Key points
Background
Prescribed burning is a centuries-old tool, used across UK moorlands to maintain open landscapes. In the UK, prescribed burning on moorlands (known in Scotland as muirburn) is used to improve grazing and to manage moorland habitats in support of higher densities of red grouse beneficial for recreational shooting. For grouse management, burning typically involves burning small patches of heather on a rotational basis, creating a mosaic of different aged patches of vegetation. This mosaic provides food, shelter, and nesting habitat for grouse and can have biodiversity benefits such as supporting ground nesting birds, particularly upland waders.
The reduction in biomass, flammable material particularly tall, woody vegetation through prescribed burning means that it can be used to reduce the amount of
combustible material, or fuel load, in the landscape and thereby reduce the extent and the damage done by wildfires. Across the world, such as in Mediterranean shrubland and savanna ecosystems, prescribed burning is used as a tool for mitigating the risk of wildfire. Yet there is the possibility that prescribed burns can become out of control and be an ignition source for wildfires. This risk combined with increasingly hotter and dry conditions, negative media coverage, and concerns of the effects of prescribed burning on carbon stores and carbon sequestration has put the management tool under growing scrutiny. In England it has led to proposals to extend the area where controlled burning is prohibited.
Moorland habitats include temperate shrub-dominated heathlands, rough grasslands and peat bogs which have high biodiversity and cultural value. However, shifts in land use have led to reduced grazing and burning on moorland, raising concerns about higher fuel loads potentially leading to larger and more intense wildfires and greater damage to soils and the wider ecology of the moorland.
In Scotland there are compulsory codes of practice (Wildlife Management and Muirburn (Scotland) Act 2024) aimed at supporting a balanced approach to muirburning, these generally discourage intensive burning rotations on peat soils. In order to help address concerns that prescribed burns increase wildfire risk, this study aimed to assess whether wildfires occur less frequently in areas subjected to muirburn.
What they did
This study assessed the spatial co-occurrence of muirburn and wildfires across Scotland. Presence or absence of muirburn was assessed from high-resolution aerial imagery from 2018, covering 491 land holdings across 14,137 – one km2 National Grid squares. Muirburn intensity was calculated and allocated into six categories; 0% (no muirburn), and 1-20% up to 81-100% burnt area.
Data on wildfire incidence was collated from satellite and aerial detection sources covering the period 2015 to 2020. This included before and after the 2018 muirburn mapping year to account for older muirburns. Maps of estimated muirburn intensity were overlaid with maps of wildfire locations and dominant vegetation habitat types (acid grasslands, heather grasslands, heather heathlands, and peatbogs), and peat soil and peat depth taken from the UKCEH Land Cover Map.
Researchers analysed patterns of wildfire, muirburn, and land cover, using digital mapping and spatial analysis tools. By considering the type of land cover, peat depth and burn intensity, they calculated how much land was affected by both muirburn and wildfires.
What they found
Overall, 96 % of the total wildfire area occurred outside moorlands managed by muirburn, with wildfires covering 1.1% of total moorland area.
Only 0.4% of the total moorland area with evidence of muirburn also had records of wildfire occurrence (18km2 out of 5,066km2). The average size of wildfires in areas with evidence of muirburn was 1.54km2 versus 2.16km2 in areas without evidence of muirburn, however this difference wasn’t statistically significant
Outside of areas with evidence of muirburn, moorland wildfires were more prevalent especially within grasslands, peat bogs, and habitats on peat soils, with 75% of the total wildfire area occurring on peat. In contrast, muirburn was more common in heather heathlands on non-peat soils, with only 32% of the muirburn area on peat. Heather grassland stood out as the habitat with the highest number of wildfire incident records and the largest area affected in both areas with and without muirburn. Wildfires in acid grassland, heather heathland and peat bogs occurred more frequently than expected in areas that had not been subjected to muirburn.
However, in terms of total area, wildfires burnt 331km2 of peatland habitat, while muirburn was recorded on 1,628km2 of peatland habitat. This means that even though wildfires mostly occurred on peat muirburn affected a greater area of peatland overall.
Most of the moorland in this study showed either no evidence of muirburn or only low-intensity muirburn (> 20%), but heather heathland habitat experienced more high-intensity muirburn than other habitats. Wildfire prevalence was highest within the 1-20% muirburn intensity category, dropped within 21-40% category, and then increased again when muirburn intensity was greater than 41%. This pattern was mainly visible in heather heathland. For heather grassland, the highest occurrence of wildfires occurred at 41-60% muirburn intensity, and especially on peat soil.
Overall, the relationship between muirburn intensity and wildfire occurrence is complex, and varies with the type of habitat.
What does this mean?
This study suggests that wildfires are less frequent in areas where muirburn is carried out. One possible reason is that muirburn reduces the amount of vegetation (fuel) available, so it lowers the risk of a severe wildfire and provides fire & rescue services with opportunities to control the wildfire. Another possibility is that landowners that use muirburn also have other wildfire prevention measures in place, which could explain the lower prevalence of wildfire in these areas. It is also possible that these areas receive fewer public visitors, so there’s a lower chance of accidental fires started by people (e.g discarded cigarettes or campfires).
The greater occurrence of wildfire in heather grasslands at higher muirburn intensities may be due to pre-existing high fuel loads and the higher flammability of grasses at higher moisture contents. Similarly, the higher occurrence of wildfire on peat may be driven by degraded and drained peatlands and resulting low moisture levels, although more research is needed in this area.
The evidence that muirburn reduces wildfire risk remains complex and somewhat uncertain. This paper reports limited spatial overlap between muirburn and wildfire in Scotland, which could suggest fuel-load reduction is effective, but also could reflect better fire management or lower ignition pressure on estates that burn. However, it is important to note currently the practice of muirburn is not designed for wildfire mitigation and a more targeted prescribed burning technique could be applied.
Habitat type is also important: grassy systems are more fire-prone than heath or shrub habitats, so prescriptions must be tailored to vegetation. Licensing must be shaped by evidence and site context.
Muirburn requires careful regulation, with practitioners trained in safe methods. Licensing should remain accessible, but be underpinned by current best knowledge, to balance fire prevention, ecological health, and wildfire risk beyond managed areas.
Authors: Debbie Fielding, Scott Newey, Robin J. Pakeman, Dave Miller, Zisis Gagkas, Keith Matthews, Stuart W. Smith