In 1961, a four-hectare field on the southern edge of an ancient woodland called Monks Wood in Cambridgeshire produced its last crop of barley. Having originally been cleared of trees during the Roman occupation, it was then abandoned to nature.
In the intervening 60 years, that field has changed beyond recognition. Today, it’s a mature, closed-canopy woodland with oak, maple and ash trees, as well as berry-bearing shrubs such as hawthorn and brambles.
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Its “structural characteristics”, according to a study published in the renowned science journal PLOS One in 2021, are “approaching those of neighbouring ancient woodlands”. That’s some recovery in a little over half-a-century – with no money spent and no human effort required.
Just a year before that study was published, the £1.5 billion upgrade of the A14 between Cambridge and Huntingdon was completed, with 850,000 trees planted as part of environmental enhancements that were meant to provide a biodiversity uplift of 11.5 per cent.
Over the course of the next year or so, somewhere between 50 and 70 per cent of those trees died and, despite two further replantings, the embankments of the new dual carriageway still appear today to be largely bare of anything living other than grass. Tens of thousands of plastic guards stand empty like corpses on a battlefield.
National Highways, which was responsible for the scheme, said the high failure rate (which it would not confirm to BBC Wildlife) was down to drought. It said that 90 per cent of 160,000 trees and shrubs subsequently planted survived and that it had met its “performance target of achieving no net loss of biodiversity in the period 2020-25”.
(It also declined to comment on whether it had achieved the 11.5 per cent biodiversity gain or not.) As of today, there is no reliable figure on how many trees, including those replanted, are still alive.
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Passive rewilding
The scientists who carried out the PLOS One study of what became known as the Old Wilderness concluded that “passive rewilding” such as this could make a “significant contribution” to the UK’s “ambitious woodland expansion targets at potentially no cost and within relatively short timescales”.
“Woodland has always been able to spread naturally, and it often does this by first being led by pioneer brambles and thorny shrubs like dog-rose and hawthorn,” says lead author Richard Broughton, an ecologist at the government-funded Centre for Ecology and Hydrology (CEH).
Brambles and other thorny shrubs protect saplings from damage done by rabbits and deer, whose gnawing can otherwise kill young trees.
“Tree-planting schemes rarely, if ever, include thorny shrubs like hawthorn, blackthorn or rose, let alone brambles, and so they don’t have this natural protection,” says Broughton.
Some grazing by roe deer can be a good thing, he adds, maintaining a few open areas where flowers and insects can flourish.
Why are tree planting schemes popular?
Given that the government is spending £400 million between 2024 and 2026 on tree planting (including peatland restoration), and given the remarkable failure rate on the A14 upgrade, all this begs the question – why bother?
Why not just let it happen naturally? The success rate will be higher and it doesn’t even cost a magic bean or two.
It all depends on the client’s and government’s objectives, says Niel Nicholson, finance director of the forestry consultancy Nicholsons. “If they want something to be established quickly, then you need to plant trees,” he says. “If they’re happy to wait, then natural regeneration will work fine.”
It also depends on what they want from their woodland. For timber and carbon sequestration, planting will work better. For wildlife, letting things grow naturally is the preferred option.
Broughton argues that the slow rate of natural regeneration is part of the point, providing scrub habitats that are excellent interim habitat for birds and insects.
Tree planting rarely has a 100 per cent success rate first time around, Nicholson points out. When his company planted 190,000 trees in 100ha of land owned by the Blenheim Estate in Oxfordshire, an estimated 40 per cent died in the first year.
“It was drought,” says Nicholson. “As soon as we finished planting in the winter of 2021-22, it was dry and, without any moisture, no tree will grow.”
You can’t water that many trees over that large an area, either, he adds, without hugely increasing costs to the client, and you’d need an abstraction licence, too.
The poor quality soil – Cotswold brash, which Nicholson says is 50 per cent stone – was another factor. He says after two replanting efforts (the second in a wet year), he is satisfied with the overall success rate.
Ensuring success
Yet some people argue that a 100 per cent success rate – or very close to – is possible if you follow certain rules. “Number one is managing herbivore pressure,” says Lewis Chisholm, woodland creation manager at the Forest of Avon Trust (FoAT), one of 15 community forest organisations in England.
That means either tree guards or deer fences or a combination of the two. FoAT also uses raptor posts to keep small mammals such as voles, whose gnawing can also damage young trees, on their toes.
Managing grass competition is also vital, adds Chisholm. “Grass competes with young trees for water and nutrients, and is more efficient at taking those up over the summer,” he says.
To combat this, the trust puts down biodegradable mulch mats with wood chips on top, which help to retain moisture as well as suppressing grass. Chisholm believes natural colonisation has a role to play in establishing woodlands, but that it’s not right for every site.
As well as the impact of herbivore pressure, he says that a naturally regenerated forest is likely to be less diverse. “You might end up with a woodland of two or three species, in contrast to one with 12 to 15 species, which you might have in a planted scheme.”
What are the downsides of natural regeneration?
A study published by scientists from Kew Gardens also found some drawbacks with natural regeneration. Because only about 10 per cent of England has woodland cover (the average for the UK as a whole is 14.5 per cent), woodlands that establish naturally are more likely to suffer from inbreeding.
“This is likely due to the lack of connectivity between forest patches, often isolated by large areas of farmland,” says Guillermo Friis, lead author of the research. When planting woodlands, Friis has recommended that seeds are chosen from a wider geographic area in order to maximise genetic diversity.
Niel Nicholson says achieving diversity when planting trees is vital – as is assessing which species will be likely to thrive in a changing climate. This includes some non-native species more likely to cope with hot, dry summers.
The Blenheim Estate project, for example, used 25 species, including a trial of foxglove trees, fast-growing, deciduous hardwoods native to east Asia. These died in the first drought. They also planted false acacia, a deciduous hardwood from North America. They thrived, despite the dry conditions.
Should the government be doing more to encourage natural regeneration? According to the Department for Environment, Food & Rural Affairs (Defra), in 2023-24, it supported 216ha of natural colonisation through its England Woodland Creation Offer, 6.4 per cent of the area planted that year.
It has also invested just over £1 million in “understanding the mechanics of natural colonisation and landowner attitudes”.
Clearly, there is a role for both ways of creating new woodlands. But is it absurd to suggest that natural colonisation is being, at the very least, undervalued, if not ignored – despite that recommendation made by Richard Broughton four years ago?
The government has an ambition of establishing 30,000ha of woodland in England every year – but in 2022-23, it achieved just 4,500ha and, on the face of it, natural regeneration’s 216ha the following year is negligible.
Groundbreaking studies, meanwhile, that make radical recommendations on how to do it better appear to be gathering dust.
