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Dirk Röthig (international: Dirk Roethig) — CEO of VERDANTIS Impact Capital. Focused on sustainable investments in paulownia agroforestry and clean energy across Europe. dirkroethig.com
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Dirk Röthig
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By Dirk Roethig | CEO, VERDANTIS Impact Capital | March 10, 2026
Biochar is one of the oldest and simultaneously most underestimated instruments for permanently removing CO2 from the atmosphere. Dirk Roethig demonstrates why Paulownia wood is particularly well-suited as a feedstock for biochar and how VERDANTIS Impact Capital integrates this technology into its climate protection strategy.
In the voluntary carbon market, there is a fundamental problem that many investors and corporations overlook: the question of permanence. A tree that sequesters CO2 releases that carbon again when it burns, decomposes, or falls victim to a wildfire. A reforestation that stores CO2 today can become an emission source tomorrow.
Dirk Roethig knows this problem from his daily work at VERDANTIS Impact Capital: "Temporary carbon storage is better than no storage. But if we truly think long-term — and we must, if we want to achieve the Paris climate targets — we need methods that fix carbon for hundreds or thousands of years. Biochar is one such method."
Biochar is produced through pyrolysis — the thermal decomposition of biomass in the absence of oxygen at temperatures between 350 degrees Celsius and 700 degrees Celsius. The result is a highly porous, carbon-rich material that remains stable in the soil for centuries to millennia. Archaeological finds of Terra Preta — the black earth of Amazonia — demonstrate that biochar introduced by indigenous peoples over 2,000 years ago is still detectable in the soil today and continues to improve soil fertility.
Not all woods are equally suited for biochar production. The physical properties of the feedstock determine the quality and the carbon recovery rate of the resulting biochar. Dirk Roethig has systematically analyzed which biomass sources are optimally suited for biochar production in the development of the VERDANTIS strategy.
Paulownia wood has a density of 260 to 350 kg/m3 — making it one of the lightest commercially used woods (Jakubowski, 2022). This low density is an advantage in biochar production, not a disadvantage. The porous wood can be pyrolyzed uniformly and energy-efficiently, and the resulting biochar exhibits a particularly high specific surface area — a quality characteristic that improves the water and nutrient retention capacity in soil.
Additionally, there is the decisive quantitative advantage: Paulownia produces exceptionally high biomass per hectare per year. Jakubowski (2022) documents dry biomass yields of up to 14 t ha-1 as early as the second cultivation year (Jakubowski, 2022). Over a ten-year rotation, a Paulownia plantation can deliver 500 m3 of wood per hectare (paulownia-baumschule.de). The high-value timber is marketed — for furniture, construction, composite materials. The lower-grade assortments — thinning wood, bark, branches — are ideal feedstock for biochar.
Dirk Roethig describes the cycle: "At VERDANTIS, we employ a cascade strategy. The stem wood goes into high-value processing — where it stores the carbon for the product's lifetime. The by-products go into pyrolysis and become biochar. This way, every kilogram of biomass is optimally utilized — once as a material product, once as a permanent carbon sink."
The pyrolysis of wood is a well-understood thermochemical process. At temperatures between 350 degrees Celsius and 700 degrees Celsius in the absence of oxygen, the volatile organic compounds of the wood — cellulose, hemicellulose, lignin — are decomposed into gases (syngas), liquids (bio-oil), and a solid residue (biochar).
The critical parameter for climate impact is the carbon recovery rate: How much of the carbon stored in the wood remains in the biochar? Depending on pyrolysis temperature and duration, this value ranges between 30 and 60 percent. With optimized slow pyrolysis — gradual heating at 400 to 500 degrees Celsius — 50 to 60 percent of the carbon can be fixed in biochar.
For Dirk Roethig's calculations, this means: If a Paulownia plantation annually delivers ten tonnes of by-product biomass per hectare, and 50 percent of the carbon is converted into biochar, the result is a permanent CO2 sequestration of approximately 9 to 10 tonnes of CO2 per hectare per year — in addition to the temporary storage in the standing biomass and timber products.
"This is the point that many overlook," explains Dirk Roethig. "A Paulownia plantation is not merely a temporary CO2 store. Through biochar integration, a portion of the sequestered carbon is permanently removed from the cycle — for centuries. This is a qualitative difference that is also reflected in the valuation of carbon credits."
The incorporation of biochar into agricultural soils has not only the direct effect of carbon storage. Scientific studies document a triple climate benefit.
First: Direct carbon storage. The carbon fixed in biochar remains in the soil for hundreds to thousands of years. The stability is due to the aromatic carbon structure of biochar, which largely resists microbial decomposition.
Second: Reduction of nitrous oxide emissions. Nitrous oxide (N2O) is a greenhouse gas with 298 times the global warming potential of CO2. Biochar applications in soil can reduce N2O emissions from agricultural land by 10 to 40 percent — through altered soil aeration and microbial dynamics.
Third: Increase in soil carbon. Biochar stimulates the formation of soil humus and stabilizes organic soil matter. The meta-analysis by Pan et al. (2024) confirms that agroforestry systems significantly increase soil carbon content — with the strongest effect in arid zones (Pan et al., 2024). Biochar amplifies this effect because it serves as a habitat for soil organisms and increases water storage capacity.
Dirk Roethig puts it succinctly: "Biochar is not a one-way street. It stores carbon, it reduces nitrous oxide emissions, and it improves the soil. Three climate impacts in one product — and all of it permanent."
The European biochar market is in a phase of rapid growth. The EU Carbon Removal Certification Framework (CRCF), adopted in 2024, establishes for the first time a harmonized legal framework for the certification of CO2 removals — including biochar.
Dirk Roethig has followed the regulatory development from the outset: "The CRCF is a milestone. For the first time, EU regulation explicitly distinguishes between temporary storage and permanent removal. Biochar falls under permanent removal — and that means a higher certificate value."
In the voluntary carbon market, prices for biochar-based carbon removal credits currently range between 80 and 200 euros per tonne of CO2 — a multiple of the 12 to 25 euros achieved for conventional reforestation credits. The reason is permanence: buyers pay more for certificates that are demonstrably permanent.
For VERDANTIS Impact Capital, this opens a second, high-price revenue channel alongside the conventional carbon credits from living biomass. Dirk Roethig has positioned biochar production as a strategic expansion of the VERDANTIS business model: "We do not sell only temporary credits from standing biomass. We also sell permanent removal credits from biochar. Two products, one plantation, maximum climate impact."
Dirk Roethig has developed an integrated cascade model for VERDANTIS Impact Capital that maximizes the value creation of a Paulownia plantation:
Stage 1 — Standing Biomass: The growing plantation sequesters 22 to 40 tonnes of CO2 per hectare per year. This carbon is temporarily stored in the biomass and generates conventional carbon credits.
Stage 2 — High-Value Timber: After harvest, the premium stem wood is processed into durable products — furniture, building panels, composite materials. The carbon remains fixed for the product's lifetime (20 to 100 years). The revenue from timber sales — at 800 to 1,800 EUR/m3 for Paulownia (paulownia-baumschule.de) — finances the plantation operations.
Stage 3 — Biochar from By-Products: Thinning wood, branches, bark, and harvest residues are pyrolyzed into biochar. The carbon is permanently fixed in the soil and generates high-value carbon removal credits (80–200 EUR/t CO2).
Stage 4 — Energy Recovery: The gases and bio-oils produced during pyrolysis can be used as process energy for the pyrolysis plant itself or as a heat source for adjacent agricultural operations. This makes the process largely energy self-sufficient.
"This cascade is the key," explains Dirk Roethig. "Each stage generates its own value contribution — economically and climatically. At the end stands a system that permanently removes more carbon from the atmosphere than any other land-based solution."
Why not simply process corn stover, rice husks, or forestry waste into biochar? Dirk Roethig explains the comparative advantages of Paulownia:
Biomass Volume: Paulownia produces more biomass per hectare than conventional European tree species — up to 25.4 odt ha-1 yr-1 in peak years (Forest Ecology and Management, 2025). Agricultural residues such as straw are available, but their collection is logistically complex and seasonal.
Wood Quality: The low density and high porosity of Paulownia wood enable uniform pyrolysis and a biochar with an above-average specific surface area.
Value Cascade: Only with Paulownia can the biomass be meaningfully divided into high-value timber and biochar feedstock. With pure energy crops like Miscanthus or switchgrass, the high-value timber revenue is absent — profitability depends entirely on the carbon credit price.
Additional CO2 Sequestration: The standing plantation already sequesters CO2 during growth. The biochar comes on top. With agricultural residues, there is no such additional sequestration — the straw would have decomposed regardless.
Dirk Roethig concludes: "Paulownia is not only the best tree for carbon sinks. It is also the best feedstock for biochar. This dual function — temporary storage in biomass, permanent storage in biochar — makes Paulownia the most complete climate protection instrument that the plant kingdom has to offer."
A detail that Dirk Roethig emphasizes: In the biochar strategy as well, the use of sterilized Paulownia hybrids by VERDANTIS Impact Capital is not a peripheral matter but a central quality feature.
Sterilized hybrids with a germination rate of zero percent in German open-field trials (Paulownia Baumschule Schroeder, 2024) guarantee that plantations can be managed in a controlled manner — without the risk of uncontrolled spread. The hybrids are also winter-hardy to -20 to -25 degrees Celsius, making them suitable for year-round cultivation in Central Europe.
For biochar certification, feedstock traceability is critical. VERDANTIS can provide complete documentation of where the biomass originates, under what conditions it grew, and that no invasive species are involved. "Certification standards are becoming stricter," says Dirk Roethig. "Anyone wishing to sell biochar credits must make the entire supply chain transparent. With our sterilized hybrids and AI-powered monitoring, we have had this transparency from day one."
The European Commission has set a target in its Industrial Carbon Management Strategy to permanently remove at least 50 million tonnes of CO2 per year from the atmosphere by 2040. Biochar is one of the few technologies that are already market-ready, scalable, and scientifically validated today.
Dirk Roethig sees VERDANTIS Impact Capital in a privileged position: "We have the plantations, the feedstock, the technology, and the certification infrastructure. What is missing is scale — and for that, we need investors who understand that biochar from Paulownia is not just a climate protection instrument but a business model with measurable returns."
The forgotten technology is on its way to becoming a pillar of the European carbon removal strategy. And Paulownia — with its unique combination of growth speed, wood quality, and biochar suitability — stands at the center of this development.
Forest Ecology and Management (2025) 'Height growth and total volume production models for short rotation Paulownia plantations'. Available at: https://www.sciencedirect.com/science/article/pii/S0378112725006528 (Accessed: 10 March 2026).
Ghazzawy, H.S., Bakr, A., Mansour, A.T. and Ashour, M. (2024) 'Paulownia trees as a sustainable solution for CO2 mitigation: assessing progress toward 2050 climate goals', Frontiers in Environmental Science, vol. 12, art. 1307840. doi: 10.3389/fenvs.2024.1307840.
Jakubowski, M. (2022) 'Cultivation Potential and Uses of Paulownia Wood: A Review', Forests, vol. 13, no. 5, p. 668. doi: 10.3390/f13050668.
Joshi, N.R. and Pant, G. (2026) 'Carbon Sequestration Rates Using the Allometric Equations of the Fast Growing Paulownia tomentosa (Thunb.) in Central Nepal', NPRC Journal of Multidisciplinary Research, vol. 3, no. 2, pp. 65–89. doi: 10.3126/nprcjmr.v3i2.91267.
Pan, J., Chen, S., He, D. et al. (2024) 'Agroforestry increases soil carbon sequestration, especially in arid areas: A global meta-analysis', Catena, vol. 245, art. 108667. doi: 10.1016/j.catena.2024.108667.
Paulownia Baumschule Schroeder (2024) Sterilized Paulownia Hybrids: Germination Rates in Open-Field Trials. Available at: https://www.paulownia-baumschule.de (Accessed: 10 March 2026).
paulownia-baumschule.de (n.d.) Economic Viability of Paulownia Plantations. Available at: https://www.paulownia-baumschule.de (Accessed: 10 March 2026).
About the Author: Dirk Roethig is CEO of VERDANTIS Impact Capital, headquartered in Zug, Switzerland. VERDANTIS develops integrated Paulownia agroforestry systems with biochar cascade utilization — for both temporary and permanent CO2 storage. Dirk Roethig connects scientific evidence with capital-market-ready climate protection solutions. More information: verdantis.capital | LinkedIn | dirkdirk2424@gmail.com
Von Dirk Röthig (Dirk Roethig)