Non technical summary:
UK peatlands represent large stores of carbon (C), see Bellamy et al. (2005) and Garnett et al. (1998). During photosynthesis, plants take up carbon dioxide (CO2) some of which is subsequently respired back to the atmosphere, some of it quickly through plant respiration from shoots and roots. The remaining C is converted into organic matter which, after plants or their parts die, decays over time releasing the C back into the atmosphere as either CO2 or methane (CH4). Crucially, water logged conditions and some plant specific compounds (e.g. from Sphagnum mosses) suppress this decay or decomposition leading to ‘active’ peat formation as C inputs exceed C losses (Clymo, 1984). In the UK this has been the case over many millennia, contributing to a net cooling effect on the global climate due to reducing atmospheric greenhouse gas (GHG) concentrations (see Natural England, 2010).
However, the balance of CO2 versus CH4 emissions is important as CH4 is a GHG with a ‘global warming potential’ about 25 times higher (over 100 years) than CO2. Whereas decomposition above the water table mostly produces CO2, saturated conditions result in CH4 emissions (e.g. Heinemeyer et al., 2010). UK peatlands also provide other ecosystem services (ES) (e.g. Anderson et al., 2009) such as clean drinking water provision to millions of people (annually estimated to be worth about £1 billion or more), income to upland communities but also recreational activities to all of society.
In the UK, many blanket bogs having been drained for grazing, often combined with regular burning, which frequently leads to increased dominance of heather (Calluna vulgaris). However, heather dominance tends to dry the peat further as well as potentially causing underground erosion (‘peat pipes’) and suppressing ‘active’ peat forming plants such as Sphagnum spp. mosses (Lindsay, 2010). Whilst the drains (called grips) can be blocked to raise the water table and help restore 'active' peat accumulation, there is still a widespread need to investigate the dominance of heather which might impede this process. However, there is no clear evidence for only some species to be classified as "peat-forming" species; it is primarily the conditions (water logged and low pH) which lead to peat formation - although Sphagnum moss can create and/or support such conditions under otherwise unsuitable conditions. Higher water tables also tend to benefit bird populations feeding on soil animals (e.g. craneflies; see Carroll et al., 2011) that rely on wet peatlands.
However, certain heather management strategies currently in use (e.g. burning) may have detrimental effects on, for example, peat C stocks, air quality or water quality (see Worrall et al., 2006) and there is growing interest in finding alternatives. Moreover, management strategies depend also on accessibility, suitability, feasibility and peatland condition. Therefore, management and restoration schemes should consider these and other environmental consequences, which are linked to fundamental ecosystem services. Recent studies by Defra (and elsewhere) have highlighted these issues (e.g. Clutterbuck & Yallop, 2010; Critchley et al., in prep).
Importantly, the consequences of changes in management practice on biodiversity, carbon dynamics and water quality are likely to be slow to emerge so that long-term monitoring is needed. A combination of field and modelling work will identify those management or restoration options of greatest cost-benefit to restoring ‘active’ peatland and the associated ecosystem services.
Aims and Objectives:
The overarching aim of this study is to acquire experimental data to inform the recommendation of possible management techniques, for example, applicable through Environmental Stewardship schemes, to address the dominance of heather (Calluna vulgaris) and facilitate the support of ‘active’ blanket bog vegetation (with "peat-forming" species, particularly Sphagnum spp.). This requires screening for the most suitable management techniques and then including these as part of a long-term manipulative experiment to provide scientifically sound data to inform policy advice and subsequently management decisions.
The project will address four main objectives:
- Review potential techniques to address heather dominance and help support appropriate ‘active’ Sphagnum supporting peatland vegetation on blanket bog and identify practical management options for experimental testing.
- Field test identified management options and evaluating effects on:
a) plant species composition, including bryophytes, to indicate likely impact on peat formation;
b) water table and peat fluvial and gaseous carbon fluxes.
- Provide a cost-benefit analysis to determine the cost of achieving a range of ecosystem services.
- Evaluate the impact of treatments on vegetation dynamics, stream flow, water budgets, carbon stocks, fluxes and greenhouse gas emission based on measurements and modelling approaches.
This project performed a literature review (Phase 1), and will perform a comprehensive set of long-term field experiments and, working toward a cost-benefit analysis (CBA), will investigate how different management measures affect vegetation composition and associated ecosystem services. The rigorously designed field experiments compare ‘control’ to 'treatment' areas, where large-scale mowing and other smaller nested treatments replace the usual burn regime at three sites, two in Yorkshire in collaboration with the Yorkshire Peat Partnership (YPP), Nidderdale and Mossdale, and another at the Forest of Bowland (United Utilities).
However, robust long-term trajectories (and thus benefits) of management changes can only be expected to be revealed in future years (Phase 2+; currently running until 2022), once vegetation re-growth and a full management rotation covering the entire catchment has been achieved. This applies particularly in relation to carbon budgets, net GHG emissions, hydrology, water quality and vegetation dynamics, all of which would be central to any comprehensive and meaningful CBA.
Required time periods for a continuation of monitoring towards providing such robust long-term policy relevant evidence on key ecosystem parameters (based on catchment rotational management, inter-annual climate variability and vegetation growth rates and plant community development) can be estimated to require between 10 to 25+ years depending on the parameter, e.g. for C budgets (10+ years), GHG emissions (15+ years), water budgets (20+ years) and vegetation dynamics and biodiversity (25+ years).
Below are shown the four stages of a conventional burn on a heather dominated grouse moor. The four short films were taken in 2015 (Nidderdale):
Clockwise from top left: Setting off for a burn with the Argocat and water tank filled up, starting the fire with a gas flame, the fire going strong and, finally, putting out the flames with the water from the tank. Quick and safe.