By Teresa Dent CBE, GWCT Chief Executive
The recent call from RSPB to ‘stop burning the peat’ seems to deliberately confuse controlled and uncontrolled burning. Its press release makes 6 references to burning peat, peatland and blanket bog, all in connection with management practices and consents that are actually for the controlled burning of heather (surface vegetation) not peat (the underlying soil).
Does this matter? Yes – a lot.
Controlled burning of surface vegetation is only permitted to take place in the winter (cold and wet), is deliberately limited to small areas (the Heather and Grass Burning code suggests a maximum of 30m by 600m) with cut margins as fire breaks surrounding them, and a fire-fighting team of gamekeepers in attendance with fire fogging units and leaf blowers to extinguish flames quickly.
This is what is called a ‘cool burn’, a technique adopted widely after 2007. That might sound like an oxymoron but describes it well. The fire burns quickly through the surface wind-dried vegetation but does not penetrate the winter-damp litter layer and moss on the surface of the peat, or the even-wetter peat itself. They do not even get hot. We know because GWCT conducted experiments with expensive temperature probes in 2004.
Geoff Eyre, one of the most knowledgeable people in the country on peatland, illustrates this much more inexpensively when he is cool burning. He puts a 60p Mars bar on the peatland surface and covers it with an inch or two of the litter layer. After the cool burn has gone over, he immediately extracts the Mars bar, which is not even melted.
Yes, this controlled, cool, winter, consented burning is done to create mixed-age stands of heather so that red grouse (a game bird which exists on a diet almost entirely of green heather shoots) can eat well. It is also done to help prevent uncontrolled burning or wildfire; the burnt areas act as natural firebreaks.
A good third reason for doing it is that having areas of short/ burnt vegetation also favours some of our favourite uplands birds, curlew, dunlin and golden plover. GWCT scientists have found 6 times as many of them on areas with controlled burning than no burning.
Uncontrolled burning is a wildfire that usually takes place in the summer (hot and dry), often started maliciously or accidentally, and as we have seen in recent years can spread alarmingly rapidly both in extent and depth. This is the fire that burns the peat – or more accurately the surface vegetation, moss and litter layer and often the peat beneath it as well. And, as we have seen, is difficult, time-consuming and downright dangerous to put out. This is where fighting the fire becomes like California – another fire-prone eco-system.
So if we are worried about carbon emissions as a result of burning, where is the carbon? Natural England did a review of carbon storage by habitat in 2012. That concluded that dwarf shrub heath had 88t of carbon per ha in the peat and 2 tonnes in the vegetation. Bog had 74 and 2 respectively. Both represent heather moorland, so let’s say the peat carbon is an average of 81 tonnes per ha. That would be about 3 large lorry loads of carbon per hectare . The 2 tonnes in the vegetation would be about 2 cubic metres, or 2.4% of the habitat carbon.
Then let’s ask ourselves how much of the vegetation actually gets burnt in a controlled, cool, winter, consented burn. My friend Geoff Eyre worked that out for me. He took a number of m2 samples of vegetation before a cool burn, and similar number of m2 samples afterwards. The cool burn did not burn the heather to the ground, it removed the leaf area, smaller stems and left a lot of what keepers call ‘stick’, the thicker stems and the trunk. By weight this was 75% of the unburnt vegetation, so only 25% of the carbon in the vegetation was released in the burn.
Clearly none of us wants the peat to burn - let alone, God forbid, all 81 tonnes of carbon per hectare – 97.6% of the carbon in that habitat with its associated locked up heavy metals and pollutants drawn from our industrial past’s atmosphere. The RSPB does not want that, nor Defra, nor the grouse moor owners. After all the peat supports the heather plants that their grouse eat. We have seen that controlled burns burn vegetation, but uncontrolled wildfire can burn peat.
So how do we help prevent wildfire? Stopping people maliciously or accidentally setting fire to it is one thing. Natural firebreaks - always previously burnt areas though now people are trying to find out whether cut areas act as good firebreak too. Existing tracks and again pre-burnt areas of low fuel load give safe access as the flame height diminishes. Often the first and last fire-fighters on the scene will be the game keepers. Lastly re-wetting can help mitigate the damage a wildfire does below ground – but that is the subject of another blog.
How should we use controlled burning to reduce the severity and spread of wildfire? The England and Wales Wildfire Group has just produced recommendations on how to design a controlled burning, wildfire-prevention policy on moorland. A moor I know has produced a fire mitigation plan in line with these recommendations which would result in the moorowner undertaking cool, winter, controlled burning on 7.7ha of vegetation to help protect 500ha of peat from the risk of burning.
So, lets do the carbon equation on that. To help protect 41,500 tonnes of carbon in 500ha of both peat and vegetation, he wishes to cool burn less than 4 tonnes of carbon in vegetation (3.85t to be exact). That is 0.01% of C lost as insurance. And that is in the year he burns the firebreaks: if the firebreaks last 2 years you can halve that figure; 4 years and you can halve it again.
That feels like a very sensible management policy to me, especially as the carbon released by burning is only the carbon that those plants have stored up during growth through photosynthesis. Those plants will grow again in a decade or two, so in that time scale it is carbon neutral; Liverpool University estimated that the Saddleworth Moor wildfire resulted in seven centimetres of peat being lost, and that it will take up to 200 years to restore.
Our next blog will look at whether controlled, cool, winter burns do actually prevent carbon accumulating in peat, or dry it out, or prevent blanket bog from being restored.