainder is spread around Peru, Colombia and half-a-dozen other South American countries. It contains 20% of all the planet’s plant and animal species, including 40,000 plant species alone.

Deforestation of the Amazon has reached 15-17% of its original area overall, and around 19% in Brazil. 800,000 square kilometers has been lost to-date (a land area equivalent to 2x California; or all of France plus Germany). Brazil’s annual deforestation rates have averaged 20,000 square kilometers per year from 1990-2004 (the land area of New Jersey or Slovenia). But the rate slowed to a trough of 5,000 square kilometers in 2014 due to improving environmental policies.

Unfortunately, more recently, Brazil’s deforestation rate has re-doubled (chart below). Jair Bolsonaro’s Presidency began in January-2019, following campaign pledges to ease environmental and land use regulations (which require 80% of legal Amazon land holdings to remain uncleared). Violations of these regulations are now said to be going unpunished. Bans on planting sugarcane in the Amazon have been lifted. Bolsonaro has even repudiated data published by Brazil’s own government agencies showing deforestation rates rising and accused actor and environmentalist, Leonardo DiCaprio of starting wildfires!

This matters because of the hydrology of the Amazon. Water in the basin tends to move from East to West. Each molecule typically falls as rainfall six times. It is repeatedly taken up by trees, transpired back into the atmosphere, and precipitated back down to Earth. Over half of the rain falling in the Amazon has originated from trees in the Amazon. It is a self-sustaining feedback loop.

The Amazon Tipping Point theory predicts that below some critical level of forest cover, this self-sustaining feedback loop will break. Less rainforest means less transpiration. Less transpiration means less rainfall. Less rainfall means less rainforest. Specifically, converting each hectare of forest to cropland reduces regional precipitation by 0.5M liters/year.

After the tipping point it is feared that the basin will transition into a savanna or scrubland. 50-100% of the forest cover would die back.

Unfortunately, this is not a ‘fringe’ theory. Many different technical papers acknowledge and model the risk, although specific climate models are imprecise, and do not always agree on timings and magnitudes. For example, the Western Amazon, closer to the Andes, might retain more forests than the East and Central parts of the basin. Another uncertainty is the moderating impacts of fire, as dryer forests will be more flammable, and thus more susceptible to slash-and-burn clearances, while raging fires will also reach further.

When is the tipping point? Various technical papers have estimated that the Amazon tipping point occurs when 20-25% of the forest has been cleared. This is an additional 2-10% from today’s levels, equivalent to deforesting another 100-600k acres, which could happen within 2-30 years.

What carbon stock is at risk of being released?

A typical forest contains around 300T of carbon per hectare (chart below). Thus 5.5M square kilometers of the Amazon is expected to contain 165GT of carbon. About 40% of the carbon is usually stored in trees (estimated at 60-80GT in the Amazon) and 60% is stored in roots and soils, which degrades more slowly. Hence, if just half of the remaining Amazon disappears, this would slowly release c80GT of carbon into the atmosphere.

Each billion tons (GT) of carbon released into the atmosphere is equivalent to raising atmospheric CO2 by around 0.5ppm. Hence a 80GT carbon release from the Amazon would by itself raise atmospheric CO2 from 415ppm today to around 455ppm. This single change (notwithstanding the continued and unmitigated burning of fossil fuels) would tip the world above the 450ppm threshold needed to keep global warming to an estimated 2-degrees (climate model below).

Can the tipping point be averted?

The solution to Amazon tipping points is technically simple: stop burning down forests and start re-planting them. This does not require electrolysing water molecules into hydrogen, smoothing volatility in renewable-heavy grids, or developing next-generation batteries. It requires something much harder: international diplomacy.

Inflammatory statements? In September-2019, Bolsonaro defended his environmental policies in a speech at the UN General Assembly. International critics were accused of assaulting Brazil’s sovereignty. Brazil considers itself free to prioritize economic development over environment.

Forest for ransom? In the past, Western countries have actually paid Brazil to safeguard its rainforests, although this arrangement has now fallen apart. Specifically, the ‘Amazon Fund’ was created in 2008. It is managed by Brazil’s state-owned development bank, BNDES. $1.3bn has been donated to the fund, from Norway (94%), Germany (5%) and Petrobras (1%). But after taking office, Bolsonaro has packed the fund’s steering committee with members of his inner circle, and in May-2019, he started using the Fund to compensate land developers whose lands were confiscated for environmental violations. Hence Norway and Germany suspended fund payments.

Divestment and trade tensions? As Brazil’s stance on the Amazon has grown more confrontational, it is possible that decision-makers may distance themselves from the country. Global investment funds have threatened to divest. (Could Brazil even surpass the coal industry as the divestment movement’s whipping boy?). Multi-national corporations may also be more cautious around investing in the country (but probably at the margin). Finally, Amazon deforestation is said to endanger future trade deals.

The Biden Factor? President-elect Biden may also seek to influence the Amazon issue. Biden stated the world should collectively offer Brazil $20bn to stop Amazon deforestation and threaten economic consequences for refusing. An executive order re-entering the Paris Climate Agreement would also help the situation (Brazil had actually committed to restoring 12M hectares of native vegetation under the accord). It will be interesting to see how Biden balances climate-focused priorities in the US with this arguably more urgent issue abroad.

Crucial Conclusions? If the Amazon surpasses its tipping point, there would be no chance of limiting atmospheric CO2 to 450ppm or preventing a catastrophic loss of biodiversity. Diplomacy is difficult. But fortunately, decision-makers can take measures into their own hands. Our note below profiles tree-planting charities. This is the lowest-cost decarbonization option we have found in all of our research. It restores nature, including the Amazon. Ultimately, we have argued that restoring nature may the most practical route to achieving climate objectives, while ‘bursting the bubble’ of other transition technologies.

Paulownia tomentosa: the miracle tree?

Empress Tree CO2 uptake

The ‘Empress Tree’ has been highlighted as a miracle solution to climate change, with potential to absorb 10x more CO2 than other tree species; while its strong, light-weight timber is prized as the “aluminium of woods”. This note investigates Empress Tree CO2 uptake. There is clear room to optimise nature based solutions. But there may be risks for the Empress.


Nature based solutions to climate change represent the largest and lowest cost opportunity in the energy transition. Those who follow our research will know we see potential to offset 15-30bn tons of CO2 emissions per year via this route (summary below).

The costs are incredibly low, at $3-10/ton, when reforestation efforts are well structured through reputable tree-planting charities (note below). Hence we argue that restoring nature will push higher-cost energy technologies off the cost curve.

Broadly, our reforestation numbers assume 3bn acres could be re-planted, absorbing 5T of CO2 per acre per year, which is the average across dozens of technical papers for typical deciduous forests in the Northern hemisphere (data-file below).

There are further optimisation opportunities to capture around 10T of CO2 per acre per year using faster-growing tree species, such as poplar, eucalyptus and mangrove. However, some commentators claim that another tree genus, known as Paulownia, can achieve an incredible 103T of CO2 offsets per acre per year.

If 100T/acre/year were possible, it would be a game-changer for the potential of reforestation. It would, in principle, only require 0.2 acres of Paulownia to offset the 20Tpa CO2 emissions of the average American. For comparison, population density in the Lower 48 is around 6 acres per American.

Paulownia: the miracle tree?

What is Paulownia? Paulownia is a tree genus, named after Princess Anna Pavlovna, daughter of Tsar Paul I of Russia (1754-1801). It has at least 6 species, of which Paulownia tomentosa is the fastest-growing “miracle” variety. This species also goes by the names: Empress Tree, Princess Tree and Kiri (Japanese).

Paulownia tomentosa can grow by a remarkable 6 meters in one year and reach 27m in height. It then adds 3-4cm of diameter to its trunk each year. It is shown below towering over the other plants in a garden (here, at about 1.5 years old).

Reasons for remarkable growth rates include that Paulownia is a C4 plant. This photosynthetic pathway produces more leaf sugar, especially in warm conditions. By contrast, most other trees are C3 plants and fix CO2 using the Rubisco enzyme, which is not saturated (creating inefficiency) and not specific (so it also wastes energy fixing oxygen). Paulownia’s leaves are also very large, helping it to absorb more light. It also simply appears to have a faster metabolism than other species. And finally, its wood is 30-40% less dense than other species, allowing it to accumulate a large size quickly.

Other Advantages?

Paulownia’s timber is highly prized and sometimes termed the “aluminium of woods”. It is light, at 300kg/m3 (oak is 540kg/m3) and 30% stronger than pine. It does not warp, crack or twist. It is naturally water and fire resistant. When used in flooring, it is also less slippery and softer than other woods (which is noted as advantageous for those prone to falling over). The wood is also suited to making furniture and musical instruments.

Pollutants are well absorbed by Paulownia’s large leaves, which can be 40-60cm long. Hence one study that crossed are screens examined planting Paulownia in a Northern Italian city, to reduce particulate concentrations toward recommended limits.

Other advantages are ornamental qualities with shade, “wonderful purple scented flowers” (below), which support honey bees, and the ability to restore degraded soils.

A final remarkable feature of Paulownia is that you can cut it down and it will re-grow, up to seven times, rapidly springing back from its stump.

Source: Wikimedia Commons

Costs of CO2 offsets using Paulownia?

Our usual model for reforestation economics is shown below, assuming a typical planting cost of $360/acre. Paulownia may be modestly more expensive to grow. Our reading suggests a broad range of $2-7/tree multiplied by c250 trees per acre in commercial plantations. The largest costs are cuttings and cultivation of saplings. Thereafter, paulownia requires “minimal management and little investment”. Hence if growth rates are 10x faster than traditional trees, all else equal, we would expect CO2 offset costs to be c10x lower, at $2-5/ton (including land acquisition costs at developed world prices).

Examples of Paulownia?

Over 2M hectares of Empress trees are cultivated in China, often being inter-cropped with wheat. But Paulownia cultivation in the Western world is more niche. As some examples: Jimmy Carter famously grows 15 acres of Paulownia trees on his farm in Georgia. As a commercial investment, WorldTree is an Arizona-based company that manages 2,600 acres of Empress Trees and plans to plant 30,000 acres more. It claims to be the largest grower of non-invasive Paulownia in the world. Furthermore, ECO2 is a privately owned Australian company, headquartered in Queensland. It claims to have cultivated a variety of Paulownia tree, which can reach 20m after 3-5 years and sequester 5-10x more CO2 than other trees, or around 2.5T of CO2 per tree. Finally, oil companies are exploring reforestation initiatives. For example, YPF noted in its 2018 sustainability report plans to test-plant 40 species of Empress Trees in 2019.

Problems with Paulownia?

Invasiveness? One of the largest pushbacks on reforestation is that large-scale planting of single forest varieties may impair biodiversity (a chart of all the pushbacks is below, with some irony that environmentalists call for drastic action to avert the perils of climate change, then often say, no, “not that drastic action”). In the US, Paulownia is categorized as an invasive plant. A single plant can produce 20M seeds in a year. In some States, such as Connecticut, sales of the plant are even banned. Paulownia did in fact exist in North America prior the last Ice Age. It was re-introduced from China in 1834, when seeds were accidentally released from dinnerware packaging materials. Whatever intuitions one might have, some factions are going to protest against Western cultivation of Paulownia.

But the greatest question mark over Paulownia’s CO2 offset credentials is in the numbers. Different studies are tabulated below.

Empress Tree CO2 uptake

103T of Empress Tree CO2 uptake per acre is the most widely cited number online. But this figure derives from a single study, conducted in 2005. Whose methodology is woefully rough. The study simply assumes a 12’x12′ planting of Paulownia (750/ha, 99.5% survival) and then uses a formula to estimate the CO2 uptake from the trees’ target height and width.

A follow-up study was published in 2019, estimating 38-90T of Empress Tree CO2 uptake per acre per year. But upon review, the upper bound is extrapolating the “maximum growth rate”, which is known to be 2-3x faster than the average growth rate (charts below). The study is also vague on its modelling assumptions. It was funded by a company that commercializes Paulownia plantations. Finally, the study itself notes “additional research is needed in order to quantify the carbon sequestration rates of Paulownia trees under the specific management regime employed by World Tree’s Eco-Tree Program, by continuing to collect DBH values over the 10 to 12 year harvest cycle.”

Empress Tree CO2 uptake

Achieving monster growth rates will vary with growing conditions. Ideal conditions are warmer climates (the tolerable range is -24 to 45C), flattish, well-drained soil with pH 5-9, <25% clay, <1% salinity, <2,000m altitude, >800mm rainfall and <28kmph wind. But past studies planting the Empress Tree in Eurasia have ranged from 3-15 tons of CO2 per acre per year, which is not so remarkable versus other tree varieties.

Diseases. Finally, dense clusters of trees may fall short of growth targets due to disease. Paulownia, in particular, is susceptible to an affliction known as ‘Witches Broom’, which causes the tips of infected branches to die, leading to a cluster of dead branches. The wood is of poor quality and the growth rate of the plant diminished.

We conclude that there is great potential for nature based solutions, especially for their optimisation to boost CO2 uptake rates. Paulownia may be among the options. However, more data may be needed in the West before it can be heralded as a miracle plant.

Our key points on Empress Tree CO2 uptake are highlighted in the research note sent out to our distribution list.

Copyright: Thunder Said Energy, 2022.