'Stop and think' calls about BrewDog-like tree planting schemes in Highlands for net zero goals

Researchers found that carbon stored in trees that grew from naturally dispersed seeds on heather moorlands in the Cairngorms did not outweigh the carbon lost from disturbed soil

A peat expert has urged Scotland to have a rethink when it comes to trees in the upland landscape following new research that throws the carbon capture benefit of natural regeneration on moorland into question.

Natural tree colonisation may not always produce carbon capture benefits, study finds | JHI

In a new study, led by the James Hutton Institute (JHI) in collaboration with the University of Edinburgh and Forest Research, scientists examined native trees growing naturally on heather moorlands in the Cairngorms.

These trees established themselves without human intervention, growing from seeds dispersed by nearby parent trees. However, after 25 years, scientists found the carbon stored in the trees did not outweigh the carbon lost from the disturbed soil in the growing process, leading to no net carbon capture.

Previous research by the JHI and the University of Stirling found that actively planting birch and Scots pine trees in heather moorland eco-systems with carbon-rich soils was linked to soil carbon losses that were similar to the amount of carbon captured in the trees. This meant no net carbon was captured in the first few decades after tree planting.

Lorna Street, a lecturer at the University of Edinburgh’s school of geosciences, said: “It’s easy to assume that creating a new woodland will always have a carbon benefit, because we see carbon being stored as the trees grow. Our work shows that carbon losses from soil can cancel out those benefits, even when soils are not physically disturbed by planting.”

Peat expert and ecologist Dr James Fenton said he was not surprised by the JHI paper’s conclusion.

Dr James Fenton, peat expert and ecologist | Dr James Fenton

“To me, the conclusion here should have been obvious,” he said.

Dr Fenton said it has been known for years following Forestry Commission research in the Flow Country - a vast area of bog peatland the Highlands - that planting trees on deep peat causes the peat to dry out and to release the stored carbon – more than is stored in the trees themselves.

With the existing policy of no planting on deep peat, he said most tree planting was, instead, happening on areas with shallow peat, which can be found under heather moorlands.

He said: “Peat obviously does not start off ready-formed, but starts developing on humus-rich soils before developing into shallow peat, and eventually into deep peat. But deep peat is vulnerable to erosion, which releases the carbon.

“However, the current policy of not planting trees on deep peat means that most tree planting in the uplands is directed towards shallow peats and humus-rich soils, such as is found under heather moorland.

“But for the above reason, from a climate perspective, this must be the worst thing to do, because such soils, as they deepen over the millennia, have the best long-term carbon storage potential of any terrestrial habitat.

“The recent paper from the JHI is referring to naturally regenerating trees. But, from a climate perspective, it will make no difference whether the trees have been planted, or put themselves there. Hence the researchers’ conclusions should not be particularly surprising.”

He said where soils contain little soil carbon, as in much in the lowlands, then tree planting may be beneficial.

The JHI research involved studying five sites in the Cairngorms where Scots pine and birch trees had naturally colonised heather moorlands. Measurements of carbon levels in the trees, soil and heather revealed that carbon stocks in the organic layer of the soil - the layer where most carbon is stored - were reduced by 50 per cent near the base of the trees compared with open areas of heather moorland.

Thomas Parker, an upland ecologist at the JHI, stressed the consistency of the findings across the sites and called for further large-scale studies to determine if similar patterns occurred in other soil types and climates.

Dr Fenton said the research should lead to more questions about the Scottish Government’s policy of more tree planting “because everyone just goes along with it”.

“I think it’s time to take stock,” he said. “We have new results coming in on the knowledge of the vegetation history of the Highlands and Scotland over the last several thousand years, and new research on grazing and on carbon storage.

“We need to stop and think about what we’re doing because there’s a lot of evidence out there.”

Both forms of establishing trees, whether it is through planting or natural regeneration, are pursued by a various landowners from private companies to trusts to NGOs using public funds from the Scottish Government’s Forestry Grant Scheme (FGS).

The FGS is part of ministers’ plans to achieve net zero carbon emissions by 2045.

One grant beneficiary is BrewDog, which took over Kinrara, an upland estate in the Cairngorms, to establish the “single biggest native woodland establishment and peatland restoration project ever carried out in the UK”.

The purchase was motivated by “becoming the world’s first carbon negative beer business”, with a claim the company is “removing twice as much carbon as we emit every year, forever”. Last year, however, the company admitted half of the saplings planted for its million tree Lost Forest died in the first year.

When asked about the beer giant’s scheme, Dr Fenton claimed the company’s claims of restoring biodiversity were in fact “destroying” the land.

“Whether it’s a personal view, it’s [planting] taking it away from one of the most natural landscapes remaining in the world,” he said.

BrewDog’s former chief executive James Watt had blamed the tree deaths on the weather, saying “extreme conditions resulted in a higher-than-expected failure rate”.

The JHI researchers said although natural tree regeneration may not always deliver immediate carbon capture benefits, it could still be a valuable tool for increasing tree cover and providing other environmental and social benefits.

Naomi Housego, postgraduate researcher at the JHI, who led the research, said: “Trees can also be established for other benefits such as increased biodiversity, flood alleviation or recreation.

“Given that overall we found neither carbon gains nor losses, natural colonisation could still provide an approach for increasing tree cover that provides these eco-system services.

“Nonetheless, we must consider the potential for soil carbon losses when increasing tree cover with the aim to capture carbon.”

A Scottish Government spokesperson said: “Restoring Scotland's natural environment is vital to tackling nature loss and climate change.

“Research commissioned by Scottish Forestry has examined the carbon benefits of planting different types of woodland and provides a sound evidence base to underpin woodland creation plans. Rules on peat planting have also been tightened across Scotland and are reflected in the UK Forestry Standard and associated guidance, meaning new forests should not be established on deep peat where the peat layer is deeper than 50cm.”

BrewDog has been contacted for comment.