Is robinia an ecological timber?
Robinia series · Understanding the material
What robinia genuinely does better than treated timber — and the three places where its record is not perfect.
Yes, on the essentials. Robinia (Robinia pseudoacacia) — also known as black locust, and often sold as acacia — reaches use class 4 (EN 335), meaning permanent contact with the ground or fresh water, without any chemical treatment. It grows almost everywhere in Europe, but its heartland is Central and Eastern Europe: in Hungary and Romania it forms genuine managed forests, around 2,000 km from most of Western Europe. There, the forest regenerates on its own through root suckering — new shoots that spring from the roots — with no replanting. And one cubic metre of robinia put to use keeps around 1.3 tonnes of CO₂ out of the atmosphere for the whole life of the structure.
Three caveats remain, and we would rather raise them ourselves: transport is still a significant item, finger-jointed boards contain adhesive, and robinia is an introduced species in Western Europe whose place outside managed forests is debated. Here is the full assessment, strengths and limits.
≈ 1.3 tonnes of CO₂
stored in one cubic metre of robinia put to use — and locked away for as long as the structure lasts
No treatment: what that really changes
Robinia heartwood — the dark core of the wood — is rated class 1 to 2 on the natural durability scale of EN 350, the highest level. It is the only European hardwood that can be used in use class 4 without any biocide at all. The durability is in the body of the wood, not in an applied layer: cutting, drilling or notching on site opens no weak point.
The useful comparison is with pressure-treated pine, the other way of reaching use class 4. Pressure treatment forces copper salts into the sapwood — the soft outer part of the wood — to make durable a species that is not. The process works, but it produces timber that stays loaded with biocides throughout its life and becomes waste that has to be dealt with at the end. Robinia has nothing to inject, and therefore nothing to dispose of.
That is what makes the most sensitive uses possible. A debarked robinia stake is chemically inert: it is the timber for raised vegetable beds, for edging in contact with growing soil and for children's play areas, where no treated timber is accepted.
Carbon: how much, and for how long
One cubic metre of dry robinia weighs around 700 to 750 kg. Wood is roughly 50 % carbon: that gives some 350 kg of carbon per cubic metre, or about 1.3 tonnes of CO₂ that the tree removed from the atmosphere and that stays locked in the piece of timber. A stake, a decking board or a pergola post is, quite literally, carbon in storage.
So the interesting question is not how much, but for how long. A robinia stake lasts around 30 years in ground contact, against about ten years for a pressure-treated pine stake. For the same length of fence, that means storage three times as long, and three times fewer rounds of manufacturing, transport and replacement work. Durability is not just a cost argument: it is the core of the carbon argument.
At the end of its life, untreated wood gives back the CO₂ the tree captured, no more and no less — and it can do so usefully, as firewood. Pressure-treated timber, on the other hand, must never be burnt in a domestic stove or fire and goes into the waste stream.
One widely misunderstood point deserves to be made here: a tree left to rot in the forest releases exactly the same carbon as a tree that is burnt. Decay is slow combustion — fungi and bacteria oxidise the cellulose and lignin, and the CO₂ returns to the atmosphere within a few years. Harvesting a mature tree to make a stake or a decking board therefore does not release carbon that would otherwise have stayed in the ground: it delays its return by thirty years, while the plot captures more in the regrowth.
This is the whole difference between the short and the long carbon cycle. The wood cycle turns over a few decades: the tree captures carbon, the structure holds it, decay or combustion releases it, a new tree takes it up again. The carbon in a steel, PVC or concrete post, by contrast, comes from a fossil store locked away for millions of years: once emitted during manufacture, it enters no cycle and never comes back down. Replacing a concrete post with a robinia post is therefore not a like-for-like swap — it takes an emissions item out of the long cycle.
A forest that replants itself
Robinia regenerates through root suckering: after felling, the roots left in the ground send up new shoots, vigorous from the first season. No planting is needed, no soil is turned over, no seedlings are grown or transported. The plot closes over into a young stand within a few years and can be harvested again after 25 to 30 years.
Romanian rules frame this cycle: a maximum of three hectares per clear-cut, no felling of an adjoining coupe until the previous one has closed over, and harvesting while the sap is down, between September and March. Harvesting therefore moves forward in small windows that shift across the forest, never in whole blocks. The work in the forest is described in our article “Robinia forests in Romania – felling, brash windrows and root suckering”.
We also plant one tree for every cubic metre sold — more than 75,000 trees to date — on land that lacks them rather than in production forest, where nature takes care of it. Robinia fixes nitrogen from the air thanks to bacteria living on its roots: it grows where other species fail, on poor soils, embankments or old spoil heaps, which it begins to rebuild.
2,000 kilometres, not 10,000
Our timber travels around 2,000 km by road from the sawmill in Teiu, Hunedoara County (Romania), to most of Western Europe. A Brazilian ipe travels more than 10,000 km, most of it by sea.
To be precise: shipping emits little per tonne carried and per kilometre, so the gap in emissions between the two journeys is real but less dramatic than the ratio of distances suggests. The real difference lies elsewhere. A European timber under FSC® certification and covered by the EU Deforestation Regulation (the EUDR) can be documented plot by plot; a tropical timber involves primary forest whose traceability is far harder to establish — ipe has in fact been listed in CITES Appendix II since November 2024.
And we do not cover that distance any old way. Whenever lead time and destination allow, our shipments go by intermodal transport: the trailer is loaded at the mill, carried by rail for most of the journey, and only returns to the road for the first and last legs. The gain is directly a carbon gain — according to the European Environment Agency, rail freight emits nearly three times less CO₂ per tonne-kilometre than road freight — and it costs the goods nothing, as they stay in the same trailer from start to finish. Not everything can go this way: an urgent order, a remote site or a small volume goes by direct lorry. On our regular routes to France, Belgium and the Netherlands, intermodal is our preferred mode; for any other delivery, lead time, volume and destination decide.
A honey tree: the timber and the honey come from the same tree
Robinia flowers in May, in highly scented white clusters, and it is the source of so-called “acacia” honey. Hungary and Romania are Europe's leading producers, with apiaries set up in the same forests that supply the construction timber. Beekeepers there practise migratory beekeeping: the hives travel on trailers and move from the south to the north of the country as spring advances, because the south is warmer and flowering starts two to three weeks earlier there. A single colony can thus follow the wave of blossom from one forest to the next. And harvesting in small, staggered coupes maintains a mosaic of age classes — and therefore stands in flower every spring — where management in large blocks would wipe out the honey resource for years.
An introduced species: the point to address honestly
Robinia arrived from North America in 1601, planted in Paris by the botanist Jean Robin, who gave it his name. Four centuries later, it is naturalised across almost all of Europe, and its spontaneous spread raises genuine ecological questions: its ability to fix nitrogen enriches poor soils, which is an asset on an embankment and a problem on dry grassland, a rare habitat that depends precisely on poor soil.
The facts, without dressing them up: robinia is an introduced species, and its spontaneous spread is monitored in several European countries. In Romania and Hungary, by contrast, it has been a cultivated forest species for more than two centuries, in dedicated stands included in forest management plans. Our timber comes from those forests: harvesting it keeps it within a managed framework rather than establishing it somewhere new. The question of whether you should plant it yourself is covered in our article “Robinia forests in Romania – felling, brash windrows and root suckering”.
A voice from the field is worth more than a plea. Cătălin Tobescu, director of Fordaq in Romania and manager of more than 3,000 hectares of robinia in the south of the country, along the Danube, is a respected voice in the Romanian forestry sector. This summer he posted a photo of a salcâm plantation — the Romanian name for robinia — established the previous spring on the sands of southern Oltenia, as part of a project under the national recovery plan.
“A remarkable species, with spectacular successes on these sands, in these extremely dry years,” he writes. A reader immediately raises the expected objection: “For the grumblers, an invasive species.” His reply takes three sentences: “Correct. It can invade the sands. How good it would be if these projects were continued and extended, in a targeted way, where the need is real — and if we helped robinia invade these sands.”
This is the point we made above, put by someone who plants: “invasive” is not a property of the tree, it is a relationship between a species and a habitat. On calcareous dry grassland, robinia is a problem, and that needs saying. On shifting sand in southern Romania, after several years of drought, it is one of the few species that holds — and its ability to fix nitrogen becomes a service to the soil. The same tree, two opposite verdicts: the habitat decides, not the species.
Where our record is not exemplary
Transport remains our largest source of emissions, and the last mile is by road, on diesel: for pallets of stakes delivered to scattered sites, there is no credible alternative today. Where intermodal is used, it lightens the longest part of the journey, not all of it — and it requires lead times that not every order can accommodate.
Finger-jointed decking boards and joists contain a structural adhesive (finger-jointing to DIN 68140, class C4 adhesive to EN 12765). It is not bio-based. It does, however, have a direct justification: finger-jointing joins short pieces end to end that would otherwise go for fuel — it is what makes it possible to get 6 m lengths from a naturally crooked tree.
Material yield is low. Robinia rarely grows straight: a large share of each tree will never become a board. Nothing is wasted — crooked stems become stakes, sawmill offcuts become firewood and wood chips — but it takes more trees to produce a cubic metre of sawn timber than in a pine plantation.
On formal guarantees, our timber is covered by FSC® certification (licence C153588, chain of custody SGSCH-COC-011793; FSC® 100 % on request) and by SUMAL, the Romanian forest traceability system, on which our declarations under the EUDR are based.
Key points
· Use class 4 (EN 335) with no treatment at all: the durability is in the body of the wood — nothing to inject, nothing to dispose of.
· Around 1.3 t of CO₂ stored per m³ — and, above all, stored three times as long as with pressure-treated pine.
· Wood belongs to the short carbon cycle: a tree rotting in the forest emits as much as a tree that is burnt, whereas steel, PVC and concrete release fossil carbon that never comes back.
· Natural regeneration by root suckers: no planting, no soil preparation; clear-cuts of 3 ha maximum, 25- to 30-year rotation.
· Around 2,000 km from Romania to most of Western Europe, by intermodal rail-road transport wherever possible, under FSC® certification and covered by the EUDR — against more than 10,000 km for a tropical timber.
· The limits we acknowledge: the last mile by road, the adhesive in finger-jointed products, and a low material yield.
Frequently asked questions
Does “untreated timber” mean no chemicals at all, even in finger-jointed boards?
For solid timber, yes, without reservation: stakes, posts, boards, cleft palings and shingles receive no biocide, no fungicide, no metal salts and no pressure treatment — the tree produces its own durability. For finger-jointed products — decking boards, cladding and joists — there is one exception you should know about: the pieces are joined end to end with a structural adhesive of class C4 to EN 12765, the class that withstands outdoor moisture (the finger joint itself follows DIN 68140). This adhesive is a tiny fraction of the mass and stays confined to the joints, but it is there, and we would rather say so than write “100 % natural” on a glued range.
Can robinia be burnt or composted at the end of its life?
Burnt, yes: having received no treatment, it behaves like any other firewood and simply gives back the carbon the tree captured. It is an excellent fuel — the subject has its own article, “Is robinia good firewood? – myths and facts”. Composting it, on the other hand, makes little sense: its natural resistance to rot, the very thing that gives it its service life, makes it very slow to break down. The best end of life for a piece of robinia is still reuse — a stake that has been pulled out can be recut, a post can be reused — followed by use as fuel. Pressure-treated timber, by contrast, must never go on a domestic fire.
Is 2,000 km by road still a short supply chain?
No, and we do not present it as one. A short supply chain would be a sawmill a hundred kilometres from the site. What we claim is something different: a European timber from mapped and certified forests, which involves no tropical forest and where every lorry is documented. If you can source robinia from closer to home in the quantities and lengths you need, it will beat ours on transport. It is precisely because such closer sources are not enough for the volumes and long lengths demanded all year round that we source in Romania.
Does acacia honey come from the same tree as your stakes?
Yes, exactly the same one: Robinia pseudoacacia, sold under the name acacia. Acacia honey, pale and runny, is produced from its May flowering, mainly in Hungary and Romania, often in the same forests that supply construction timber. The two uses do not compete, they complement each other: a forest harvested in small, staggered coupes always has stands of different ages, and therefore trees in flower every spring.
Further reading
Reference guide: “Robinia outdoors – the complete guide”.
See also: “Robinia forests in Romania – felling, brash windrows and root suckering” · “Traceability of Romanian timber – SUMAL, APV and the EUDR” · “FSC and ISO 9001 – Acacia Bois certifications” · “Robinia or pressure-treated pine (use class 4) – the comparison” (treated versus untreated).
Our products: Round stakes · Square posts · Finger-jointed decking board · Finger-jointed cladding board · Cleft palings.
Contact: A project that has to justify its environmental choices? Tell us about it: we will send you the relevant certificates, traceability and transport data.
Disclaimer. Non-contractual article, provided for information only (photos and drawings included). Robinia is a natural material: the values given are orders of magnitude and may change without notice; in case of discrepancy, only the product’s technical data sheet and the general terms of sale apply. Always check the regulations that apply to your project.
© Xylo Impact SRL — all rights reserved, products marketed under the Acacia Poles brand. Any reproduction, even partial, is prohibited without prior authorisation.
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