There is no one-size-fits all approach to heather management; but all tools must be available
A report released today by the University of York has declared that there is no ‘one size fits all’ heather management method for protecting carbon-rich peatlands.
The document has been produced at the ten-year point of a 20-year study that compares the impacts of different management options on key aspects for mitigating climate change, increasing water storage and quality, as well as supporting biodiversity.
Researchers at the Stockholm Environment Institute (SEI), based at the University of York, found that heather burning, mowing or leaving it unmanaged should all be available tools that upland land managers can use. The method used should be determined by the condition of that particular piece of land and particular aspects. Vitally, there was no ‘one size fits all’ approach. This is not the first study of moorland management methods. But vitally, there have been no other studies designed to go into so much detail, and over such a length of time. The fact that we are ten years into this landmark twenty-year study means that the longer-term effects of the various management methods will be shown, rather than just the short-term ones.
For example, the study has so far shown than after initially releasing carbon, burnt sites now take up and store the most carbon per year. Mown and uncut sites both absorb about half the carbon per year of burnt plots. The current predictions from this study suggest that uncut plots will gradually absorb less and less over the next decade, whereas mown and burnt plots will likely keep absorbing at similar levels for a considerable time. However, a longer-term study such as this is needed to find out this information.
Associate Professor Andreas Heinemeyer, from the SEI, said that:
“After ten years our ongoing study on peatland management is finally providing some of the answers on how heather burning compares to mowing or uncut approaches. Concerns around burning, for example, are often focused around the large emissions from fire, but we found that whilst carbon loss from the burnt areas is higher in the short-term than from mowing, it then falls as vegetation regrows and takes up a lot more carbon.
“From mowing you lose a lot of carbon in the long-term as the brash decomposes, which confirms previous modelling studies. There is a growing body of evidence that burning management approaches can play a more important role in carbon sequestration than previously thought.
“After about six years the predicted carbon balance for the burnt plots showed a carbon sink and over the 10 years it absorbed more than twice the carbon compared to mown areas.
“If we compare this to unmanaged heather areas, we find that although they soak up most carbon over the course of our study, over time as the heather ages, it becomes less efficient in taking up carbon and these areas also get drier, allowing microbes to decompose the peat. As a result, uncut areas absorb less than half the levels compared to at the start of our project.”
Prescribed burning has long been the most demonised and polarising method of managing heather and surface vegetation, but this study showed that burning in particular was good for nutrient content for grazing animals but also for carbon uptake, likely due to the fertilisation that ash provides. Mowing benefitted peat wetness to a small extent, but the additional benefit only lasted a few years after mowing.
The study showed that the burning and mowing of small patches of heather supported increased vegetation diversity, with increased levels of sphagnum moss compared to uncut plots. The study also predicted a greater number of some ground-nesting birds on burnt and mown plots, as the taller heather limited appropriate nesting sites.
The topic of rewetting of peatlands is another subject inclined to inflame debate. This study has, so far, shown that in areas where heather was not managed but was left to grow, water tables gradually dropped throughout the project. This means that the peat dried out – which is when they begin to release carbon. Average yearly water tables began at about 11cm below ground level and dropped to about 13 cm during the last three years.
Mown plots became wetter in the first few years after mowing, rising during summer by about 2 cm compared to burnt plots. However, compared to initial levels, the burnt plots subsequently showed the most rise in water levels in recent years, but with more variability between seasons than mown plots.
The fact that unmanaged plots appear, in the long-term, to lead to the drying-out of peatland begs the question why so much money is being spent on the rewetting of peatlands. A quick look at the accounts of the Peak District National Park Authority shows that in 2019/20, the authority received £4.8million from the Moors for the Future Partnership towards the rewetting of peatland. At the same time, areas of the PDNP are clearly being unmanaged.
The study shows that unmanaged plots will dry out; so this £4.8million is, in many areas where the peatland is rewet but then left unmanaged, literally being flushed away. The current fashionable mantra appears to be that peatbogs must be rewetted; but in fact it appears that in many upland areas, traditional moorland management does as much for the rewetting of peat bogs as the well-funded peatland rewetting projects – if not more!
Another vital role that the management of moorland fulfils is in the control of wildfires. This year saw a big rise in summer wildfires across the country, both on moorlands and areas of grassland, but also in more urban areas. Fire services in England dealt with nearly 25,000 wildfires in the summer of 2022, almost four times the number of summer 2021 and the highest for this period in at least a decade.
Scientists have warned that they suspect this trend is likely to increase, with heatwaves becoming more frequent in Northern Europe. Worryingly, “wildfire is a rather unrecognised hazard in the UK”, said Nigel Arnell, professor of climate system science at the University of Reading. “While we might not see the sorts of forest fires sweeping through Spain, Portugal and France, we are increasingly prone to fires in grassland and moorland that have the potential to affect people, property and infrastructure as well as the environment.”
Moorland management performs two roles from a wildfire perspective; firstly removing excess surface vegetation which acts as a fuel load when wildfires do break out. Secondly, burning or mowing the vegetation creates fire breaks which stop a wildfire in its tracks. It is vital, therefore, that these management tools should be available to those whose job it is to manage the moors.
The full report and further information from the University of York can be found here: https://www.york.ac.uk/news-and-events/news/2023/research/heather-management-protecting-peatlands/