Burning and Cutting Both Promote Peat-Forming Species on Blanket Bog

✅ KEY TAKEAWAY: Both burning and cutting reduced heather dominance on blanket peat and promoted Sphagnum moss and cotton grass recovery within five years.

A five-year experiment across grouse moors in the Pennines has found that both prescribed burning and mechanical cutting of heather reduce its dominance on blanket peat and promote the growth of plant species associated with healthy, actively forming bog.

Sphagnum moss cover recovered fully within five years of management and exceeded pre-treatment levels, while cotton grass cover tripled. The study adds robust experimental evidence to one of the most contested debates in upland land management.

How the experiment worked

The research, published in Applied Vegetation Science by Sian Whitehead, Nicholas Aebischer and David Baines, used a before-after-control-impact (BACI) design - widely regarded as the gold standard for ecological field experiments. Eighty plots were established across five blanket bog sites in the North Pennines and Yorkshire Dales, each managed for red grouse. Four treatments were randomly assigned within each block:

• Prescribed burning

• Cutting with brash left in place

• Cutting with brash removed

• No management (control)

What happened to heather and peat-forming species

Pre-treatment heather cover averaged 76% across all plots. Burning reduced this by 97% and cutting by 87%. As heather dominance fell, other species took advantage of the increased light reaching the ground layer:

• Cotton grass (Eriophorum vaginatum) - a key peat-forming species and an important spring food for grouse - increased threefold, peaking in the third year after management before settling back as heather began to recover.

• Cross-leaved heath (Erica tetralix) cover increased fourfold relative to unmanaged plots.

• Bilberry (Vaccinium myrtillus) responded particularly well to burning.

Sphagnum moss, perhaps the single most important genus for peat formation, was initially reduced by management - most markedly by burning, which cut Sphagnum cover by around two-thirds in the first year. However, recovery was consistent across all five sites.

By the fifth year, Sphagnum cover in managed plots averaged 96% of that in unmanaged controls and was nearly a third higher than pre-management levels in the same plots. The number of Sphagnum species present showed no decline after burning, and there was a slight tendency for species richness to increase over time across all management types.

Burning versus cutting - and the brash question

The two cutting methods did produce some differences worth noting. Cutting reduced moss depth (the distance from the moss surface to the peat beneath) more than burning did in the first two years, supporting earlier findings that mechanical cutters can slice the tops from moss hummocks.

Leaving cut brash on the plots slowed Sphagnum recovery compared to plots where brash was cleared away, probably because the brash smothered regenerating moss. On the other hand, brash removal left more bare ground, at least initially.

From a wildfire perspective, the brash question matters. Wildfire ignition is most likely in the litter layer, and accumulated cut material adds directly to that layer. Prescribed burning, by contrast, removes fuel.

Given current regulations that heavily restrict burning on deep peat but generally permit cutting, the authors flag a concern that the shift towards cutting without brash removal could inadvertently raise the risk of wildfire - particularly as climate change brings drier summers to some peatlands.

What happened on unmanaged plots

The unmanaged control plots told their own story. These retained dense heather canopies with a ground layer dominated by pleurocarpous (feather) mosses - species that thrive in shade beneath tall shrubs but contribute less to active peat formation than Sphagnum.

In managed plots, these feather mosses declined, while acrocarpous (cushion) mosses - species that rapidly colonise open ground - increased sharply, particularly after burning, where their cover rose nearly three and a half times over five years.

How this fits the wider evidence

These findings are consistent with several other studies. The 60-year burning experiment at Hard Hill on the Moor House National Nature Reserve found that Sphagnum and cotton grass cover was greater under a ten-year burn rotation than where burning had not occurred for 90 years.

A separate ten-year government-commissioned study on three other northern English grouse moors reached similar conclusions. Taken together, the evidence increasingly suggests that negative impacts of management are short-lived, while the longer-term trajectory favours the peat-forming plant communities that conservationists wish to see.

Implications for policy and practice

The authors note that this trajectory needs to be considered more carefully in regulatory reviews. They point out that some Natural England evidence reviews have relied on short-term or space-for-time studies - approaches that capture the initial disturbance but may miss the subsequent recovery.

They also highlight what they describe as an inconsistency in the regulatory framework: prescribed burning on deep peat now requires exceptional circumstances to proceed, while cutting consent is typically granted despite limited evidence on its long-term effects and known concerns about damage to the peat surface.

Five years is still early in what may be a 15- to 25-year management cycle, and the researchers stress the need for continued long-term monitoring. But the direction of travel is clear.

Both burning and cutting shift blanket bog vegetation away from heather dominance and towards the Sphagnum-rich, cotton grass-rich plant communities associated with active peat formation and carbon storage.

For moorland managers weighing up their options, the choice between burning and cutting may come down to practical site conditions - but the ecological outcomes, at least within this timeframe, are broadly comparable.

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