Effects of rotational prescribed burning and sheep grazing on moorland plant communities: Results from a 60‐year intervention experiment

Abstract

The effect of prescribed burning for conservation management of plant communities is controversial for moorlands growing on peat. These ecosystems provide many services that may be damaged by fire, hence it is important to fully assess its impact on all aspects of ecosystem structure and function experimentally over relatively long time‐scales. This paper describes change in community composition, major plant species, and plant functional types on moorland on peat in upland Britain over 60 years subject to 3 burning treatments after an initial burn in 1954/1955: no further burn and burning at 10‐ and 20‐year intervals (all ± sheep grazing). Data were analysed using multivariate and univariate methods. Vegetation composition and individual species abundance reflected the degree of disturbance. The least disturbed was dominated by Calluna vulgaris and pleurocarpous mosses, whereas the most disturbed treatment (burned every 10 years) had greater Eriophorum vaginatum, Sphagnum spp., acrocarpous mosses, liverworts, and lichens. The 20‐year treatment was intermediate in response disturbance. Repeated burning increased species abundance‐weighted Ellenberg values for moisture, reaction, light through time, and fertility; the exception was the 10‐year rotation for fertility. These confirm that prescribed burning is not deleterious to peat‐forming species (Eriophorum spp. and Sphagnum spp.), indeed these species were found in greater abundance in frequently burned treatments. It also confirms that a no‐burn policy will lead to increasing dominance of C. vulgaris, a flammable, fire‐adapted shrub, which increases summer wildfire risk. These results inform conservation management policy for moorland vegetation growing on peat; for this site, a 20‐year prescribed burning rotation is recommended.

Effects of removing sheep grazing on soil chemistry, plant nutrition and forage digestibility: Lessons for rewilding the British uplands

“…There latter suggests are three potential constraints to the colonization by new species, a lack of (1) propagule availability, (2) regeneration niches (sensu Grubb, 1977), and (3) the small size of the experimental plots (Milligan et al, 2016). In terms of new colonists there has been no colonization by tree species in any of these experiments (Milligan et al, 2016), although in another, larger, long-term experiment at this site (Milligan et al, 2018) one small Betula sapling persisted for some time then died, and a few Picea sitchensis seedlings have been detected recently after a period of ca. 60 years grazing-free (R.H. Marrs pers.…”

Contextualising UK moorland burning studies: geographical versus potential sponsorship-bias effects on research conclusions

“…The test was unconditioned because rows and column totals varied. The test assumes independence of observations between each published study; this might not be the case for some long-term studies such as those reporting vegetation changes over time at the Moor House experimental plots in northern England (Milligan et al, 2018, Marrs et al, 2019b, Lee et al, 2013) but here we assumed them to be independent because each successive study reported new observations.…”

“…For Sphagnum growth/abundance specifically, four papers with grouse industry funding links have suggested positive effects but none have suggested any negative effects, in contrast to 6 negatives and 5 no/mixed effects funded by non-grouse shooting organisations. All four of those positive papers (Lee et al, 2013, Marrs et al, 2019b, Milligan et al, 2018, Harris et al, 2011 are from the same research group, whose long-time head is the President of the Heather Trust, a pro-burning, grouse industry group. Three of those four papers reported results from the same experiment undertaken at the Hard Hill burning plots at Moor House, northern England.…”

Whither scientific debate? A rebuttal of “Contextualising UK moorland burning studies: geographical versus potential sponsorship-bias effects on research conclusions” by Brown and Holden (bioRxiv 2019; 731117)

“…Another significant failing of B&H's analysis is the lack of statistical independence. For example, Lee et al (2013a), Marrs et al (2019) and Milligan et al (2018) were included as three independent data points during the analysis of bias within grouse moor industry studies. However, all three studies use the same vegetation data from the same experiment, which means they are not independent.…”

“…the conclusions) rather than on the results presented. For example, Lee et al (2013a), Marrs et al (2019) and Milligan et al (2018) are classified by B&H as finding a positive effect of burning on Sphagnum growth and abundance, but the results sections of these studies indicate that burning had a mixed effect on Sphagnum, with the direction of the effect depending on time since burn (ibid). It seems odd that researchers would quantify the effects of a study based on its conclusions.…”