Leverhulme Wildfires Centre

Photo: Prescribed fires in the Cairngorms National Park, February 2023. Source: M. Valette

In this article, PhD student Michel Valette, from Imperial College London, reports on his findings from a research secondment with The Game & Wildlife Conservation Trust, in which he investigated future impacts of prescribed fires and woodland restoration in the Cairngorms National Park in the Scottish uplands. The secondment, funded by the Leverhulme Centre for Wildfires, Environment and Society, was conducted in collaboration with Dr Scott Newey from the Game & Wildlife Conservation Trust, and Prof. Kate Schreckenberg and Prof. Terry Dawson, from the Department of Geography at King’s College London. We thank the research participants for their time and contribution, and to all those who facilitated the research.

The full report, titled ‘Fires in the uplands: future impact of prescribed fires and woodland restoration on biodiversity and carbon stocks in the Cairngorms National Park,’ can be downloaded here, or accessed via Research Gate.

Future management of the uplands and the muirburn debate

From October to April, prescribed fires are lit across parts of the Scottish uplands to create mosaics of heather (Calluna vulgaris) patches of different ages, providing both high-quality feeding and nesting habitats to the red grouse Lagopus lagopus scotica ^1,2 and grazing corridors for livestock. Alongside predator and parasite controls, it allows grouse moor managers to produce a high enough density of red grouses for driven shooting (requiring a post-breeding density of at least 150 grouse/km²), a lucrative activity for sporting estates owning and managing large parts of the uplands ^3,4.

These prescribed fires, called muirburn in Scotland, are considered by some as an environmentally destructive practice benefiting only private estates and hunting interests, and by others as a necessary intervention to manage healthy ecosystems and provide jobs and income in remote communities in areas of otherwise low productivity ^3,4. Muirburn and associated management activities such as predator control and grazing management benefit certain vegetal and animal species, but negatively impact others and prevent woodland establishment ⁵. Muirburn reduces standing biomass and therefore the ‘fuel load’ available for further burning and could thereby prevent or reduce the occurrence and intensity of wildfires, but poor fire control during muirburn can also lead to escaped fires ^6,7.

Photo: Recently burned moorland to promote regeneration of old heather; Source: M. Valette

There is conflicting evidence about the impact of muirburn on peatlands and peat-forming vegetation, as well as long-term consequences on carbon sequestration and storage  ^5,7,8. About 40% of muirburn across the United Kingdom occurs on carbon-rich peatlands and frequently within protected areas, raising concerns about potential impacts on biodiversity and carbon emissions ⁹. In England, this has led to a licencing requirement, granted by DEFRA, for burning on deep peats (>40cm) located on sites of special scientific interest, special areas of conservation or special protected areas ¹⁰. Potential changes in the legislation are discussed in Scotland, such as restrictions of muirburns on deep peats and other sensitive areas or mandatory training.

Discussion about these restrictions and their economic impacts on sporting estates are part of a wider debate about the future management of the Scottish uplands and the ecosystem services they provide. Uplands management and ecosystem services provided will also be considerably influenced by woodland expansions effort. The Scottish Government has committed to increasing woodland cover from 18% to 21% of the Scottish land area by 2032 ¹¹, with open habitats identified as areas most likely to support new woodland cover ¹².

Woodlands expansion  is widely advocated as a means to tackle climate change, increase biodiversity, improve delivery of ecosystem services and increase ecosystem resilience ^13,14. However, indiscriminate woodland expansions can result in adverse side effects related to soil carbon storage, increased predation on neighbouring moorlands, social inclusions and displacement of traditional livelihoods ^15–17.

Photo: Moorlands managed with prescribed fires for red grouse driven shooting, Cairngorms National Park. Source: Google Earth

Muirburn and woodland expansion in the Cairngorms National Park

The Cairngorms National Park (CNP), covering 4,528km², is the largest national park in the UK and hosts 25% of its rare and endangered species. The CNP will be considerably impacted by both woodland expansion efforts and any future regulation of muirburn. Most of the land in the CNP is under private ownership and comprises 58% of heather moorlands with the majority managed through prescribed fires, and 17% of woodland.

The Cairngorms National Park Partnership Plan 2022-2027 ¹⁸ has set a target to achieve net-zero emissions for the region by 2045 through an ambitious programme that includes the expansion of woodland on 35,000 hectares (~8% of the CNP), and restoration of 38,000 hectares of degraded peatlands.

All land use and land management practices benefit and disadvantage some species, ecosystem services and associated stakeholder interests. The “identification and assessment of costs, benefits and risks and their distribution and trade-offs” could help to reach more equitable governance of protected areas and increase conservation effectiveness in the long term¹⁹.

In this study, we assessed the impact of land use scenarios for the CNP on the diversity of woodland types restored, habitat quality of five open-ground species and carbon storage. Based on the CNPA’s forest strategy and partnership plan ^18,20  and interviews with 9 stakeholders in February and March 20 23, we created 5 woodland expansion scenarios, differing in two aspects:

• Woodlands expansion strategy: limited expansion (17 500 hectares) on the most productive land, extensive expansion (35 000 hectares) on the most productive land or extensive expansion (35 000 hectares) on carbon-poor soils
• Prescribed fires: business-as-usual (from datasets described in Matthews et al. 2020) or restrictions on prescribed fires (~15% reduction of the areas managed by prescribed fires)

Figure: Map of the areas managed with muirburns and woodlands in the Cairngorms National Park. Areas in blue represent areas currently burned where the use of prescribed fires could be restricted, while areas in red are currently burned and would not be affected by prescribed fire restrictions.

We used the Native Woodlands Model, predicting the native woodland types likely to naturally regenerate across Scotland, to estimate the extent and diversity of woodland types that would likely be established/restored within the CNP ²¹. We used the habitat quality model of INVEST to assess impacts of land cover change on five important moorlands species in the park: red grouse, curlew (Numenius arguata), mountain hare (Lepus timidus), meadow pipit (Anthus pratensus) and black grouse (Lyurus tetrix); as well as the carbon storage model of INVEST to evaluate carbon sequestration after 40 and 100 years. The habitat quality and carbon storage models were calibrated using the best evidence available in the literature (see full report for more details on the methodology).

Future impacts on biodiversity and carbon stock

The proportions of different types of woodlands regenerated changed considerably according to the woodlands expansion strategy: expansion on the most productive land resulted in more upland oak-birch and Scots pine woodlands, while expansion on carbon-poor soils led to regeneration of more scrublands, junipers and birch/willows, vegetation types prioritized in the Cairngorms National Park Authority Forest Strategy ²⁰.

Photo: Landscape with regenerating riverine woodland, and moorlands managed through muirburn in the Cairngorms National Park. Source: M. Valette

Restrictions on the use of prescribed fires negatively impacted the habitat quality for red grouse, curlew and mountain hare, had a positive effect on the meadow pipit and no identifiable effect on black grouse. The woodland expansion strategy also has an important impact by increasing predation pressures from predators using woodland cover and woodland edge habitats. The black grouse benefited from woodlands expansion on carbon-poor soils, as it increases greatly the areas of forest adjacent to large patches of moorlands.

Woodland expansion on the most productive land is associated with important losses of soil carbon, that will not be compensated by biomass accumulation after 40 years. In the long term, it could sequester ~24% more carbon than woodlands expansion on carbon-poor soils. However, woodland expansion on carbon-poor soils is not associated with large losses of soil carbon during the first decades after planting/natural regeneration and is predicted to be carbon-positive after 40 years. Restrictions on prescribed fires have only a minimal impact on the carbon sequestration in biomass, while the potential impacts on soil carbon were not represented in the model as there is conflicting scientific evidence.

All the scenarios explored yielded different trade-offs between the diversity of native woodland types restored, habitat quality for open-ground species, risks of soil carbon loss in the mid-term, and sequestration of carbon in the long term. While woodland expansion on productive soils results in higher carbon sequestration and lower declines in habitat for some open-ground species, it induces a decreased habitat quality of black grouse, important loss of carbon in the soils after forty years and expansion of less scrub habitat, juniper and other less common vegetation communities.

Implications for the management of the uplands

The expansion of woodlands on carbon-poor soils presents some benefits for the conservation of the Scottish upland’s biodiversity and a lower-risk pathway to capture carbon, but it is likely to be the least favourable scenario for private landholders. Woodland expansion on carbon-poor soils, often located on steeper and more remote parts of the uplands, increase the cost and logistic of management measure associated with woodland management such as fencing, tree planting and deer stalking, while the lower biomass sequestration potential could result in smaller payment on carbon market.

The difference in the outcomes of scenarios sharing a similar woodland expansion objective of 35,000 hectares, highlights the importance of the location of woodland expansion efforts and complementary landscape management interventions, such as the use of prescribed fires, on future ecosystem services provided by the uplands.

The results show that restrictions on prescribed fire use will have a mixed impact on open-ground species, with a general decline in habitat quality for red grouse, curlew and mountain hare, and habitat improvement for meadow pipit, as well as a negligible impact on sequestration of carbon in biomass. The impact of prescribed fire restrictions is concentrated in parts of the park dominated by carbon-rich soils and will have a stronger economic impact on sporting estates in these areas, especially if they are unsuitable for mechanical mowing.

There are still two critical aspects regarding the role of prescribed fires in the carbon sequestration in the uplands that need further investigation. First, the impact of prescribed fires on the production and storage of charcoal in the soils, which could lead to secure long-term storage of carbon. Second, the role of prescribed fires in reducing the risks of severe wildfires, which is especially important in a landscape with significant woodland expansion efforts, an increasingly fire-prone climate and many visitors over summer.

References

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