By Tim Baynes, Moorland Director at Scottish Land & Estates

The role of muirburn in maintaining some of Scotland’s most precious habitats can be heated one – but new science from the University of Cambridge is the latest research to demonstrate the importance of ‘cool burns’ to our upland ecosystem.

Published in Nature Geoscience by Dr. Adam Pellegrini and colleagues from the institution’s Department of Plant Sciences, the study finds that prescribed burning can actually lock in or increase carbon in the soils of temperate forests, savannahs and grasslands.

The authors detail how fire burns plant matter and organic layers within the soil, and in severe wildfires this leads to erosion and leaching of carbon. It can take years or even decades for lost soil carbon to re-accumulate. But the researchers say that fires can also cause other transformations within soils that can offset these immediate carbon losses, and may stabilise ecosystem carbon.

Without fire, soil carbon is recycled – organic matter from plants is consumed by microbes and released as carbon dioxide or methane. But infrequent, cooler fires can increase the retention of soil carbon through the formation of charcoal and soil aggregates that protect from decomposition.

The scientists say that ecosystems can also be managed to increase the amount of carbon stored in their soils. Much of the carbon in grasslands is stored below-ground, in the roots of the plants. Controlled burning, which helps encourage grass growth, can increase root biomass and therefore increase the amount of carbon stored.

The University of Cambridge study is a hugely important contribution when the role of prescribed burning has been under the spotlight through the continuing debate on moorland management – not to mention the climate emergency and COP26.

Yet, this study is the latest to come to similar conclusions following research by academics at Lancaster University, the University of York and Newcastle University.

In May 2020,  research published by Duke University in North Carolina, USA, concluded high-intensity fires, such as wildfires, can destroy peat bogs and cause them to emit huge amounts of their stored carbon into the atmosphere whilst low-severity fires – such as muirburn – spark the opposite outcome.

So why does the Cambridge research matter when considering the future of Scotland’s land management?

Despite heather burning already being regulated in line with the Muirburn Code, it continues to attract opposition from anti-grouse moor activists who claim halting the practice would reduce carbon emissions.

Yet, their opposition to heather burning is often confused in its outlook. Some activists and pressure groups have chosen to disregard the science being published over previous years. Instead, they opt to term the practice as ‘peatland burning’ and try to imply that managed muirburn burns the peat – it does not; it only takes off the top layer of vegetation which then regrows and locks up carbon again.  This is clearly demonstrated in two muirburn films on the website of Scotland’s Regional Moorland Groups.

There are undoubted benefits to grouse moors in conducting rotational heather burning, which provides new heather for wildlife – including red grouse – to eat and longer patches of heather to take shelter in.

But now, a steady stream of science is also showing that cool burns are good for our ecosystem and for capturing carbon – especially when they aid the fight against the increasing threat from wildfires.

Scotland has witnessed some huge wildfires in recent years, including the uncontrolled fire on peatland on part of the Flow Country which is estimated to have released carbon into the atmosphere equivalent to six days’ worth of the nation’s total greenhouse gas emissions (according to WWF).

In countries with higher temperatures, such as Australia, the USA and Spain, controlled burning has been practised to prevent wildfires. Domestically, the Scottish Fire & Rescue Service has recently endorsed it as an important land management tool to reduce fuel load and avoid the sort of ferocious blaze witnessed in the Flow Country in 2019.

The latest research from the University of Cambridge adds to a bank of academic output which demonstrates the value of controlled burning in not just lessening the risk of high carbon emissions from wildfire but actually increasing carbon storage through use of fire. Whilst that may seem a paradox to many, if we are to produce the best public policy for our uplands in future then it would be useful to follow the science on this matter and hopefully enable the heat to be taken out of the debate in the process.