Using bracken maps as a guide for regenerating rainforest

Image: An oak tree sprouts from a stand of bracken. Piles Copse, Dartmoor

Britain, we are told, has a ‘bracken problem’.

Hill-farmers hate it when bracken invades an upland pasture, it quickly overwhelms it, replacing grazing fodder with a plant that’s unpalatable (and indeed poisonous) to most livestock. Conservationists are wary of it: bracken invasion can quickly transform biodiverse heath, moor or grassland into a monoculture.

The most recent analysis estimates bracken now covers some 1.6% of Britain – which may not sound like much, but we should remember that buildings in the UK only cover around 1.4% of the total land surface. There are fears that a combination of reduced livestock grazing and climate change may mean bracken ‘invades’ still more of our upland areas in future.

But if you detect a hint of scepticism in my tone, you’d be right. I think that Britain’s bracken ‘problem’ is in fact an opportunity. I think it may be telling us something important about how we use our land, and how we should be sparing more of it for nature. In fact, some think that bracken – far from being a harbinger of doom – could provide a good guide for where we let native woodland return.

The ecologist Ian Rotherham has pioneered the study of what he calls ‘ghost woods’ or ‘shadow woods’. These are areas of land where woodland once existed, but where deforestation or overgrazing has led to its disappearance. Old woods, however, don’t entirely vanish even with the passing of trees – they often leave a signature in the soil. Seedbanks of woodland plants can still persist long after the woods have gone. That’s why it’s sometimes possible to restore ancient woodlands cleared for conifer plantations – once the conifers are removed, the ancient seedbanks lying in wait spring back into life. There are various plants that Rotherham and other ecologists consider to be indicators of lost woods – such as wood sorrel, bluebells, and bracken.

Bracken extends far beyond the edge of Black Tor Beare, one of Dartmoor’s three surviving upland oakwoods. Did the wood itself also once cover a much larger area?

Others are less sure that the presence of bracken denotes a former woodland, but still think that they indicate deeper, richer soils which are more suitable for trees in future. As an old hill farm saying goes, ‘Where there’s bracken there’s gold; where there’s gorse there’s silver; where there’s heather there’s poverty’. Indeed, the rich leaf-litter compost generated by bracken when it dies back in winter has been touted as a climate-friendly alternative to peat. In other words, bracken offers a potential guide for where to put ‘the right tree in the right place’.

Either way, the conclusion is the same: if you want to solve the ‘bracken problem’, then let the bracken stands revert to woodland. Ideally, to maximise species diversity and create a healthy age structure, this would be done through allowing the natural regeneration of trees and scrub. But where bracken has become such a dense monoculture that it shades out young saplings, there is a case for planting more mature tree standards and then letting the trees shade out the bracken (as a recent study centred on Dartmoor has also suggested). As those trees re-establish themselves, they can become the mother trees for a generation of naturally re-seeded saplings, aided by jays and squirrels attracted by the developing succession woodland / wood-pasture. As one authority on bracken says: “The planting of new woodland on land currently dominated by bracken is a long-term solution for control”.

Given bracken’s potential to guide reforestation efforts, I was delighted to be sent recently some new, draft datasets showing detailed maps of bracken in two of our upland national parks: Dartmoor and the Lake District. These two national parks also happen to be within Britain’s temperate rainforest ‘zone’ – where the oceanic climate makes it wet and mild enough for temperate rainforest, with its signature epiphytic mosses, lichens and ferns, to thrive.

Analysing the maps, I’ve found that some 35,000 acres of the Lake District is covered by bracken. With the total area of the National Park being 583,761 acres, that means bracken covers at least 6% of the Lake District National Park (with a true figure that may be even higher once the maps are finalised). Woodland cover in the Lakes is currently 13%, so allowing woodland regeneration just on bracken covered areas would take the total to 19%, smashing the NPA’s target to reach 17% woodland cover by 2050.

A coincidentally similar proportion of Dartmoor is also covered by bracken: some 14,370 acres, out of a total NP area of 236,170 acres – meaning that Dartmoor National Park is also 6% bracken cover. Dartmoor NPA has a commitment in its current Management Plan to “facilitate and fund the establishment of 2,000 ha [c.5,000 acres] of new valley native broadleaf woodland” by 2026: so, planting or allowing natural regeneration on areas of bracken would more than deliver this.

Data attribution: Habitat classification by University of Exeter SWEEP, for Dartmoor National Park Authority, 2021.

Some farming unions oppose large-scale reforestation in Britain on the grounds that it might dent food production. But the truth is, the vast areas of land covered by bracken – 50,000 acres in total across the Lakes and Dartmoor, far more across Britain as a whole – are not productive farmland. Some conservationists are also wary of woodland creation, lest it leads to ‘the wrong tree in the wrong place’ – such as trees planted on peat (a climate disaster) or on species-rich grassland (a biodiversity calamity). But encouraging trees to grow on bracken monoculture carries far lower risks.

What’s more, many of these vast bracken stands are sitting right next to our best remnants of old-growth temperate rainforest. I’ve pulled out a few examples in the maps below. Wistman’s Wood, Black Tor Beare and Piles Copse on Dartmoor – the three relict fragments of Atlantic oakwood on the moor – are all ringed by bracken (extensively, in the case of Piles Copse). The Borrowdale Woods in the wet heart of the Lake District have an even bigger bracken halo. Why not simply let these temperate rainforests expand into the surrounding bracken stands?

Data attribution: Bracken – Habitat classification by University of Exeter SWEEP, for Dartmoor National Park Authority, 2021. Woods – Ancient Woodland Inventory (England), published by Natural England under the Open Government Licence (OGL).

And thinking bigger, why not reconnect the Atlantic oakwoods of the Bovey river with their counterparts along the Dart – by transforming the ‘bracken belt’ on Dartmoor’s eastern flank into a ‘rainforest belt’ of regenerating trees and scrub (see image below). By reconnecting these currently isolated rainforest fragments, it would enable disjunct populations of rare lichens and bryophytes to more easily spread, allowing their spores and soredia to travel from branch to branch. It would create a wildlife corridor, too, for other species that make their homes in our temperate rainforests, like the pied flycatcher (whose populations have been in decline over the past 25 years).

So, rather than seeing bracken as a problem, maybe we should see it as pointing the way to a solution. Under bracken, there’s rainforest.

Thanks to Lee Schofield, RSPB site manager at Wild Haweswater, for putting me onto this subject; to Richard Knott, ecologist at Dartmoor National Park Authority; and to the University of Exeter SWEEP project.

10 thoughts on “Using bracken maps as a guide for regenerating rainforest

  1. This is an excellent proposal. The partial reforesting of Dartmoor needs to start in the obvious places: along the river valleys where there’s already well established deciduous woodland: Black Tor, Piles, Wistmans and parts of the Bovey and Dart valleys being the most obvious and most valuable. Much of this could happen through natural regeneration, but only if the target areas are properly fenced off so grazing ca be excluded or carefully conrolled.

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  2. Yes. I’ve been saying this for years!

    Aid the regeneration by sending in pigs/wild boar to the areas, where you can. They will stir up the seed bed and eat some of the bracken roots.

    Our ancient woods have been missing their full panoply of fauna.

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  3. I’ve been working in the Lake District as a forester for over 25 years. If only it were so simple!! I completely agree with the principle of planting up bracken-covered land. I wouldn’t want to be seen to be pessimistic but there are considerable barriers to accomplishing this good idea. Some of this land is common and planting on common land is a complex issue. We have far too many deer to avoid use of tree shelters or fencing which also come with their problems. In addition, the bracken will need treatment – most effectively with asulox which might not be popular! anyway juts a few thoughts….

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    1. Thanks Edward – I wouldn’t want to pretend it’s simple! The issues around commons are as you rightly say very complex – something I’ve explored a bit in other writing about Dartmoor, e.g. https://whoownsengland.org/2021/03/22/who-owns-dartmoor/. You’re quite right also that deer numbers are too high and without natural predators require culling and tree guards. Not so convinced about asulox though – what about increasing the natural process of trampling by livestock to break up bracken stands instead: sheep aren’t heavy enough (and have too much of a taste for saplings), but what about pigs or better still, wild boar?

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    2. There are complexities, as you suggest, but all of them can be overcome given enough time and effort- perhaps not everywhere but certainly on a lot of this land. I very much disagree about needing to use a herbicide: on the higher/harder ground where bracken growth isn’t so strong, it isn’t necessary to control bracken. Where bracken growth is stronger, then there are plenty of other techniques. We may need to accept a lower tree success rate and therefore have lower density woodlands than you might plant if your main objective is growing high quality, straight timber trees, but this would be a good thing from the biodiversity point of view as a lot of birds and insects love the open space within woodlands.

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    3. Stump up for Trees has planted on Bryn Arw Common with the consent of the commoners and permission from the Welsh Government to erect fencing, so it can be done.

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  4. I am a chartered town planner by profession with an interest in development plans for National Parks. This approach to identifying the right land in the right place for forestry land use is very welcome and long overdue. It has also been used in Canada since the 1970s. I agree entirely; bracken land is good for growing trees and has no value for agriculture. We should now move forward to support afforestation on bracken land, by discontinuing all agricultural grants for such land and adopting specific grants for such land for change of use to managed woodland. I do mean managed, but not micro-managed. I have grown trees on bracken land on my experimental woodland and I believe that doing nothing and calling it re-wilding, as some advocates for Dartmoor do, will be much too slow for any meaningful response to a climate change emergency; native trees do not naturally colonise bracken land easily. I grow a mixture of about 90 tree species on only 5 acres, so they are not all “only native species”, but that does not matter. The important fact is that my planted trees are growing very fast so my rate of carbon sequestration is about 10 times that of unaided re-wilding. With bracken land it is possible to grow only deciduous species with a significant native species content and also grow good quality commercial timber, so my site is also a Somerset Wildlife Nature Reserve, created on abandoned former agricultural land. It is therefore important to allow space for inovation by landowners, award grants on merit; and not by the dogma of only native species, or lists of specified species.

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  5. Trees grown far better in the soils below bracken than they do on sheep-grazed open uplands. And commons can be planted if stakeholders all agree – Stump up for Trees has done just that on Bryn Arw Common in the Black Mountains, S. Wales.

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