Muirburn – no smoke without fire?

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A recent paper by Murgatroyd et al (2019), revealing the remarkable rate at which hen harriers disappear over grouse moors, has had even shooting industry stalwarts holding up their hands and admitting that the grouse shooting industry has a problem, even while some still try to pretend that the criminals represent a minority.

This devastating report will surely bring licensing a step closer, but of course raptor persecution isn’t the only problem with the grouse shooting industry, with related issues linked to wider economic impacts, social justice, water quality, flood risk and biodiversity, as well as the poorly monitored use of medicated grit and over zealous use of legal predator control on and around grouse moors.

But I wanted to look into the other burning question (sorry, I couldn’t resist): the role of muirburn (prescribed fires used to maintain moorland). Such fires are employed to to halt natural vegetational succession (which would otherwise typically see heather moorland revert to scrub and eventually woodland) and promote new heather growth, maintaining the environment in a condition especially favourable for grouse and grazing livestock.

Land managers like to tell us that muirburn is a good thing, while anti-grouse shooting campaigners frequently condemn it as disastrous and damaging, so which is it? Well, it’s a bit of both, as we shall see, and neither side seems keen on presenting the whole story, so I have tried to summarise what I have been able to find out.

Firstly, the good. Muirburn maintains moorland in a state that supports higher densities of several threatened bird species than occur elsewhere, including the Eurasian curlew (Newey et al. 2016) – one of the UK’s highest conservation priority bird species. Many of these upland bird species also benefit from legal predator control on such moorland, and while critics of this practice might prefer to let nature manage herself, even the RSPB has invested in trials of crow and fox control in desperate attempts to save the rapidly declining curlew. In the absence of apex predators able to control abundant mesopredators, conservationists have little other choice.

Shooting advocates also claim muirburn is intrinsic to maintaining the iconic heather clad hillsides widely praised for their beauty in July and August, while opponents point to the bleak, drab moorlands the rest of the year, scarred by fire and devoid of trees, and say: “What beauty?

As with every aspect of this issue, there are two sides to the story. Muirburn can be used to mitigate the risk posed by wildfires and has been endorsed by the Scottish Fire and Rescue Service. But an SNH commissioned review (Werritty et al. 2015) concluded that:

Whilst large, intense wildfires can be destructive, many may have no greater impact than prescribed burns (Clay et al. 2010) and evidence suggests that over 50% of wildfires with known causes may themselves be caused by loss of control of prescribed burns.

That’s right. Remarkably, the muirburn supposedly being used to prevent wildfires is itself the most common cause of those fires!

On the other hand, while many wildfires may have no greater impact than prescribed burns, some undoubtedly do and the worst wildfires can damage peat as well as peat-forming species, such that they can do significant damage (Davies et al 2015), leading to erosion losses of up to 1 metre of peat if bad fires (hotter than the light scorching of well-managed muirburn) are followed by heavy rainfall (Marrs et al 2018), and thus undoing any of the benefits to peat accumulation of a zero burn policy. That is why many people continue to advocate for prescribed burning – to mitigate this risk.

Of course, another way to mitigate the risk of wildfire would be to promote re-wetting of moorland, blocking up drainage ditches misguidedly cut in the past, and all sides agree that this would be a good thing, although one suspects that grouse moor managers may secretly be less enthusiastic about this process than conservationists, since grouse do not thrive on boggy ground, and government-funded schemes to promote such rewetting have sometimes yielded little obvious work from estates.

Prominent amongst the other common criticisms of muirburn is the fact that it allegedly contributes to climate change, releasing carbon into the atmosphere, drying out peat bogs and inhibiting peat formation. This is a non-trivial concern. Peat (formed when plant material fails to fully break down due to a lack of oxygen in waterlogged soils) is a major store of carbon, holding around 30% of the world’s soil carbon and representing the largest terrestrial carbon store in the UK.

In response to this particular criticism, the pro-shooting Gift of Grouse website cites studies that it says prove that muirburn at least does no harm, but predictably they tend to use scientific studies like a drunk uses a lamppost – more for support than illumination, and are notably selective in their review.

They start by citing Marrs et al (2018) who explored the carbon capture rate in experimentally burnt peatland in a long term study over 53 years. The study examined the impact of different burn frequencies (0 – 6 burns) and reported that contrary to widely held suspicions, carbon storage and peat generation did continue to occur regardless of burn frequency, albeit at a decreasing rate with increasing burns, with peat and carbon accumulation around 4% lower for each additional burn and accumulation significantly reduced in the most intensively burnt plot compared to the least. Furthermore, even the most intensive burn regime they studied amounted to only one burn every ten years. Most grouse moors are burned far more frequently than that.

And there are limits to what we can conclude from this study. It assumes we want to keep the land as moorland, and many people would prefer a more natural and heterogenous matrix of woodland and open areas. Rotationally burnt moorland may support more plant species than moorland that has been unburnt for half a century, but how does it compare to native woodland? 53 years isn’t long enough to allow succession to re-establish climax woodland, but if and when woodland did replace moorland it would almost certainly exhibit greater floral and overall biodiversity – and if it was interrupted by boggy patches of moorland it certainly would.

Of course, there are good arguments for preserving peatlands. They are a unique habitat and a vital store of carbon. Plantations of alien tree species have destroyed many of these habitats, in Ireland in particular, and done great damage. But it is not an either or situation. We could have both more native woodland and healthy peatlands.

Lastly Marrs et al (2018) only examined floral diversity, and although floral diversity is a common substitute for overall biodiversity, it is not a totally reliable guide. For example, insect diversity and abundance tends to increase with vegetation height. Thus older, taller heather might be expected to support a greater number of insects than a shorter, younger sward, perhaps even when that shorter sward supported a marginally greater number of plant species (the Moor House National Nature Reserve where Marrs et al conducted their study only supports small numbers of plant species, even in their most diverse plots).

The second study cited by Gift of Grouse provides even more tenuous support for muirburn. This time Heinemeyer et al (2018) used sediment cores to investigate carbon storage and peat formation in peatlands, noting that carbon was stored in all three of the analysed sites during periods of burning and that carbon storage was in this instance actually positively correlated with burn frequency, although what that burn frequency was is not stated, nor is any comparison made to unburned sites, making it difficult to draw “robust conclusions.”

Gift of Grouse finish by referencing studies on the main peat-forming species, sphagnum moss and cottongrass. Whitehead and Baines (2018) found that these two species were most common on moorland 3-10 years after a burn, declining thereafter as the heather fully re-established its dominance. Marrs et al. (2018) also showed that plant biodiversity was highest on the most regularly burned of their study plots (but remember, that was only one burn every ten years) and the least biodiversity was recorded on the plot burnt only once. They concluded that the most beneficial burning regime in their area would be one burn every 20 years, striking a balance between a regime that favours peat forming species and the reduced rate of peat formation and carbon storage associated with those burns.

With no personal expertise on this subject it is hard to know what to make of the issue and government reviews have often concluded with a call for more research. My feeling is that muirburn can be beneficial, if used appropriately, but importantly this likely depends on both the frequency and the scale of the burns. Muirburn for grouse shooting probably does not represent the optimum in this respect, likely taking place too often, on too large a scale and in the wrong places, contributing to wildfires as much as preventing them and damaging peatlands at least as much as helping to form them, as well as having been identified as a possible contributory factor in the long-term decline of breeding merlins on grouse moors in the Lammermuir Hills (Heavisides et al. 2017). The failure of estates to find this balance was recognised by the Cairngorms National Park Authority in 2017 when they observed:

“Good moorland management makes a significant contribution to delivering conservation priorities set out in the Partnership Plan. In some places, however, the intensity of management measures to maintain or increase grouse populations is out of balance with delivering wider public interest priorities.” 

Indeed, inappropriate burning is cited as one of the main reasons contributing
to the ‘unfavourable’ condition on 87% of ‘unfavourable’ upland bog features in Scotland (Scottish Natural Heritage 2010). It is also important to remember that alternatives to muirburn exist, including cutting the heather mechanically, although these may not be feasible everywhere and the process has its own drawbacks.

Muirburn is ostensibly guided by the muirburn code, a recently revised mixture of legal requirements and best practice recommendations, but enforcement action is rare and landowners regularly flout the rules. Despite the Muirburn Code advising against burning on deep peat, Douglas et al. (2015) found that 28% of all 1km squares subjected to burning in Scotland were located over deep peat, while the annual number of burns increased by 11% per annum between 2001-2011 as grouse moor management has intensified.

I believe grouse shooting’s ills can only be fixed by a ban. But I don’t know that for certain. For now, licensing seems like a fair compromise – a chance for estates to show they can operate ethically, within the law and without doing the damage they do at the moment. It seems to me that licensing for driven grouse shooting is also now inevitable, but when it comes it should include much stricter rules about when and how muirburn is carried out, with powerful sanctions available to punish those landowners who continue to feel they are above the law.

Increasingly, the world is watching.


 

Hugh Webster is a freelance conservationist and the author of The Blue Hare, a story about mountain hares set on a Scottish grouse moor.

References:

Davies, G. M., Gray, A., Rein, G. & Legg, C. J. (2015) Peat consumption and carbon loss due to smouldering wildfire in a temperate peatland. For. Ecol. Manage. 308, 169–177.

Douglas, J.T., Buchanan,G.M., Thompson, P., Amar, A., Fielding, D.A., Redpath, S.M. and Wilson, J.D. (2015). Vegetation burning for game management in the UK uplands is increasing and overlaps spatially with soil carbon and protected areas. Biological Conservation 191:243-250.

Heavisides, A., Barker, A. and Poxton, I. (2017). Population and breeding biology of merlins in the Lammermuir Hills. British Birds 110: 138-154.

Heinemeyer, A., Asena, Q., Burn, W. L. & Jones, A. L. (2018) Peatland carbon stocks and burn history: Blanket bog peat core evidence highlights charcoal impacts on peat physical properties and long-term carbon storage. Geo: Geography and Environment 5, e00063.

Marrs, R. H. et al. (2018) Experimental evidence for sustained carbon sequestration in fire-managed, peat moorlands. Nature Geoscience. doi:10.1038/s41561-018-0266-6

Murgatroyd et al. (2019) Patterns of satellite tagged hen harrier disappearances suggest widespread illegal killing on British grouse moors. Nature Communications vol 10, Article number: 1094 https://www.nature.com/articles/s41467-019-09044-w#Abs1

Newey S, Mustin K, Bryce R, Fielding D, Redpath S. (2016) Impact of Management on Avian Communities in the Scottish Highlands. PLoS One 2016; 11.

Scottish Natural Heritage (2010). Condition of Designated Sites. https://www.nature.scot/sites/default/files/2017-07/B686627%20-%201%20-%20
SCM%20%28Final%29%202010%20Full%20Report-lr%20-%205%20
August%202010.pdf

Werritty, A., Pakeman, R.J., Shedden, C., Smith, A., and Wilson, J.D. (2015). A Review of Sustainable Moorland Management. Report to the Scientific Advisory Committee of Scottish Natural Heritage. SNH, Battleby.

Whitehead, S. C. & Baines, D. (2018) Moorland vegetation responses following prescribed burning on blanket peat. Int. J. Wildland Fire 27, 658–664.

2 thoughts on “Muirburn – no smoke without fire?

  1. wildmattcross March 25, 2019 / 11:52 am

    I’ve never been called a stalwart before. I don’t know if that is a good thing or not. Better than other types of wart I suppose.

    Like

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