Restoration of heather-dominated blanket bog vegetation on grouse moors for biodiversity, carbon storage, greenhouse gas emissions and water regulation: comparing burning to alternative mowing and uncut management

The overall long-term aim of project BD5104 ‘Restoration of blanket bog vegetation for biodiversity, carbon sequestration and water regulation‘ was to deliver robust and credible (long-term) experimental evidence to underpin the development and refinement of possible management techniques, to reduce the dominance of ling heather and support the development of ‘active’ blanket bog vegetation with a high cover of “peat-forming” species, particularly Sphagnum moss. The study included a one-year pre-management change period and was designed as a paired catchment study, at each site comparing burning to alternative mowing, with several additional plot-level treatments including brash removal, Sphagnum addition and an uncut (no management) comparison.

Over 25% of the UK land area is covered by uplands, a large proportion of which comprises blanket bog covered by heather moorland. Blanket bogs are peatlands where high water tables, together with acid conditions, suppress decomposition of dead organic matter. Long-term peat development, mainly since the end of the last glacial period, has resulted in extensive and fairly deep (2-4 m) peat cover. This peat accumulation represents a major UK carbon (C) stock which is linked to a range of key ecosystem services, particularly water storage, flood prevention, drinking water provision and biodiversity. In England, only few areas of blanket bog are classified as in a favourable condition as many bogs have been drained and suffered from past management. About 10% (about 1.2 million ha) of the UK upland area, and 30% of UK blanket bog, is managed for red grouse by rotational burning to encourage growth and dominant cover of their major food source, ling heather (Calluna vulgaris). Whilst grouse moors support local economies, their management (often with remaining drainage and ongoing heather burning) has been linked to negative impacts on water tables, C storage, water quality and biodiversity. However, there is little, and sometimes conflicting, evidence on the impacts of grouse moor management. Furthermore, climate change poses another challenge, as changes in rainfall patterns and rising temperatures are a potential threat to bog functioning.

The outcomes of the research highlighted four key aspects:

1) Management impacts need to consider pre-management differences, climatic and environmental events and site specific conditions. Overall, comparisons between the two types of management, particularly concerning C storage, C fluxes and GHG emissions, highlighted the need for continued management and monitoring over at least a complete management cycle (ca. 10-15 years). The study highlighted the value of long-term and holistic research within an applied, practitioner-relevant context for both evidence-based policy and scientific impact.

2) So far, burning appeared to be the least beneficial form of management intervention towards supporting ‘active’ bog vegetation, particularly at the driest site, although surface C accumulation was high due to charcoal impacts on C storage. However, no negative management impact on water quality was observed. The uncut option showed few, if any, downsides apart from limited recovery of a “peat-forming” bryophyte layer at the driest site. Mowing regardless of brash management seems to encourage key species and re-establishment of a ‘typical’ bog community, particularly at the wettest site.

3) Mowing raised peat moisture and water tables with benefits to cranefly abundance and thus bird populations under dry conditions but potential negative impacts on generally wet sites, of particular relevance for climate change impact scenarios. Mowing also showed reduced stream flow at two sites with important downstream flood alleviation impacts during intense short-term rainfall events. However, mowing also led to increased phosphorus stream flow export from brash decomposition with potential implications on reservoir eutrophication and encouraged sedge vegetation with likely negative impacts on water quality and methane emissions.

4) Net C flux budgets for uncut plots showed greatest C gains at the wettest site whilst the driest site was a small net C source. Both management options switched from a net C sink to a similar net source after management. Although ‘active’ blanket bogs are a long-term C sink, they have the potential to emit large amounts of methane from anaerobic decomposition, particularly under warmer and wetter conditions, potentially causing a net positive contribution to greenhouse gas (GHG) emissions and overall global warming. Management needs to consider the interaction between climate, hydrology and C fluxes.