A North American tree that kills native species and threatens protected habitats vital to fight climate change now makes up nearly half of Scotland’s forests, The Ferret can reveal.
Our analysis of official forestry data shows that Sitka spruce makes up 43 per cent of Scotland’s woodlands, more than triple that of Scotland’s national tree, the Scots pine.
As well as crowding out and killing native species, Sitka spruce “self-seeds” in important habitats such as peat bogs, risking the release of vast amounts of carbon the bogs have absorbed.
NatureScot’s assessments, obtained by The Ferret via freedom of information, found “invasive” Sitka spruce have had a “negative” impact on protected bogland and heathland, including in the Trossachs national park.
An area of peatland collectively larger than twice the size of Fife is at higher risk of being impacted by self-seeding trees, according to the wildlife agency. Some scientists and conservationists also warn the species is rapidly “colonising” native woodlands and sensitive areas.
The trees have been removed from the ancient Caledonian Forest after killing Scots pines.
But forestry bodies said it was unhelpful to “demonise” Sitka spruce, which, they argued, absorbs carbon quickly, is key to Scotland’s woodland growth and net zero targets, supports 25,000 jobs, contributes £1bn to the economy and reduces the need to import timber.
Since being first planted in Scotland in the early 1800s, the fast growing and resilient tree has thrived in Scottish climate conditions and soils, and become important for the forestry sector.
Industry figures insisted commercial forestry is managed sustainably and the proportion of native trees in Scottish woodlands was on the rise.
Sitka spruce ‘colonising native habitats’
NatureScot’s assessments list Sitka spruce as having a detrimental effect on protected bog and heathlands. These include Loch Macanrie Fens in the Trossachs national park, Craigengar in the Pentland Hills, Loch Etive Woods, which stretches from in Argyll to the Highlands, and Dumbarton Muir.
The tree’s impact has left Lon a’ Chuil in Sutherland and Knockdaw Hill in South Ayrshire in “unfavourable” conditions.
According to State of Nature’s 2023 report, which NatureScot deemed “the most precise review of how nature in Scotland is faring”, Sitka spruce is “increasingly colonising neighbouring habitats”.
The tree spreads by dispersing its own seeds, which have reached “sensitive areas” including peat bogs, grassland, and moorland, overpowering other species and reducing these habitats’ abilities to capture carbon.
Self-seeding trees risk sucking water from peat bogs, which release carbon they have absorbed as they dry. An estimation of how much carbon self-seeding trees absorb compared to how much is released from the peat bogs they impact is not known.
NatureScot predicts that 846,000 hectares of peatland are at risk of seeding from nearby tree plantations, and for 267,000 hectares – more than twice the size of Fife – the risk is high.
It’s not helpful to demonise one species of tree against another.
Scottish Forestry spokesperson
Conservation charity John Muir Trust removes “invasive non-native species” such as Sitka spruce from its land to help native species regenerate.
Sitka spruce’s “dominance in Scotland is “definitely problematic”, claimed Rosemary Simpson, the trust’s senior policy officer. “The dense planting of a spruce plantation shuts out light, preventing plants from growing on the forest floor.”
Government agency Scottish Forestry says Sitka spruce absorbs CO2 “many times faster” than broadleaf trees.
But Dr Ruth Mitchell, plant soil ecologist from the James Hutton Institute, warned that more carbon may be released by disturbing soils during planting than can be absorbed by the trees for decades.
“We also need to take account of the full life cycle of the wood – using timber for wood pulp, paper or even biofuel can mean that carbon is not stored for long enough to contribute to government net zero goals,” she told The Ferret.
Last year, the chair of the Dumfries-based Crichton Carbon Centre charity argued that Scotland has been “planting the wrong type of forests, in the wrong place, and using the wrong techniques”, with ”most” forestry planted on peat.
A ‘great tree’, but ‘poorly managed’
Willie McGhee, a forest owner and manager who sits on the board of the Forest Policy Group think tank, describes Sitka spruce as a “great tree” which makes “economic sense” for foresters to plant where other species cannot grow.
But the trade body Confor – “industrial forestry cheerleaders” – and woodland investment firms have encouraged “tree farming”, where Sitka plantations are unmanaged for 30-40 years before being felled for timber, he claimed. This method has “no local benefits” and serves only “wealthy absentees” – rich landowners who do not live locally – he argued.
“My issue is not with the tree. It’s where it’s used, how it’s used and how it’s not being managed – there’s often little or no forest management.” McGhee claimed he has seen Sitka growing in places as remote and inhospitable as on Skye’s Cuillin Ridge, and now deems the tree “a threat to our native forests and fragile habitats”.
“Foresters, and I include myself, didn’t think about the possible impacts of planting such a prolific and invasive species in potentially sensitive areas,” he added.
The release of invasive species is prohibited in Scotland, but Sitka and other commercial tree species are exempt because they are deemed important to the Scottish economy, and because it was believed their spread can be managed.
In New Zealand, the government fears invasive conifers will engulf a quarter of the country within 30 years without action. A plan is underway to remove trees that have spread outwith plantations.
My issue is not with the tree. It’s where it’s used, how it’s used and how it’s not being managed.
Willie McGhee, Forest Policy Group
A February report from the Royal Society of Edinburgh (RSE) called for Scottish Forestry to stop the spread of invasive species like Sitka, ban planting on carbon-rich soils with machinery, and require more diverse plantations.
Scottish Forestry should end the public funding of commercial conifer plantations, which includes grants and full tax relief on profits and capital gains, RSE argued. It should instead fund planting designed to store carbon long term, improve biodiversity, increase public benefits, and ramp up environmental assessments.
In 2021, the Scottish Government’s former chief planner said Scotland had accelerated its commercial timber industry by giving “full-blown” environmental checks to just two per cent of planting proposals since planning reforms were introduced.
A Confor spokesperson said: “The methodology and conclusions of the RSE’s report both have been widely critiqued by independent academics with long-standing expertise in forest and environmental sciences. The report’s analysis of the timber sector is particularly weak, with poor evidence and recommendations that do not stand up to scrutiny.
“Poorly prepared publications such as this run the risk of damaging the important forestry sector in Scotland and undermining efforts by the Scottish Government, industry, and academia to promote sustainable wood use and combat damaging climate change.”
‘Not helpful’ to ‘demonise’ Sitka
Both public and private forestry bodies defended the prominence of Sitka spruce.
“It’s not helpful to demonise one species of tree against another,” said a Scottish Forestry spokesperson. “Ultimately it doesn’t help decision making and creates polarised views which are detrimental in trying to increase woodland expansion across Scotland.”
When assessing applications to plant trees, the forestry body aims to create mixed and balanced forests – putting “the right tree in the right place” is its “overarching philosophy”, they said.
Half of the 14,000 hectares of recent woodland creation applications it approved will consist of indigenous species – “the highest level of native approvals for 20 years”, claimed the spokesperson.
“From October, all new woodland created in Scotland will only be allowed 65 per cent of a single species and that shall ensure there is diversity in our woodlands.”
Forestry and Land Scotland owns and manages around a third of Scottish forests on behalf of the nation.
A spokesperson for the government body said: “As custodians of some of Scotland’s finest native woodland sites, such as Glen Affric, Glenmore and one third of Scotland’s Temperate Atlantic Rainforests, we are fully engaged in protecting those unique habitats while at the same time engaging in sustainable commercial forestry.”
Confor said it “promotes the planting and sustainable management of all types of woodland” and had worked with others to produce government-approved forestry standards.
Commercial forests have “considerable benefits for biodiversity” due to their management, which is funded by the sale of high-quality timber, while woodlands that do not generate income are “often left unmanaged and in poor ecological condition”, it argued.
The proportion of Sitka in Scotland was “in decline even though it is a resilient tree that suits many growing conditions and produces a high-quality product”, the spokesperson added.
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That’s a tremendous piece of work.