Heather burning – GWCT responds to criticisms

By Andrew Gilruth, GWCT Communications Director

It has come to our attention that an RSPB presentation, delivered to raptor study groups last November, accused the GWCT of “distorting and discrediting the science” around heather burning^a. We reject this.

We feel we have accurately and openly reported the breadth of evidence available. The fact we have not reached the same conclusion as the RSPB does not amount to distortion. Disagreement and challenge is a normal part of the scientific process.

What has the GWCT said about heather burning?

A month before the presentation in this video the GWCT had stated the following in our submission to the Petitions Committee inquiry into grouse shooting:

“There remains contradictory evidence about the actual positive or negative impact of burning when longer time-scales are taken into account¹. More research is needed.” 

What did the RSPB say to the inquiry?

Their submission is here and, during the oral evidence session, Rishi Sunak MP asked the RSPB witness: “Where have you seen examples that there are conservation benefits from selective vegetation burning?”

Rather than answer the question, the RSPB said that they see heather burning as an “an environmental ill” and “a net negative [environmental] impact”.

This may be their view, but the scientific literature is conflicting and there is not yet a consensus to back such a generalisation. As with most management practices, if it is done incorrectly it can be damaging; however, used appropriately it can be an effective management tool with conservation benefits.

How did the GWCT respond at the time?

Since the GWCT felt that comments made in the oral evidence were not supported by the evidence base, we submitted supplementary information including the following^b:

“The evidence on burning is highly contested; this is demonstrated by the high level of debate amongst 16 scientists from six nations in recent exchanges in the journal of the Royal Society, the world's longest-standing scientific society. They agree that more research is needed here. Examples of the wider debate include: 

1)  Peat formation – as well as negative impact there is also evidence that burning heather has a positive impact on the Sphagnum mosses that are important in peat formation². The authors “found no evidence to suggest that prescribed burning was deleterious to the abundance of peat-forming species; indeed, it was found to favour them”.

2) Dissolved Organic Carbons (DOC) – There is also some evidence that DOC levels are unaffected or decline where burning has taken place^3,4.

3) Water table – the EMBER study suggests heather burning lowers the water table, others suggest it does the opposite^3,5,6.

4) Scale of burning – some authors express concern that more burning, rather than less, should be occurring, to reduce potential fuel build-up and wildfire risk⁷. Recent evidence from the Peak District shows that burning is generally carried out in accordance with guidelines, with appropriately sized burns and only 0.9% area being burnt per year, well below the recommended 10%. 

5) Carbon budgets – a Natural England evidence review assessed that the evidence for overall carbon budgets is limited and contradictory⁸. 

6) Flooding – a Government committee report does not implicate increased burning in increased flood risk⁹.

There is contradictory evidence. For instance, the EMBER study also suggests overland flow is less common on burnt peat than unburnt peat. For the lowest 80% of rainfall events, the lag period is greater on burnt areas, and there is no difference for the top 20% (heaviest storms). For the top 20% of storms, the hydrograph intensity is higher for burnt areas but the lag time is not affected. This means that the peak discharge (amount of water in the stream), is higher for these heavy storms, but it does not happen faster¹⁰.  

This is precisely why the GWCT feels more research is required, before advocating wholesale changes to a land management tool that may be supporting the very biodiversity that we are all striving to protect.

A wider GWCT summary of the available evidence on a wide range of moorland management issues, including heather burning, can be downloaded here.

If you would like to read a copy of our submissions to the 2016 Westminster grouse inquiry, it can be found here. 

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References

1. Clay, G. D., Worrall, F. & Aebischer, N. J. Carbon stocks and carbon fluxes from a 10-year prescribed burning chronosequence on a UK blanket peat. Soil Use Manag.31, 39–51 (2015).

2. Lee, H., Alday, J. G., Rose, R. J., O’Reilly, J. & Marrs, R. H. Long-term effects of rotational prescribed burning and low-intensity sheep grazing on blanket-bog plant communities. J. Appl. Ecol.50, 625–635 (2013).

3. Worrall, F., Armstrong, A. & Adamson, J. K. The effects of burning and sheep-grazing on water table depth and soil water quality in a upland peat. J. Hydrol.339, 1–14 (2007).

4. Clay, G. D., Worrall, F. & Fraser, E. D. G. Effects of managed burning upon dissolved organic carbon (DOC) in soil water and runoff water following a managed burn of a UK blanket bog. J. Hydrol.367, 41–51 (2009).

5. Clay, G. D., Worrall, F. & Aebischer, N. J. Does prescribed burning on peat soils influence DOC concentrations in soil and runoff waters? Results from a 10year chronosequence. J. Hydrol.448–449, 139–148 (2012).

6. Clay, G. D., Worrall, F., Clark, E. & Fraser, E. D. G. Hydrological responses to managed burning and grazing in an upland blanket bog. J. Hydrol.376, 486–495 (2009).

7. Allen, K. A., Denelle, P., Ruiz, F. M. S., Santana, V. M. & Marrs, R. H. Prescribed moorland burning meets good practice guidelines: A monitoring case study using aerial photography in the Peak District, UK. Ecol. Indic.62, 79–85 (2016).

8. Glaves, D. et al.Natural England Review of Upland Evidence 2012 - The effects of managed burning on upland peatland biodiversity, carbon and water. (2013).

9. Committee on Climate Change. Written evidence to the Inquiry on Soil Health. (2016). Available here. (Accessed: 28th October 2016)

10. Holden, J. et al. Impact of prescribed burning on blanket peat hydrology. Water Resour. Res.51, 6472–6484 (2015).