- Blanket bogs are nationally important habitats that host a wide range of specialist species and are important for carbon capture and water storage.
- Prescribed burning has historically been used to manage heather habitat in moorland environments but, after changes to regulations, heather cutting has become more widely used.
- This study set out to assess the short-term effects of heather cutting on blanket bog vegetation, including mosses.
- Heather cutting reduced the overall vegetation height but led to a significant decrease in the depth and variation in the moss layer.
- Long-term monitoring is needed to further assess the effects of heather cutting on blanket bog vegetation before it can replace burning as a moorland management method.
UK peatlands are of national and international importance for biodiversity and for their value to society and the economy. Most UK peatlands are blanket bogs, which are rain-fed, acidic, waterlogged habitats where dead plant materials naturally accumulate and eventually form peat. Blanket bogs capture and store carbon, and support specialised plants and animals, many of which are only found in these habitats and some of which are rare and declining. Beside heather and other taller vegetation, blanket bogs have a moss layer. This moss carpet, of which Sphagnum mosses are an important part, forms a protective layer over the peat and helps to prevent drying or erosion.
Until recently, prescribed burning has been a widely used tool to manage vegetation on heather-dominated moorlands. This is done to maintain a mosaic of vegetation ages and heights. This variation helps to support a wide range of wildlife, with higher numbers of red grouse, golden plover, curlew, whinchat and lapwing found where patch burning has resulted in a mix of taller, older vegetation for shelter, and younger, shorter vegetation providing plant and insect food resources.
In 2021 English regulations were updated to restrict burning of heather on blanket bogs following research reporting negative impacts of this burning. There is still uncertainty about some of these impacts as some studies suggest that regular burning helps to maintain and promote diverse plant communities, including the moss layer. It is likely that the burning frequency, level and type of grazing, and amount of air pollution also influence the moss layer.
This restriction on heather burning has led to an increase in heather cutting. This method of management is relatively under-researched, with only a few studies looking at its effects, and even fewer looking at those effects on deep peat habitats. The increasing reliance on heather cutting means that more research is needed to better understand its effects. This study adds to the knowledge base on heather cutting to support informed, evidence-based management decisions.
What they did
The scientists studied vegetation on two red grouse moors in Upper Teesdale, in northern England. Both sites had at least 60 small plots where mature heather was cut in the winter of 2020/21.
From these cut plots, ten randomly selected plots (minimum 5m by 8m) were assessed on each of the two moors. Each of the selected plots had an uncut ‘control’ plot immediately next to it to allow for comparison. The cut and control plots were assessed in spring 2021. In each plot, the scientists took 44 moss depth measurements along transects to provide a measure of moss microtopography (‘hummocks and hollows’). They also measured the percentage cover of different kinds of moss and the height of other vegetation present in each plot.
What they found
Measurements from the uncut control plots showed that vegetation height was an average of 10cm taller on one site than on the other, and there were distinct differences in the proportions of moss types between the two sites.
Following cutting, the moss depth, microtopography, and vegetation height in the cut plots were significantly lower than in the uncut plots. The amount of some mosses was also much lower after cutting had taken place. Across both the study sites, moss depth was 40% lower and vegetation height was 62% lower after cutting.
What does this mean?
This study shows that in the six months following management, heather cutting led to an immediate decrease in depth and structural variation of the moss layer. These short-term effects may influence the future functioning of the blanket bog habitat.
While the heavy machinery used for cutting likely caused some compression of the moss layer, it was clear that cutting had ’scalped’ some of the Sphagnum mosses while other mosses had been completely removed in some places. Damage to the Sphagnum mosses, by removing their growing tips, may limit the ability of the moss layer to regenerate. However, if the cut material is left scattered on the plot there is potential for regeneration from remaining moss fragments. Regardless of the size or complexity of the moss hummock and hollow structure that was present before cutting, the machinery left behind a largely flat, uniform surface, removing many micro-habitats that would otherwise be used by a variety of plants and animals.
Given how important healthy moss layers are to functioning blanket blogs, it is vital that long-term monitoring of cut plots is conducted. Further research is needed to find out if altering the cutting height can reduce impacts on the moss layer while still removing enough of the heather canopy. As cutting becomes a more widely used management method, it is also important to consider the influence of machinery type, heather age, and cutting frequency to monitor effects on the carbon capture, water storage, and biodiversity.
To be a sustainable alternative to heather burning, the negative effects of heather cutting need to researched and mitigated by benefits to land management. This needs to be considered in relation to the emerging evidence around the effects of burning so that management practices can be evidence-led.
Read the original paper
Holmes, K., Whitehead, S. (2022) Immediate effects of heather cutting over blanket bog on depth and microtopography of the moss layer. Mires and Peat, volume 28, article 25, pp.11