Report Number 550 Review of the impacts of heather and grassland burning in the uplands on soils, hydrology and biodiversity English Nature Research Reports working today for nature tomorrow English Nature Research Reports Number 550 Review of the impacts of heather and grassland burning in the uplands on soils, hydrology and biodiversity Dr Graham Tucker BSc, MSc, PhD, MIEEM 5 Rosenthal Terrace, Hemingford Grey, Huntingdon, PE28 9BL Tel. +44 (0)1480 498395 E-mail [email protected] www.ecological -solutions.co.uk You may reproduce as many additional copies of this report as you like, provided such copies stipulate that copyright remains with English Nature, Northminster House, Peterborough PE1 1UA ISSN 0967-876X © Copyright English Nature 2003 Summary The aim of this study has been to summarise scientific information on the impacts of heather and grassland burning in the English uplands on biodiversity, soils and hydrology. Upland habitats are extensive in England and include a variety of habitats and associated species of conservation concern. This review has therefore given special attention to impacts on such habitats and their associated species. A detailed literature search and review has been carried out, supplemented with consultations with scientific organisations that have conducted research into upland burning. Most of the research on managed burning in Britain has been carried out on Scottish grouse moors, in particular studies on moorland burning histories, fire characteristics and impacts on Calluna vulgaris (heather) and heathland communities. Many of these research studies date back to the 1960’s and 70’s. Relatively few scientific studies have been carried out of the impacts of managed fires in England, especially on habitats other than dwarf shrub heaths. From current research evidence it is apparent that fire has long been a natural component of heathland and other upland ecosystems in Britain. As a result fire-influenced plant communities have developed, which are dominated by those species of plant that have adaptations that enable them to survive fires or rapidly regenerate afterwards. Humans have also used fires since Mesolithic times to clear woody vegetation and manage upland habitats for livestock, and this has been instrumental in the expansion of heathlands, mires and other open upland habitats. Since the early 19th century many heather moorlands have also been burnt for grouse management. Burning remains a common practice in much of upland England for agricultural and grouse management purposes. The principal aims of burning are to prevent establishment of woody species, to reduce litter and release nutrients, which stimulates earlier growth and temporarily increases the accessibility, palatability, and nutrient content of forage for grouse and livestock. Agricultural burns are usually uncontrolled and therefore tend to cover very large areas in one burn, typically from tens to hundreds of hectares. Grassland burning rotations are often very short, with fires typically returning every couple of years or annually in some areas. Burning on grouse moors is usually more planned and controlled, and carried out by burning strips of only about 30 m width and typically about 0.5 ha in total area, but larger fires are not uncommon. The normal aim on heather moorland is to burn when most Calluna reaches a height of 20 – 30 cm. This should typically result in a fire return period of about 10 – 15 years, in which case 1/10th to 1/15th of the land would be burnt on average each year. Data on the actual fire frequencies achieved on grouse moors in England are generally lacking, although it appears that there has been a decline in the practice of rotational burning in recent decades on the North York M oors. This situation may not, however, be typical as there is widespread concern in English Nature, based on observations by field staff, that burning management has intensified on some grouse moors, including the frequency of burning rotations. Burning is legally controlled in England and Wales by the Heather and Grass etc (Burning) Regulations and can only be carried out between the 1st October and 15th April in the uplands. In practice most burning is carried out in the spring due to the requirements for suitable weather conditions. It is evident from this, and other reviews that, in appropriate areas and circumstances, carefully managed burning can play an important role in the maintenance of some open semi- natural upland habitats in England. Carefully controlled prescribed management burns in appropriate habitats and conditions can arrest succession processes and maintain habitats of high conservation importance such as dry dwarf shrub heathlands. Fires may also help to maintain low nutrient conditions, which is an important characteristic of many upland habitats of high conservation value. And this process may be particularly important under current circumstances where atmospheric pollution results in nutrient inputs from rainfall that are higher than former natural levels. Burning of small patchworks of Calluna can also increase vegetation structural diversity and species-richness in plants, invertebrates and birds of Calluna dominated heathland habitats (although probably not on peatlands as these habitats have higher inherent levels of diversity). Regular burning also reduces fuel loads and thus to some extent the risks of large and very hot wildfires. However, the impacts of fires on soils, hydrology and biodiversity are complex and vary according to a number of interrelated factors. Characteristics of the fires are especially important, such as their frequency, temperature, ground surface intensity, residency time and size. These characteristics in turn depend on a range of factors including: fuel type and structure, width of fire, slope, wind and moisture levels in the vegetation and soil, and burning method. Impacts also depend on soil and habitat conditions at the time of burning (which partly reflect the cumulative impacts of burning), season, weather conditions and interactions with grazing and other management practices. Fires can have significant detrimental impacts, including: S Ignition, combustion and loss of peat and humus layers by hot fires in dry conditions. S Increased rates of run-off and erosion, particularly after hot fires and where large or old stands of Calluna are burnt, and on steep slopes. S Reduction in peat accumulation, even under well controlled prescribed burns, and potentially emission of carbon dioxide and other greenhouse gases from carbon stores in peat if these ignite or dry out as a result of hot burns. S Reduction of structural and species diversity and vegetation composition changes if carried out too frequently or over large areas. In particular, frequent burning dehabilitates Calluna and this has probably contributed significantly (together with high grazing pressures) to the loss of Calluna cover and replacement by grasses such as Molinia caerula (purple moor-grass) over much of the uplands. Burning also exacerbate severely overgrazed habitats if grazing animals are not controlled. S Post-fire establishment of invasive species such as Pteridium aquilinum (bracken), for example where old Calluna stands are burnt. S Destruction and long-term exclusion of fire sensitive and slow colonising species. S Removal of cover for ground-nesting wildlife and destruction of birds nests and clutches during spring burning periods. Furthermore, wildfires sometimes develop from poorly set prescribed management fires (eg in strong winds or where there is inadequate labour). These can be extremely severe, especially when they occur during dry weather (which is the most likely time). They can extend over very large areas and may also result in combustion of peat leading to soil degradation, severe erosion and long-term ecological and hydrological impacts. 6 Burning impacts vary considerably according to local circumstances. It is therefore difficult to provide generic recommendations for burning practices for soil and hydrological protection and nature conservation purposes. However, key general recommendations are to: S Produce burning plans for all areas subject to burning management (for whatever purpose). These should take particular account of impacts on soils and hydrology and the needs of Notified Features of interest within SSSIs and other statutory designated sites. S Take special efforts to minimise the risk of wildfires, particularly in areas of high biodiversity importance. As many wildfires develop from management fires, special attention should be given to identifying and taking the precautions that are necessary to avoid loss of control; this should form a key part of all burning plans. S Avoid burning peatland habitats, including wet heath and blanket bog, (unless there is a clear overall conservation benefit for doing so, such as the prevention of severe wildfires which may ignite peat layers in high risk areas) woodlands and scrub, bracken stands, montane habitats, screes and other rocky habitats and flushes. Areas that are used as traditional nest sites by protected species should also not be burnt whatever the habitat. S Generally avoid burning old stands of Calluna as these have low regeneration abilities and are prone to invasion by undesired species once burnt. They are also likely to produce hot fires which create further problems. Such stands should not be brought back into burning management unless there is a clear conservation reason