Afforestation, reforestation and the wider “land sink” bucket

Afforestation — planting trees where there were none in recent history — and its close cousin reforestation (replanting where forest was recently cleared) remain the largest single category of carbon removal sold today, by both tonnes issued and dollars transacted. The pitch is straightforward: trees pull CO₂ out of the air through photosynthesis and lock a fraction of it into wood, roots and soil organic matter for as long as the forest stands. The complications are equally straightforward: forests burn, get cut, get sick, and the carbon goes back. For a senior buyer comparing pathways, the central question is not whether trees sequester carbon — they obviously do — but how durable, additional and well-measured a given project actually is, and how that compares to engineered alternatives at 10–100× the price per tonne.

In practice, the directory groups several related land-sector activities under this heading: tree planting (afforestation/reforestation, or ARR), improved forest management (IFM), agroforestry, grassland and soil carbon, and mangrove restoration. They share a biological mechanism and most of the same durability headaches, so it is reasonable to discuss them together — provided one keeps track of which activity a given supplier actually does.

How it works

The underlying science is well-trodden. Net carbon uptake on a project site is the difference between gross primary productivity and total ecosystem respiration, integrated over the project lifetime and netted against a counterfactual baseline. A young, fast-growing temperate plantation can sequester 5–15 tCO₂/ha/yr above-ground; tropical reforestation on degraded land can be higher early on; mature forests approach steady state. Roughly 20–40% of the carbon ends up below ground in roots and soil, where turnover times are longer than in leaves and branches.

Three pieces of recent literature are useful framing. Rogelj et al.’s widely cited treatment of what “net zero” actually requires makes clear that land-sector removals are doing heavy lifting in every IPCC-consistent pathway, but only if the carbon stays put on multi-century timescales — which is not what most ARR projects actually guarantee. Terlouw et al.’s life cycle review of CDR technologies shows that nature-based options have the lowest cost and energy footprint per tonne but the widest uncertainty bars on net removal. And the biochar-in-agriculture meta-review is a reminder that soil-carbon claims, in particular, have been revised downward repeatedly as field data has accumulated.

Who’s doing it

The directory’s afforestation cohort spans every flavour of the activity:

  • Rainforest Builder runs large-scale native-species tropical replanting across Sierra Leone, Ghana and Guinea, with a workforce above 2,500.
  • Chestnut Carbon, backed by Kimmeridge, does U.S. afforestation on private land and sells Gold Standard credits; it is one of the larger pure-play developers in North America.
  • Aurora Sustainable Lands takes a different approach: it buys roughly 1.65 million acres of previously industrial U.S. forestland and lengthens rotations under an Improved Forest Management protocol.
  • Terraformation supports third-party reforestation projects through seed banking and its open-source Terraware management software rather than owning the land itself.
  • MORFO plants with drones and pre-germinated seed capsules in the Atlantic Forest, Amazon and Gabon — a feedstock-side bet on planting cost.
  • Funga and Loam are both microbial plays: Funga inoculates pine seedlings with native mycorrhizal communities to accelerate growth; Loam treats crop seeds with fungal endophytes to push more carbon into mineral-associated soil pools.
  • Grow Indigo and Klim sit in the agricultural soil-carbon corner, working with smallholders in India and farmers across Europe respectively under Verra VM0042 and DIN ISO 14064-2.
  • Pina Earth and Ocell develop IFM projects in DACH-region forests using forest-simulation software for baselining and MRV.

Earlier-stage outfits like Arbreen, which says it is targeting 5–10 MtCO₂/yr per country across 5–20 African countries, illustrate the gap between announced ambition and operating project portfolios in this segment.

The durability question

This is where afforestation gets hard. Engineered CDR pathways quote storage durations in the thousands of years; forests carry storage assumptions of 40 to 100 years in most registry methodologies (Verra VM0047, CAR’s Mexico Forest Protocol, the Label Bas-Carbone). Permanence is managed through buffer pools — typically 10–20% of credits withheld against reversal — but recent fire seasons in California, British Columbia, Australia and Siberia have raised legitimate questions about whether buffer pools are sized correctly for a warming climate. CarbonPlan’s published reviews of the California compliance buffer concluded it was already drawn down faster than projected within a decade.

MRV (measurement, reporting and verification) is improving fast: LiDAR, satellite biomass products, and tools like TREEO’s single-tree app and Cultivo’s geospatial platform have made remote monitoring tractable. But baselines remain the soft spot. Almost every credibility scandal in the voluntary market over the last three years has come back to counterfactuals — what would the land have done without the project. Soil-carbon projects from suppliers like Boomitra, Ruuts and Grassroots Carbon face an additional sampling-density problem: SOC stocks are spatially heterogeneous and slow-changing, and the cost of measuring them properly competes with the price of the credit.

Open questions for the next twelve months

A reader returning in a year should look for: (1) whether buffer pools across the major registries are recalibrated upward after another fire season; (2) whether the new ICVCM Core Carbon Principles assessments approve or reject the dominant ARR and IFM methodologies; (3) whether any of the microbial-amendment players (Funga, Loam) publish independently replicated field data on additional sequestration above untreated controls; (4) whether prices for high-quality ARR credits — currently $20–50/tonne — converge toward or diverge from engineered removal at $100–500/tonne; and (5) whether large-claim developers like Arbreen translate megatonne pipelines into issued, retired credits.