It was an early start as I was lucky enough to get a place on "The Davos Express", and it was a flashback to my yearly school trips on the Hogwarts Express - treating the journey as a chance to meet and catch up with contacts on the way from Zurich.

For many years there have been demonstrations against WEF, but now, since the start of the Climate Hub Davos run by Green Up Switzerland, nature, biodiversity, climate and community are part of the conversation. This is the place to be, with people from diverse backgrounds sharing their experiences and solutions for a greener future.

I joined Clarmondial's session 'How Localised Nature Data can Empower Business and Unlock Finance', which included some really interesting perspectives. We heard from scientists supporting sustainable cacao farmers in Indonesia, nature and climate risk specialists from reinsurance, and sustainable timber investment groups, amongst others. It was encouraging to see so many different perspectives all converging on protecting nature.

I was struck by a couple of comments. On assessing climate risks: "How you interpret data is crucial to interpreting risk." This resonated with me. There is so much talk about data, and so little consideration of experience interpreting it - something we constantly consider while building belian's products. On nature credits: "These already exist, and a market already exists - high quality carbon credits that can demonstrate their community and biodiversity benefits." There certainly seems to be consensus in many areas of the market.

Just as when skiing in Davos, restaurants tend to be a bit busy and pricey, so I got a packed lunch from Coop and found a bench in the sun as I often do at conferences. While eating a boiled egg and some fruit, I was lucky enough to be joined by various friendly people, including Cameron from Bottletop.

I learnt that #togetherband is made with Humanium - metal repurposed from decommissioned illegal firearms seized in Central America. The bands are handmade at an atelier in Nepal by women rescued from human trafficking. Their mission is to share the UN's 17 Sustainable Development Goals, and they do it in a beautiful way. As Cameron was tying this togetherband around my wrist he explained how the dismantling of guns is an important part of the process for the young men processing their trauma. Certainly a project I would like to support.

I had many conversations at the Climate Hub around the sustainable development goals, and I particularly appreciate learning about concepts that are not my core expertise. While belian may appear focused on life on land and climate action, all of the sustainable development goals align with our values. I wonder if the next togetherband might feature upcycled beads of belian, the Bornean ironwood tree we are named after?

I then took a little break from work to look at skis. I had some really good advice from Silvan at Angerer Sport. I would certainly recommend checking out their ski test centre on Jakobshorn. I certainly plan to.

After years of working on forest carbon baselines, it's good to see the carbon market conversation maturing, and after years of WEF, it's good to see that nature is properly on the table, despite what some make you believe.

With restoration and tree-planting projects back in the spotlight, partly driven by growing scrutiny of baselines in avoided-deforestation projects, we are revisiting a paper we published five years ago in Science: Active Restoration Accelerates the Carbon Recovery of Human-Modified Tropical Forests. The study combined two decades of permanent-plot measurements with high-resolution biomass maps, produced with airborne LiDAR, in Sabah, Malaysian Borneo. This allowed us to directly compare carbon recovery in areas that had been allowed to regenerate naturally with areas that had received active restoration, including enrichment planting of dipterocarps and routine cutting back of climbers and competing vegetation. Ultimately we found that in addition to the already impressive natural regeneration in this area, active restoration accelerated biomass accumulation substantially, around 50% faster than in the areas naturally regenerating. Follow-up research published in 2026 has since shown that climber (liana) cutting alone drives much of that gain — separating the contribution of seedling planting from climber cutting required a designed experiment with proper controls. As funding shifts towards restoration projects, often viewed as more 'additional' than avoided-deforestation, this work is relevant because it established a robust empirical counterfactual baseline on which to measure the efficacy of active restoration.

Why forest protection matters for forest carbon recovery

Natural regeneration performed well, but only because the forest had been protected from further disturbance. The surrounding forest, outside the study area, was logged repeatedly (Reynolds et al., 2011). Each round of logging took the most valuable stems first, and in Sabah that meant belian, the Bornean ironwood we are named after, which is why mature belian are now rare in logged forest. Without sustained protection, the recovery rates we measured would not have been possible, and neither the impressive gains from natural regeneration nor the additional gains from active restoration would persist; both depend on the balance between growth and degradation. Growth and degradation are not separate silos; they result from interacting anthropogenic and natural processes that coexist and must be measured simultaneously. Sustained protection on the timescales required by frameworks like Article 6.4's permanence rules is exactly the policy question covered in our piece on the ICVCM Permanence Trust and nature finance.

The counterfactual question: what would have happened?

The growing scrutiny of baselines in avoided-deforestation projects essentially questions the counterfactual, i.e. what would have occurred in the absence of the conservation intervention and, more specifically, how much deforestation and degradation would have occurred. However, the factor that is often missed is that a counterfactual is only an estimate as the true baseline is unknowable. This is inevitable because observing "what would have happened" would require leaving the area unprotected and observing the deforestation rate, which is obviously incompatible with implementing a conservation project. There are, however, a variety of methods that enable us to estimate this counterfactual and quantify the uncertainty empirically, although these methods are still in development and remain underutilised in forest carbon projects.

Restoration projects need counterfactual baselines too

Just as with avoided deforestation projects, restoration and tree-planting projects also require a counterfactual to estimate their impact. In the restoration case, the primary questions are: if you hadn't planted a tree, what would have been there in its place? Bare ground, or perhaps some natural regeneration? And, if forest recovery is the most likely alternative scenario for the site, what would the rate of recovery have been? In both restoration and avoided-deforestation projects, the underlying question is the same: how does the carbon balance change over time compared with what would have happened without the intervention? For tree planting that question is now formalised in Verra's methodology, and our page on VM0047 baselines and reference areas sets out how we answer it.

The real question is whether counterfactual baselines are robust

Although active restoration accelerated carbon recovery, the additional gains need to be considered alongside the restoration costs. Comparing the difference between natural regeneration and active restoration with global cost estimates makes it clear that, given the expense, restoration is more justified in the most degraded or disconnected areas where natural regeneration would be most inhibited. Recent global assessments also show that the majority of remaining forest carbon potential lies in existing forests, meaning that protection delivers much of the climate benefit, with restoration valuable where forests have been heavily degraded or removed (Mo et al., 2023). The baselines of avoided-deforestation projects have been criticised, but restoration projects also depend on a counterfactual baseline to demonstrate impact. The issue is not whether baselines exist, but whether they are robust. Impact evaluation of both restoration and avoided-deforestation ultimately relies on the same principle: clearly estimating the difference in carbon balance between the intervention and a robust counterfactual baseline. The earth observation side of how we build those baselines is the subject of our ML4EO 2026 work, and the method itself is described step by step on our technology pages.

Permanence has remained a core sticking point in Nature-Based Solutions since the first debates about including these activities in the Kyoto protocol. While Verra unlocked the first generation of AFOLU activities at scale, through the use of a Non-Permanence Risk Assessment and buffer pool approach, this hasn't been enough to bring NBS into compliance markets at scale.

Now that we've seen significant improvements in carbon accounting in these activities, will solving the permanence problem once and for all finally be the thing that unlocks Nature-Based Solutions at scale?

Under the Paris Agreement, permanence remains a sticky subject. New guidance needed for A/R PACM methodologies, namely the "Reversal risk assessment tool" and "Concept note: Options for the implementation of paragraph 62 of the 'Standard: Requirements for activities involving removals under the Article 6.4 mechanism" are in the Methodological Expert Panel's 2026 workplan, with an updated concept note expected by the end of this month.

Could a Permanence Trust unlock Nature-Based Solutions?

ICVCM also continues work on this subject through its ongoing work programmes, including exploring the concept of a "Permanence Trust" that could manage permanence monitoring and compensation, as needed, beyond the crediting period overseen by standards bodies.

Liana cutting accelerates the recovery of logged tropical forest three times faster than tree planting, at one tenth of the cost. That is the headline of our new paper in Current Biology, out of the Sabah Biodiversity Experiment in Borneo. The result matters not only for what it shows but for the experiment behind it: the Sabah Biodiversity Experiment is one of the few places where forest restoration interventions have been tested against proper controls. A new Verra methodology, now in public comment, is being built on exactly this kind of evidence.

VM0047 made a brave call. It locks the developer's matched reference areas at validation and keeps them fixed for the project's full crediting period. For most ARR projects under the VCS Standard, that crediting period runs for 20 to 40 years. Long-term commitments are good for forests, but they mean you have to make the right choice up front. The separate question of what happens after the crediting period, the post-crediting permanence debate around the ICVCM Permanence Trust and Article 6.4, is where the next set of NBS battles are being fought. Our Article 6 policy explainer tracks where those rules stand.

The choice was deliberate. A baseline that lets developers quietly upgrade their comparators when the numbers start looking too good is not a baseline at all. By fixing the matched controls at validation, VM0047 closes that loophole. It is one of the more credibility-protecting moves in modern carbon methodology design.

But that brave methodological call makes the developer's matching a defining moment. One choice at validation, which is locked for decades.

Why your VM0047 control plots define your project for the full crediting period

Reference areas drive the performance benchmark for every issuance over a project's life. Each verification computes the benchmark on the same locked control plots, using whatever new stocking-index data has accrued. The benchmark updates over time. The matched controls behind it do not.

VM0047 makes this explicit. Once the match passes Verra's quality test, "the final selection of control plots and their respective weights are then fixed... for the duration of the crediting period." The same control plots, with the same weights and coordinates, will define your project's benchmark for twenty, thirty, sometimes more than forty years.

This is not one of many small calls in project development. It is the single largest methodological choice a developer makes.

What makes a VM0047 baseline defensible?

Reference area selection is also the part of the methodology most exposed to challenge. Even when the developer does the work with care and integrity, with expert analysts and the best available data, the selection is open to questions and attack. Which covariates were used? What distance threshold was applied? Which polygons were excluded? Why one set of plots and not another?

This is not a hypothetical concern. Across the broader carbon credit literature, baseline construction is consistently identified as the lever where overstatement enters the system. Recent work in Nature Communications attributes systematic over-crediting in forest carbon programmes to selection-bias mechanisms in baseline determination (Swinfield et al. 2026). Reference area selection is the step under scrutiny in most of these accounts.

A global evaluation of voluntary REDD+ projects published in Conservation Biology (Guizar-Coutiño et al. 2022) found that a more defensible matching procedure can both confirm real reductions and substantially adjust their estimated scale. The methodology behind the match matters.

Buyers know this. A project that can show its reference areas were chosen by a third-party process, with documented covariates and reproducible outputs, has a stronger position with both buyers and ratings than one that picked its own.

The challenge for the developer, of course, is that even doing the selection well is not the same as being seen to have done it well. Conflict-of-interest logic is hard to refute when the developer holds the pen.

What does independent VM0047 reference area selection look like?

Independence alone is not enough. A consultant or service provider can be accused of the same kinds of bias as a developer the moment they are paid to produce a result. What matters is whether the selection is reproducible, auditable, and removes the role of judgement as much as possible.

There are two key elements to selecting reference areas: finding matching areas, and the criteria for how they match. VM0047's prescribed procedure for matching is based on the closest controls on the stocking index, which are then locked in and used for the benchmark. But how the candidate pool is built is even more important. Two areas can look identical on the stocking index while sitting in completely different landscapes. A back garden surrounded by houses can match a forest patch on greenness alone. Without that context, the match returns plausible but wrong comparators. This is the pixel-level problem we discussed at ML4EO 2026: per-pixel accuracy means little if it produces matches that do not make landscape sense.

Independent VM0047 reference area selection, done well, means a third party identifies the candidate areas before the prescribed matching runs. Best practice is to use a process that another analyst running the same procedure would replicate exactly. The developer does not choose the inputs. The methodology runs as written within the regions returned.

The selection should be reproducible: same inputs, same outputs, regardless of who runs the procedure. It should be auditable, with every covariate, threshold, and exclusion documented and inspectable. It should be vendor-agnostic, sitting upstream of any biomass or stocking-index provider so the developer is not locked into a downstream stack. And it should be compliant with the methodology: VM0047's prescribed matching procedure runs as written within the candidate areas the search returns.

This is the service belian provides, and our page on VM0047 baselines and reference areas sets out what we deliver, step by step. We sit upfront in the developer's pipeline and run VM0047's prescribed matching as written within the regions we identify. We do not modify or replace any of Verra's prescribed procedures. We add an upstream step the methodology leaves to the developer. We make sure the procedures are run in a way that is reproducible and auditable, and free from any conflict of interest.

That distinction matters. The developer ends up with reference areas they can defend to a VVB, to a buyer, and to a ratings agency, because they did not pick them.

Faster baselines, faster credits

Reference area selection is also one of the most time-intensive parts of VM0047 baseline preparation. In-house, building the donor pool, running the matching procedure, and validating the quality thresholds can stretch across weeks or months of analyst time per project.

Independent automated selection compresses that timeline. The output arrives in days, not weeks. For developers, that means shorter project preparation, smaller upfront cost, and an earlier first issuance. For programmes operating across many sites, it shifts a one-off bottleneck into something predictable and budgetable. ARR economics are notoriously thin. Anything that compresses the path to first issuance moves projects that would otherwise be marginal into financial viability.

Faster, defensible baselines also help on the validation side. The cleaner and more auditable the selection record, the less time the validating body spends on questions during validation review. The benefits compound.

VM0047 is the right methodology. Make sure it runs on the right ground.

VM0047's lock-in is one of its strengths. It is also the reason the developer's first decision is heavier than any decision they will make later. Choose well, and the methodology rewards the project for the full crediting period. Choose poorly, and the project lives with that decision for the same length of time, and may lose credibility.

If you are working on VM0047 projects and want to stay up to date with developments in independent reference area selection, sign up below.

Last year we supported ML4EO, the Machine Learning for Earth Observation conference in Exeter. Many different researchers and practitioners showing what's now possible with satellite data, foundation models, and geospatial AI across conservation monitoring, carbon markets, and environmental integrity. We're sponsoring again this year because we think this community matters.

What machine learning for earth observation gets wrong

The advances in geospatial AI are exciting, and this is why we are supporting the conference. Foundation models trained on petabytes of satellite imagery. Embeddings that capture landscape similarity without hand-crafted features. New ways to monitor forests, map habitats, and track land use change at global scale. It's what we work on every day.

But one of the talks that stuck with us most from ML4EO 2025 wasn't about a new model or a new dataset. It was about caution. Karen Anderson and Bri Pickstone from Exeter presented "Why ML != EO: From Black-Box to the Accuracy Paradox", arguing that the remote sensing community is adopting machine learning faster than it's thinking about what these tools actually represent. We agree.

Remote sensing scientists work with composites every day. Mosaics stitched from images captured at different times, from different viewpoints. Few people stop to question them. In an age of machine learning for earth observation, this is getting more pronounced. Models built on composites that have not been questioned. Pixels treated as more accurate than ground truth when the same tree can look completely different one day apart because of sun angle. Pixels are useful abstractions, but they are abstractions.

Why this matters for carbon and biodiversity conservation

This is where it connects to what we do. If you can't be certain what a pixel represents, what does that mean for carbon credit baselines? For conservation monitoring? For any claim that says "this forest is intact" or "deforestation happened here"?

Deforestation doesn't occur on a pixel. It occurs across landscapes, at different scales, driven by processes that don't respect grid boundaries. The question isn't "what class is this pixel?" It's "what would have happened here without intervention?" That's a fundamentally different question, and it needs different tools. At belian.earth we work with embeddings rather than pixel classifications. We compare trajectories across larger scales rather than labelling individual pixels. We do this not because it's fashionable, but because the pixel-level assumptions don't hold up when the stakes are real.

Consider the accuracy paradox. A land cover map with 92% overall accuracy sounds good. But at ML4EO, Bri showed that heathland was only detected 34.8% of the time, misclassified as grassland. High overall accuracy hiding a catastrophic failure for the habitat class that actually mattered. As Karen highlighted, "finer resolution data does not always equal better quality information." When decisions about carbon credits or conservation outcomes depend on these classifications, that gap matters.

Come find us at ML4EO 2026

We will be at ML4EO 2026.

This year's keynotes include Dr Emily Lines (Cambridge), who is developing new methods for monitoring forest structure and biodiversity using remote sensing from the ground to satellites, and Tomislav Hengl (OpenGeoHub) on open geospatial science, which we are big supporters of. It's a strong programme.

The workshops extend the conversation. Jakub Nowosad is running a session on where your models can be trusted, using spatial cross-validation to test whether predictions hold outside training areas. It's exactly the kind of rigour the field needs more of. IBM are back with hands-on sessions on TerraTorch and foundation model fine-tuning. And there are rumours of an introduction to TESSERA, the Cambridge geospatial foundation model, from the lead developer. For anyone working with earth observation embeddings, these are worth the trip alone.

If you're working in conservation monitoring, carbon markets, or environmental integrity and want to talk about what credible counterfactual baselines look like, come find us.

ML4EO 2026

Update, September 2026: the poster prizes, and 2027

The post above was written before the conference. ML4EO 2026 took place in Exeter in June, and our sponsorship went on the student poster prizes. Three winners, three very different topics, all sitting close to work we care about.

Alan Nare (University of Exeter and Shangani Holistic Ranch, Zimbabwe) attributed 36 years of woody encroachment in African savannas to fire, herbivory and climate drivers, using machine-learning-calibrated Landsat and process-based models. A really nice piece of work with Guy Lomax, Tapiwa Gumbo, Peter Makumbe and Andrew Cunliffe.

Deha Agus Umarhadi (Ludwig-Maximilian University of Munich and Remote Sensing Solutions) mapped aboveground biomass across peat swamp forests in Central Kalimantan, combining Planet NICFI imagery with airborne LiDAR. A very clear poster, with Florian Siegert.

Franziska Müller (University of Leipzig) tested whether spatial, spectral or temporal information matters most for deep learning classification of forest disturbance, with Gustau Camps-Valls and Ana Bastos.

Big thanks to the Centre for Environmental Intelligence team at the University of Exeter and everyone at ML4EO for a really strong conference. We have already agreed to sponsor ML4EO 2027, poster prizes included.

The carbon market has an integrity problem. Everyone knows that. But it is not the one anyone is talking about anymore. The problem is in the carbon baseline.

The major market upset was driven by West et al. (2023), who argued that many forest carbon projects overestimated deforestation rates in their baselines (see our response to their article). We contest the methods used, but the authors raise a pertinent point: existing methods do not do a good enough job of causally measuring the true impact of carbon projects.

Since then, the market has shifted. There is a greater desire for "high-integrity" credits. Good. But many appear to wilfully ignore the criticisms the market has faced, claiming we can restore trust through better measurement and improved predictive modelling. Better measurement is welcome, of course. But while the industry obsesses over which biomass map to trust, the real uncertainty, the real risk, is somewhere else entirely. It is in the carbon baseline.

Efforts continue to eke out greater performance from forest allometry and machine learning upscaling. Allometry also leans on wood density, which varies several-fold between species; belian, the Bornean ironwood we are named after, sits near the top of the range for Bornean trees. New global and regional canopy height models are released on a near-weekly basis, with growing potential for model ensembles and fine-tuning. Perhaps all of this is soon to be made redundant by ESA's P-Band SAR BIOMASS mission.

None of this is wasted effort. We have been building biomass maps for years and welcome every advance. But having built them ourselves across multiple carbon projects, we have come to realise something uncomfortable. The real uncertainty is not in precisely how many tonnes of carbon are in the forest. It is in what would have happened to the forest without the project. The spread between biomass maps is small. The spread between a good baseline and a bad one is enormous.

The carbon credit integrity crisis everyone is ignoring

Carbon credit integrity depends on many things. But the one question that determines whether a credit represents a real change in atmospheric CO₂ is simple: would it have happened anyway? Get that wrong and five different ratings agencies will each charge you to tell you the credit is worthless. It does not matter how precisely you measured the trees if your counterfactual scenario is more fiction than fact.

The industry knows this. It is exactly where past integrity failures came from. Carbon baselines that assumed the future would look like the past. Projects claiming credit for "saving" forests that were never under threat. That is why baseline has become a loaded term. People would rather focus on biomass maps, where you can at least get precision, than touch the baseline question, where you cannot hide behind a pretty map.

It is not just about the biomass maps

A road gets built. A policy changes. Commodity prices shift, or a new president takes office. The real trajectory of deforestation changes, and a historical baseline built from historical trends cannot keep up. It is looking backwards when it should be taking in the full picture. What is happening right now, to similar forests, that are not protected? That wider view is what matters.

Some have taken this further, arguing that because social-ecological systems are complex, causal attribution is fundamentally impossible and carbon markets should be abandoned altogether (Rana et al., 2026). We disagree. Complexity is not a reason to give up. It is exactly the kind of problem science exists to solve, and as we argued at ML4EO 2026, pixel-perfect classification means little if the landscape-level counterfactual is wrong.

The carbon market has spent years refining how we measure trees. It is time to be just as rigorous about what we compare these measurements against. Designed experiments like the Sabah Biodiversity Experiment show one path: build the controls in from the start.

belian.earth exists to solve the carbon baseline problem. Read about how counterfactual baselines work, see how we build avoided deforestation baselines, or see the technology that builds them.

belian.earth is named after the belian tree. In English it is the Bornean ironwood, Eusideroxylon zwageri, and it lives for more than a thousand years. With its high wood density it stores a large amount of carbon, and it is so resistant to rot and termites that the timber is highly sought after.

Nature-based carbon is criticised for not lasting. This tree does. For us, the name stands for permanent carbon storage and our long-term view.

It also links us to our roots. I spent years working in the forests of Sabah, learning from the people there, and belian is the tree everyone gets excited about. There was such heavy logging of belian trees across Borneo that they are not so common in logged forest. I have fond memories of the whole field team crowding round when we found a belian in the field plots. So we named the company after belian. We're here for the trees, after all.

What the word belian means

The Bahasa Melayu (Malaysian language) name for the belian tree is belian, and the word is used across Sabah, Sarawak and Brunei. Kayu belian refers to the timber, and the standing tree is pokok belian. Cross into Indonesian Borneo and the same species is ulin, or kayu ulin for the wood, which is the name most of the Indonesian research uses. In the timber trade both words point at this one species.

The tree itself carries a lot of names. In Indonesia: ulin, belian, tebelian, tulian and onglen. In Sabah you will also hear tambulian. The Berawan of Sarawak call it terras. In the Philippines it is tambulian or sakian. In English it is Bornean ironwood or Borneo ironwood, and in older timber records billian; the French trade calls it bois de fer. In Jambi in Sumatra people tell several ironwood varieties apart by eye, and a 2015 study set those local names beside the trees' form and their DNA (Irawan et al. 2015). Sarawak gazetted belian as its official state tree on 20 March 1984 (Sarawak Gazette No. 1484). In Iban, a language of Sarawak, belian is a diamond, the stone and the suit of cards. I used to think that was because a diamond is pure carbon and very hard, like belian wood. In actual fact, that is a loanword from the Dutch briljant.

The scientific name is Eusideroxylon zwageri. Eusideroxylon is built from the Greek for iron and wood, with "true" on the front. The species is named after Zwager, a Dutch official, and the tree was described by Teijsmann and Binnendijk in 1863 (Kew, Plants of the World Online).

Two other Malay words are spelled belian and have nothing to do with the tree. One is beli with the ending -an, meaning a purchase, which is useful when you're shopping for field supplies. The other is an old word for a shaman, still sometimes used in Borneo, which goes back to an Austronesian root reconstructed as *balian, "shaman, shamaness, shamanistic ceremony" (Blust and Trussel, Austronesian Comparative Dictionary). Same spelling, different words: none of the three is related to the others.

That third sense is not dead in Borneo. Among Dayak communities in East Kalimantan, the Benuaq and the Luangan among them, a belian is a healing ceremony: an overnight performance led by a shaman to call back the spirit of someone who is ill. Herwig Zahorka catalogued the plants used across a four-night belian sentiu ritual (Zahorka 2007), and Isabell Herrmans has written a book on the practice (Herrmans 2015). So in Borneo the word belian can point at a tree or at a ceremony, depending on who you ask and where you are standing. The same root surfaces right across the region: a healer is a balian in Bali, a babaylan in the Philippines and a bobohizan among the Kadazan-Dusun of Sabah (Blust and Trussel, Austronesian Comparative Dictionary).

What belian is: a thousand-year tree in the Lauraceae family

If you look at the forest canopy in Borneo, it is dominated by dipterocarps, with dipterocarps accounting for up to 80% of the canopy in many of these forests (Whitmore 1984). The family is a very diverse one, so while the canopy is many different species, it mostly comes from a single family.

The belian sits apart from all that. It is in the Lauraceae family, the laurels, with bay, cinnamon and avocado for relatives, and it is the only species in its genus. It grows to about 50 metres, with a trunk that can pass a metre across (IUCN 2025). I first saw it at Sepilok Forest Reserve, near Sandakan, twenty-five years ago, where it is one of the few common trees that is not a dipterocarp.

Unding Jami of SEARRP with a belian in Danum Valley, Sabah, on the walk out from the field station to Menara. Menara is a dipterocarp, a yellow meranti, and at 100.8 metres the tallest tree in the tropics. For a few years everyone was competing over measuring the biggest one, and Unding is the climber who settled it with a tape in 2019 (Shenkin et al. 2019). This one is a belian.

We know belian lives more than a thousand years because someone carbon-dated it. In 2003 Hiroko Kurokawa and colleagues radiocarbon-dated wood from fifteen logged belian stumps in Kubah National Park, a small park behind Kuching in Sarawak (Kurokawa et al. 2003). The innermost sound wood of a 121-centimetre stump came out at 838 years old, and the tree had a rotten heart beyond that, so the whole tree was older still. Across the stumps the wood had thickened by roughly a millimetre of diameter a year. A belian you can just get your arms around has been there for several centuries.

A belian seed. They are seven to fifteen centimetres long. Photo: Unding Jami, SEARRP.

The same paper compared the ages of belian and dipterocarps. The estimated lifespans of dipterocarps at full size ranged from 60 to 570 years. The growth rate of belian was among the very slowest of them, and its lifespan was well beyond any. Kurokawa's group suggested the tree may keep fruiting for 800 years or more, and put the long life down to the density of the wood and the defensive chemistry inside it. Part of that chemistry has adopted the tree's name: eusiderin, a compound isolated from belian heartwood in 1960 (Hobbs and King 1960). It is a life history strategy: grow slowly, build wood that nothing can eat, and outlast everything around you.

Growth that slow has a consequence for anyone hoping to replace what was cut. Seedlings in the shade of a closed forest hardly ever die, but they hardly grow either. Opening the canopy around a five-year-old seedling roughly trebles its growth (Kiyono and Hastaniah 2000). Even so, a trunk 30 centimetres across is a matter of a century, which is why nobody has ever built a belian plantation at scale. Restoring a logged forest is slow for the same reason, and a synthesis of restoration outcomes across tropical Asia shows what actually works.

Why belian wood is so dense

Dense wood is stored carbon. Two trees of the same size can hold very different amounts of it, and belian is at the heavy end. That is why mapping carbon across Malaysian Borneo means measuring more than canopy height. Measured on planted trees in Sarawak, belian's basic density is about 0.86 grams per cubic centimetre, the same from the centre of the trunk to the bark (Aiso-Sanada et al. 2020); the US Forest Products Laboratory gives 0.86 to 0.92, which works out at about a tonne per cubic metre once the timber is air-dry (USDA Forest Products Laboratory). So belian is a sinker, not a floater. It is also hard enough that a team wanting to core belian trunks in Sabah for growth rings had to design a new drill first (Williams et al. 2015).

In the Global Wood Density Database, the reference set ecologists use to turn tree size into carbon, belian's records sit between 0.71 and 0.84. That puts it in the densest tenth of South-East Asian trees, and denser than the great majority of dipterocarps, whose median is around 0.61. But a few of them, the balau group of Shorea and several Hopea, are just as heavy, and they sink too. What sets belian apart is not that it is the densest wood in the forest. It is that it is very dense, very durable and very old at the same time.

Seeds and seedlings of the belian tree

Each fruit holds a single seed, between seven and fifteen centimetres long, with a ridged coat almost as hard as the timber (Soerianegara and Lemmens 1993). No other tree in Borneo drops a seed like it, so sometimes you find the seed on the ground and then look around for the tree. The IUCN assessment suggests the seeds were once moved by large mammals, some of them no longer in the forest, and that they also travel by water, which is why belian is so often found along river banks (IUCN 2025).

Removing a lot of adult trees has implications for the next generation. In a four-hectare plot of old-growth forest at Maliau Basin in Sabah, Lan Qie and colleagues found fewer young belian than the adults should have produced, clumped rather than spread, and heavily browsed. Seedlings were heavily browsed, with sambar deer the likely culprit, and the losses were density dependent: the more seedlings in a patch, the larger the share eaten (Qie et al. 2019). Qie and her colleagues concluded that keeping the species going will take conservation effort aimed at belian itself, not only at the forest around it.

How to recognise a belian tree

The tree can be recognised by its pitted, pocked, greyish-brown bark. The leaves are simple and elliptic, set in a spiral up the twig rather than in opposite pairs, and a new flush comes out red (Sarawak Forest Department).

Where belian grows

This is a tree of the lowlands. It grows in Borneo (Sabah, Sarawak, Brunei and Kalimantan), in eastern and southern Sumatra and its islands Bangka and Belitung, and in Palawan and the Sulu archipelago in the Philippines (Kew; IUCN 2025). It is a lowland rainforest species, found from near sea level to about 650 metres (Yudaputra, Fijridiyanto and Cropper 2020), on a range of soils, usually scattered through mixed dipterocarp forest at a few trees per hectare, though it can cluster and in places dominates the canopy. While it has been heavily logged, it can persist in old secondary forest.

Where belian has been recorded: occurrence records for Eusideroxylon zwageri from GBIF, retrieved 11 September 2026. Hillshade highlights that the records tend to sit in the lowlands, not on the mountains. Cultivated trees outside the native range are excluded, and only records released under CC0 or CC BY are used. GBIF holds only a handful of century-old herbarium specimens from the Philippine part of the range (Tawi-Tawi, 1910 and 1911) and none with coordinates, so Palawan and the Sulu islands are blank here despite belian being native there.

The range is wide. The population inside it is not what it was. Sumatra's belian was described as almost entirely destroyed as long ago as 1994 (WWF and IUCN, Centres of Plant Diversity), and in Borneo the tree is now most reliably found inside protected areas: Danum Valley, Maliau Basin and Imbak Canyon in Sabah, Kubah in Sarawak, and a string of reserves in Kalimantan.

The timber: belian wood and what it is used for

The timber is the reason everyone knows the tree. It is rated in the top durability class: more than fifty years in the open, more than fifteen in contact with the ground, and effectively immune to termites (ITTO). Even the narrow band of sapwood resists decay, which almost no other timber manages; Andrew Wong's group at the Forest Research Institute Malaysia spent years working out why (Wong and Singh 2001). What eventually gets into belian is bacteria, slowly, in wet ground: tunnelling bacteria that bore through the cell walls, first shown under the electron microscope in 1992 (Nilsson, Singh and Daniel 1992).

Reclaimed belian. The weathered surfaces have gone grey; the fresh cuts are orange-brown. These boards came out of old structures in Borneo and are still sound.

So people build with it, and have for as long as there have been longhouses. In Sarawak and Kalimantan the main posts, beams and stilts of a Dayak longhouse are belian, and so are the roof shingles. A belian house post is expected to outlast the house. It goes into jetties, piers, wharves and bridges, and into boats; the Sarawak Forest Department lists longhouse structure, furniture and the posts that pepper vines climb. It has long been valued as coffin wood. In Danum Valley there are belian coffins lodged on ledges of a limestone cliff above the river, carved with animal heads and reputed to be at least 250 years old, still whole in the open air. For the Berawan of Sarawak the tree is a cultural keystone, used in burial rites and carved into posts (Franco et al. 2014).

What belian wood costs, and why

The timber has always been expensive, and the official numbers suggest around ten times the rate for other timbers. Sabah charges an export levy (it calls it a cess) of RM 100 per cubic metre on belian sawn timber against RM 10 for sawn timber of any other species, and the royalty on converted belian, meaning sawn or otherwise processed timber, runs at more than double the general rate (Sabah Forestry Department schedules). Those are state fees rather than market prices, but they are set against what the timber is worth, and belian is the only species the levy singles out by name. The deeper reason is supply: a century to reach thirty centimetres across, no plantation at scale, and legal felling restricted almost everywhere it grows. Most of what you can buy today is reclaimed rather than newly cut.

How to identify belian wood

Four things give a belian board away. Weight is the first, and the most reliable: at around a tonne per cubic metre air-dry it is heavier than nearly anything it could be confused with, and an offcut dropped in water sinks. Colour is the second. A fresh cut is yellowish, sometimes faintly olive, and it darkens on exposure to deep reddish brown and eventually close to black (Commercial Timbers). Old surfaces left outdoors can weather to grey while the wood underneath stays sound, which is the contrast in the photograph at the top of this section. Sapwood is the third: a narrow, distinctly paler band at the edge. Insect damage is the fourth, because of its absence. Termites and borers leave belian alone, so a hundred-year-old beam full of holes is something else. Freshly cut belian is also often described as faintly lemony, which would fit a family that includes camphor, cinnamon and bay.

Finished belian wood: fine, even grain running straight along the board, and the olive-brown the heartwood settles at.

Why belian is Vulnerable: logging and conservation

The qualities that make belian a good post made it the first tree to go. Loggers took the most valuable stems first, and belian was the most valuable. The species is listed as Vulnerable on the IUCN Red List, first in 1998 and again in the 2025 reassessment, which suspects a decline of more than 30 per cent over the last three generations, about 300 years for a tree like this, from timber extraction, poor regeneration and the loss of lowland forest to agriculture (Barstow 2025).

People in Borneo have carefully cut belian for houses and boats for centuries, and in West Kalimantan villages had their own rules about who could take it. That use did not endanger the tree. Chainsaws, logging roads and the clearing of forest for timber estates and oil palm did, and the customary rules were never recognised by the state (Peluso 1992).

The belian we named the company after, in logged forest in Sabah. The bole is hollowed and split, which is exactly why it is still standing: loggers took the sound, straight stems and left the defective ones. A lot of the belian you find in a logged forest is there because it was not worth cutting.

The law now varies by border. In Sabah, belian is a prohibited species under the Forest Enactment 1968: it may only be felled in special circumstances such as unavoidable road building or a tree already damaged (Sabah Forestry Department). Sarawak has controlled belian export since the 1950s. Indonesia protected the tree for decades, then recently took it off the protected list, and logging has picked up again (IUCN 2025).

There is a carbon lesson in all this. Often, the trees that logging removes first are the ones that hold the most carbon for the longest. A forest's carbon cannot be measured by area alone, and what was extracted over a century ago still shapes what is standing now. That is the problem our baselines are built to handle, and part of why restoring logged forest matters so much in Borneo. Whether a project protecting forest like this can sell credits at all is decided by the integrity bar the ICVCM sets, and whether a company may count them against its own targets is decided by the SBTi's corporate net-zero standards.

Upcycled belian and Kaltimber

Because belian does not rot, a beam pulled out of a bridge that went up a century ago is still sound timber. That makes upcycling worth far more for this species than for most. A tree takes a hundred years to reach thirty centimetres across and the species is Vulnerable, so reclaimed belian, or kayu ulin as it is called in Indonesia, is the only supply that does not cost a living tree.

The best example I have seen is Kaltimber, who work in nothing but reclaimed ulin and turn it into decking, flooring, furniture and homewares. I have had two tours of their place in Bali and I own some of what they make.

What reclaimed belian looks like before anyone touches it: salvaged beams in the yard at Kaltimber, still carrying the bolt holes from whatever they held up.

Kaltimber are at Batuan in Gianyar, a few miles south of Ubud. The Balinese are known for their craftsmanship and for their woodworking in particular.

The sign on the road at Batuan, south of Ubud. One species, and none of it newly felled.

What Kaltimber do is bring that tradition together with a modern mill and a commitment to work only with reclaimed ulin. They take old bridges, boats, jetties and warehouses that have been abandoned and cut them carefully into large, sound pieces of timber that can be used again in buildings. Most of it becomes decking and parquet flooring to a very high standard. They also make furniture and woodware, much of which ends up in Bali's hotels, where there is a real push to make tourism more sustainable.

A salvaged board going through the mill. The timber is hard enough that milling it is slow work.

They are good at making sure nothing goes to waste. Boards are sorted and marked by size so that offcuts stay usable, smaller pieces become homewares, and the smallest offcuts of all are turned into beads. I wore a strand of belian beads at the World Economic Forum in Davos, next to a togetherband.

Offcuts become homeware. This one is ours: a coaster cut from reclaimed belian, with the mark burned in. The fine speckling is the wood's own pore pattern.

Everything they work with is reclaimed and they mill no new ulin at all. Their stock is certified under SVLK, Indonesia's timber legality system, and the homewares made from offcuts go out under their own i-Rewood name.

Finished reclaimed ulin. The timber in this table is older than the building it will stand in.

Other things called belian

In Malaysia and Indonesia, belian is an everyday word, so it lands on a lot of different things. On its own it can mean a purchase. As an older word it meant a shaman, and among Dayak communities in East Kalimantan a belian is still a healing ceremony. In Iban it is a diamond. Kampong Sungai Belian is a village in Sarawak, and a number of Malaysian and Indonesian businesses use the name, because in those languages it is simply a word. All of that is set out in what the word belian means.

Outside the region, the mobile game Epic Seven has a character called Belian, which is why searching the bare word returns so many game pages. This page is about the tree, and about belian.earth, the company named after it.

References

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Forest carbon markets face a fundamental credibility challenge: how do you estimate what would have happened without a conservation intervention? Recent high-profile analyses have questioned whether existing carbon baseline methods deliver accurate results, a debate our team has contributed to directly through our critique of synthetic control approaches in Science.

This six-month feasibility study will let us systematically test emerging techniques in geospatial machine learning and causal inference against this problem, with a focus on quantifying uncertainty in counterfactual estimates.

Our team brings more than two decades of field research in tropical forests, including work published in Science on carbon recovery rates, combined with operational experience in forest carbon project development and assessment. We also bring extensive expertise in cloud computing and open-source tools for reproducible ecological workflows. ESA's support lets us bridge that applied research background with new computational approaches.

We'll be sharing methods and findings openly as the work progresses. Our aim is to contribute tools that make rigorous counterfactual baseline assessment more accessible across the sector.

More detail on the work, the data behind it and where it is heading is on our Conservation Integrity page.