The Problem of Muirburn
The aftermath of any heath, moor or grass fire looks ghastly, and even if the location affected recovers, visibly, quite quickly, (sometimes within just a few months), there can be no doubt that environmental damage has been done. Sometimes, of course, that damage is considerable. In this paper, I want to focus, at least initially, on heather-burning, the ‘muirburn’ of the Highlands and Islands, where the topic is often and understandably controversial.
The practice of muirburn across the Highlands is often contrasted: roughly, east versus west. In the east, the practice is seen at its most ‘organised’ , a pattern of small, close, repeated burns which is carried out as part, often, of the management of an intensive grouse moor. It is entirely true that this type of muirburn is often well-controlled, that it produces well-flowering heather, and helps to maintain an unnaturally large population of red grouse.
Repeated over a long period, there is little doubt that it significantly reduces the number of plant species, (and, therefore, the overall biodiversity) on such moors. Some 20 years ago, I was working on the moors of Northeast Perthshire and Angus; the heather was blooming beautifully, but I could find remarkably few other plants. The area was becoming a monoculture of heather. This in itself represents an overall reduction of biodiversity, and could be very vulnerable to some new pest or disease. And the burning, while regenerating heather, very effectively kills pine and juniper which would otherwise colonise these drier moors, and probably grow well.
During the same period, I also noticed that while, from a distance, this might look like exemplary heather management, there was also some poor practice: areas of very shallow peat or peaty soil around rocky outcrops had been burnt as much as any other place. Here, the charred peat was crumbling; we knew even then that this encourages erosion of what little ‘soil’ there actually is, but we now know that the charred peat will be releasing carbon dioxide and methane to the atmosphere. (And it struck me that these rocky outcrops or ‘cairns’ might be being burnt to dissuade any potential predators like wildcat or pine marten from using them as dens).
In places, too, I saw the soft heather shoots from a previous burn being consumed by uncontrolled grazing; on a few occasions, some concentrations of hill sheep, on a few others by no less than three species of deer; once all on one spot. Such grazing might well leave areas of open, unvegetated peat, which, once dried out will again easily erode, all the while leaking carbon dioxide.
Nowadays, you may quite often see, on suitable - ie dry and fairly smooth ground - that the heather is being mowed rather than being burnt. That is certainly preferable, but not applicable over large, rougher swathes of countryside. Burning is now also more often done during a dry October (assuming we do actually have that sort of weather) which is again preferable in that it avoids any possible harm to nesting birds.
On the West, burns are generally much more sporadic, in every sense less organised, and still often undertaken in the Spring, when strong easterly winds mean that they often get out of control. Such burns often extend for miles, and leave huge areas of devastation. It is not always appreciated that while heather itself is reasonably combustible, in the wetter West where heather itself is less common, the dry molinia grass will catch fire with incredible rapidity; the conflagration spreads widely and quickly.
I did a study of muirburn in the westcoast Parish of Assynt, and mapped the burns that I could locate; recent ones were, of course, always conspicuous. The resulting map did make it clear that over the course of something over a decade, a surprising area had experienced at least one burn. Many of these in their extent and speed of travel had appeared catastrophic at the time, and one or two had threatened properties. (In one burn, a number of deer had been trapped within an area of deer-fences, and had suffered a horrible fate).
I set out to examine the effects of these burns on three specific types of terrain: the bogs, the drier moors, and the wooded places.
In these wetter places, if the climate had been fairly normal before the fire, a burn might go over a bog very quickly and lightly, consuming what little heather there was, while having little other effect. But if the bog were already dry and parched, perhaps as a result of prolonged dessicating winds, even the sphagnum moss might be blanched and singed, and it seemed sometimes to take some years to recover. This effect is crucial, as sphagnum is the surface of a healthy bog, holding water and slowly building up the depth of peat, and, of course, retaining carbon.
While it may seem unlikely that deer would try to graze such a blanched bog, they might well be tempted by fresh shoots of molinia, and just moving across ground like this might well lead to visible signs of trampling, probably causing erosion and, again, leakage of carbon dioxide to the atmosphere.
All this I had pretty well anticipated.
The result of burns on areas of dry heather, when observed over a number of years, (very easy because an extensive one was just up the road from my home), was very different. The heather and grasses burnt well and hot, and the resulting scene was, as ever ghastly. But, even during the first following year, it was clear that other flowering plants, often suppressed in the heather, were doing well: hawkweeds, slender St. John’s-wort, eyebrights, and, especially, pyramidal bugle, as well as bird’s foot trefoil, were all much more visible than before. It seemed entirely clear that the burning of the heather had the same effect on such plants as would burning of a pinewood on the birch and rowan ( discussed in ‘ Some Woodland Dynamics ‘). And, slowly, over the succeeding years, the heather took over, relegating these plants to a subsidiary role.
It can therefore be said that the occasional burn on dry ground may actually be good for biodiversity, always providing that it is not followed by heavy grazing.
Burning is often claimed as a historic way of clearing woodland, but observations in Assynt have cast considerable doubt on this notion. While I was living there, a number of fires went through areas of largely-birch woodland, and I was able to observe, over a significant period, what effect these burns actually had. On one occasion, a hot and rapidly-moving fire went through a mature birchwood, consuming dry grass, the occasional bit of heather, and dry bracken from the previous year. Some trunks were indeed scorched and blackened, but through the succeeding months, the trees, of all deciduous species, simply carried on as normal; green until the autumn. Our only tree species which burn well and then die are pine and juniper (I have no knowledge whether yew burns or not); it is pretty well possible to assess how much a suitable landscape has been burnt by the occurrence or otherwise of juniper - however, that simple picture is, I think, complicated, by juniper’s preference for particular rocks.
As I watched a number of areas of trees affected by fire, I saw that some younger trunks of birch, did, in fact, die, but the tree did not; new growth sprang from the base - ‘fire coppices’ in fact. This was a regular occurrence. I did see that seedlings and very young saplings (young regeneration) did get killed by such fires, so it should be clear that I am not claiming that such woods are not affected by muirburn passing through them; they are, but they are by no means killed or cleared. There will be microscopic charcoal in the soil profiles of such woods, but it will come from anything other than the trees.
The danger of overgrazing, whether by sheep or by deer, is, of course, still very much present, especially with the number of deer present on the West, but it did seem to me that both sheep and deer were somewhat reluctant to enter the much-larger expanses of burnt ground on the West.
While environmentalists may often call for the cessation of burning the heather right across the Highlands, there remain two problems:
1) The first is that the practice of muirburn here is something of a ritual, a traditional past-time, something which will be carried out whether there is a real reason for it, or not…………
2) And, secondly, there is the stark fact that if large areas remain unburnt for years, there will be a considerable build-up of combustible material, which will, some day, catch fire and cause a lot of damage. With the increase in the number of folk using the countryside, and in the absence of any commitment to countryside education on the required scale, this is, sadly, inevitable……..
All that it seems sensible to recommend, then, is
1) That any burning should be done in October
2) That mowing should replace burning where this is physically possible
3) That “west-coast” burning should be much more controlled
4) That “ east-coast” burning should be significantly reduced
5) That Central Government should spend a significant amount of money on countryside education, especially on the very real danger of lighting fires, portable barbecues etc.
It may be of historical interest to add here that when a detailed study of palaeoecological evidence for heathland burning was undertaken by Dr Althea Davies of Stirling University, the core taken from a site in my own glen, Glenleraig in Assynt, provided somewhat complex sequences. The location where the core was taken was where a number of rather different habitats meet: birch woodland, peaty mires beside the river, drier, more heathery moorland above, and a dry, grassy, sheiling which is now covered in bracken. There was “ a close association between heather and burning but cause and effect” were not easy to separate. “Maximum pollen values for heather coincided with a period of sustained high charcoal values around 1700-1735”. “ Following 1735, levels of burning at Ruigh Dorch declined and heather cover appears to have been reduced as a result”. To make total sense of the relationship between the two factors, burning and heather-cover, it is clear that we would need to be able to supply equally detailed climatic data. Did wetter weather set in after 1735, reducing the heather cover, and as a result the burning was reduced? And the human factor might again be important; was it an older population after 1735, meaning that less effort was made to burn the heather?
This Assynt core showed that there had been heather-burning in this glen from at least 1535 (probably much earlier), but it would be very hard to decide, on the basis of this pollen data, whether the area around had been “overburnt” as is so often claimed. I accept, as stated above, that the nearby woodland (which still exists) might have been limited by the burning of areas of young, regenerating birch, but with a population of 90 in the glen in 1774, it is probable that this burning was much more controlled than was the case in the 20th century, for instance. Only if it were possible to access a much more detailed pollen core, perhaps for all flowering species in the area, and compare the results with what grows on the ground now, could it be decided whether this part of the glen is less biodiverse now than it was then. And the effects of changing climate would have to be eliminated before it would be possible to argue that significant environmental damage had been done while the burning continued.
NB: It should be added here that I have not considered how lichens and liverworts are affected by burning, and I have no idea how quickly they might recover from it. It is certainly true that after a burn, there is a lot of charring of lichens on boulders which were “in the firing-line”. There might well be significant, long-term harm to these groups.