Enhanced rock weathering lifted carbon storage 27% in Welsh reforestation trial, Imperial College London study finds

Applying crushed silicate rock to soil before planting raised aboveground carbon storage by 27 percent in broadleaf woodland after four years, according to a study led by Imperial College London and the charity The Carbon Community, published in Communications Sustainability on June 30, 2026. The Glandwr Forest Carbon Study, run on a former sheep pasture in Carmarthenshire, Wales, is among the largest and most highly replicated field trials to test enhanced rock weathering and soil microbiome enrichment for reforestation, according to the study’s authors.

Researchers, led by corresponding author Dr. Bonnie Waring of Imperial College London, planted more than 25,000 native trees across 72 plots covering 11.5 hectares beginning in 2021, testing two interventions, alone and combined, across both broadleaf and conifer stands. “What makes this study scientifically striking is not only the potential for carbon removal, but also its unprecedented scale, and the high level of citizen science involvement,” Waring said, as reported by Forestry Journal. “After just four years, we can demonstrate how each of these simple, nature-based interventions effectively supports the early years of tree establishment and the carbon uptake capacity of new woodlands.”

What the trial tested, and what it found

The study compared two interventions against untreated control plots: enhanced rock weathering, in which crushed basaltic andesite rock, a quarry byproduct, is spread on the soil surface before planting; and microbiome enrichment, in which soil taken from an established forest is added to tree roots at planting to introduce beneficial microorganisms. Both were tested alone and in combination, across native broadleaf species (alder, aspen, downy birch, wild cherry, sessile oak and rowan) and a Sitka spruce conifer monoculture, with growth and carbon storage tracked annually from 2021 through 2024.

The 27 percent figure applies specifically to broadleaf stands: rock-weathering-treated plots stored an extra 787 kilograms of carbon per hectare by 2024 compared with untreated plots (3,705 versus 2,917 kilograms of carbon per hectare), a gap that widened steadily each year of the trial. The study found the whole-plot carbon effect from rock weathering in the conifer stands was not distinguishable from chance, even though it boosted growth of individual conifer trees. Microbiome enrichment increased broadleaf aboveground biomass by 13 percent by 2024, though The Carbon Community’s own results page states that gain could not be distinguished from chance given high variability in tree growth across the site; the microbiome effect was strongest in the trial’s first year, when inoculated saplings grew 45.7 percent more than untreated ones, before narrowing over time. Combining both interventions produced no additional benefit to growth, survival or carbon storage over the four-year period, the study found.

Source: Waring et al., Communications Sustainability, June 30, 2026; The Carbon Community, “Glandwr Forest Carbon Study” findings page.

The volunteer count is one of a handful of small discrepancies between the peer-reviewed paper and the charity’s own materials: the journal article’s acknowledgements credit “over 290 volunteers,” while The Carbon Community’s own results page and Forestry Journal’s coverage both cite “around 200.” Press coverage has also generalized the 27 percent and 13 percent figures as applying to “reforestation” broadly; the study itself restricts both effects to broadleaf stands specifically, since neither intervention’s whole-plot carbon effect in the conifer plots was distinguishable from chance.

Citizen science and next steps

The trial relied on volunteers from The Carbon Community’s community science programme, who helped measure roughly 6,400 individually barcoded trees each October in an event called the “Big Tree Measure.” Charles Nicholls, co-founder of The Carbon Community, said the findings arrive as pressure grows to scale up viable reforestation methods. “These findings come at a critical time when we must rapidly invest in effective solutions that can tackle both the climate and biodiversity crises,” Nicholls said, according to Forestry Journal. Professor David Beerling of the University of Sheffield, whose Leverhulme Centre for Climate Change Mitigation contributed to the rock-weathering analysis, said further results are still to come: “These initial findings are just the start, with future results investigating the impact on belowground organic and inorganic carbon. We hope others will be able to replicate these interventions to make a considerable difference to carbon removal efforts.” The rock-weathering approach builds on related research into using crushed silicate minerals for carbon removal, an approach covered in prior reporting on carbon removal through enhanced rock weathering; the trial’s broader aim of quantifying verified carbon gains also bears on how such projects are counted and traded, an area explored in an overview of voluntary carbon markets.

About The Carbon Community

The Carbon Community is a UK-based charity focused on closing knowledge gaps around how much carbon trees and soil can realistically remove from the atmosphere. It established the Glandwr Forest field trial on a former sheep pasture in Carmarthenshire that had been grazed for at least a century before planting began in 2020 and 2021, in partnership with Imperial College London, the Royal Botanic Gardens, Kew, the University of Sheffield, ETH Zurich and the University of Edinburgh. The organization has run annual “Big Tree Measure” citizen science events at the site since planting, and its four-year results, published alongside the peer-reviewed study, mark the first major published output from the trial, with the authors saying belowground carbon data from the same plots is still to be analyzed.

Sources: Communications Sustainability (Waring et al., 2026); The Carbon Community; Forestry Journal

Featured image: photo by Raymond Petrik on Pexels (free Pexels license).

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Figen Sekin

I specialize in sustainability education, curriculum co-creation, and early-stage project strategy. At WINSS, I craft articles on sustainability, transformative AI, and related topics. When I’m not writing, you’ll find me chasing the perfect sushi roll, exploring cities around the globe, or unwinding with my dog Puffy — the world’s most loyal sidekick.