Protecting peat on moorland
There are many ways to store carbon in the uplands and to maximise soil water capacity to prevent flooding. Some are more or less compatible with the heather-dominated moors which the GWCT has shown provide refuges for some of our rarest breeding birds such as curlew. Recent research (Ward et al. 2013) shows that heather cover on peat soils is more favourable for carbon storage than grass cover. Other carbon stores in the uplands, such as planting trees, are obviously less compatible with open heather moors.
The rewetting of moorland (blocking up ditches and drains) is a proactive measure to stimulate more Sphagnum species growth and subsequently to increase the amount of carbon stored in deep peat soils. The GWCT recognises the potential value of rewetting areas of deep peat (>50cm) and restoring degraded bog habitat in storing carbon and biodiversity terms. We note, however, that evidence for the net benefits of this, balanced against the full rotation time for muirburn, cost and scale, are somewhat unproven.
Given the available science, the GWCT is unconvinced that a cessation of burning is a necessary component part of such a move. While there are concerns about burning on active peat bogs (EMBER 2014), there remains much contradictory evidence about the actual positive or negative impact of burning when longer timescales are taken into account.
We remain most keen to see enhanced carbon storage potential from wider upland habitats whilst simultaneously delivering wider ecosystem services, such as refuges for waders and black grouse, and jobs in remote rural areas. We illustrate this with two scenarios:
Scenario 1
No burn on blanket bog = carbon accumulation, possible changes in water quality and changes in biodiversity structure but actual levels and results of any of these not consistently proven. Declining sporting value with fewer rural socio-economic benefits and increasing risk to rare moorland species, which depend on moorland management, at the same time increasing wildfire risk.
Scenario 2
Burn blanket bog on 20-25 year rotation = 5 years of restricted carbon sequestration then 15-20 years of Carbon accumulation plus probable biodiversity benefits (lichen, bug and bird diversity) and likely retention of socio-economic ecosystem services from farming and grouse sporting income.
The GWCT supports moves towards longer burning rotations on blanket bogs in order to preserve the maximum possible ecosystem service from these areas.
If a change to longer burning rotations is needed to achieve our preferred approach of Scenario 2, getting acceptance of this may be more easily achieved using an approach that is targeted on willing participants, either single or groups of owners, supported with advice and well-funded remedial activity.
GWCT studies
The GWCT supported Durham University to produce three pieces of work on the effects of muirburn on upland carbon regimes that have influenced our thinking:
Does prescribed burning on peat soils influence DOC concentrations in soil and runoff waters? Results from a 10-year chronosequence.
- Given the large carbon store in these peatlands, concern has been raised over land management and its effect on the carbon dynamics of peat ecosystems.
- DOC is the name given to tiny pieces of carbon, derived from the natural breakdown of vegetation that are very fine and therefore difficult to filter out of water. It is what makes water a brownish tea colour.
- The study showed that prescribed burning by gamekeepers had no significant effect on DOC concentrations in soil water or surface run-off water in the years following burning. In other words, burning did not greatly intensify the “colour”.
Carbon stocks and carbon fluxes from a 10-year prescribed burning chronosequence on a UK blanket peat.
- This study showed that burning was a significant factor in determining the measured CO2 readings but that other factors such as month of sampling explained a greater proportion of the variation in the data.
- In other words, changes in levels of carbon went up or down greatly whether you burned or not.
- Even accounting for the loss of carbon during a burn itself, burning management shows an “avoided loss” of approximately 40 gC m-2 yr-1 carbon relative to no burning.
- Over the ten years, it is clear that burn management represents a technique for avoiding losses of carbon in heather-dominated peatlands.
Can prescribed burns contribute to carbon storage in peat soils?
- The study shows that although prescribed burning of moorland dominated by heather represents a direct loss of carbon to the atmosphere during the burn itself and by the destruction of litter production after the burn, this loss of carbon is outweighed by the production of both dead biomass and refractory black carbon (char) during the burn.
- Sites such as traditional grouse moors where burning has been practiced continuously for over 75 years represent greater average annual sinks of carbon than unburnt sites at all burn frequencies of five years or more.
- The study shows that significant carbon savings could be achieved by changing the burn frequency on areas already under burn management and extending it to be as close as possible to the maximum steady-state biomass for the site.
GWCT core site monitoring 2012-present
- Trust researchers have been recording peat depth and burning intensity on all our core grouse count sites where we already record numbers of passerines, waders and mountain hare.
- The aim is to establish whether grouse managers need to burn on blanket peat to retain a driven grouse interest.
- Interim results suggest that the number of fires keepers choose to have is correlated with peat depth, being less on deep peat sites and that burning rotations on heath of 12 years and bogs of 25 years support good levels of grouse breeding success.
Other relevant research
- Upland Evidence Review: Natural England recently conducted a thorough evidence review of direct relevance to these issues. The synthesis of this work can be found here.
Adam Smith and Gemma Davis
October 2014