Blanket peat vegetation responses to burning and cutting

On each site we have four spatially separated experimental blocks looking at the vegetation and hydrological responses of burning and cutting over blanket bog. © Siân Whitehead/GWCT

KEY OUTPUTS

We initiated a long-term cut and burn experiment on five moorland sites in the northern dales.

We collected baseline data in winter 2019/20, before management treatment began, and shall continue to collect data on post-treatment vegetation responses for the next 10 years at least.

Post-treatment responses by vegetation were measured after the first growing season.

Complementary collection of data on invertebrate abundance at the experimental sites will measure food availability to grouse and waders during the critical nesting and pre-fledging period.

Siân Whitehead Madeleine Benton

In 2018, we started a study to look at the vegetation and hydrological responses of burning and cutting over blanket bog. With four treatments (burning, cutting with brash left, cutting with brash removed and no-treatment control) replicated at five sites in the north Pennines, it is planned as a long-term study to last at least 10 years. However, shortly after selecting our study sites and starting pre-treatment baseline monitoring, Natural England’s (NE) position statement on burning on blanket peat was published. Unable to secure the requisite consents for burning, we had to find alternative sites at very short notice.

Thanks to the support of landowners and keepers, we not only managed to identify alternative sites, but also managed to complete baseline vegetation surveys and get the burn and cutting treatments in place before the end of the burning season in mid-April 2020.

We now have our study up and running at five sites, spread from the North Yorkshire Dales, through Upper Teesdale, Weardale, and into Tynedale with sites offering a range of altitudinal conditions and peat depths (see Table 1). On each site we have four spatially separated experimental blocks. Each block comprises four plots, to each of which one of the four treatments was randomly assigned.

From each of these sites, we are collecting a range of data to look at the vegetation and hydrological responses to the burning and cutting treatments; this year we also conducted some preliminary investigations into the abundance of invertebrates. We collected baseline vegetation measurements over the winter 2019/20, collecting information on vegetation structure and composition as well as collecting samples of heather tips which we sent to Forest Research for analyses of nutritional content. Alongside this, we started monthly measurements of water table depth (with a subset of plots also being monitored continuously with the use of automated data loggers) and soil moisture content. Water samples are taken from some of the plots and are sent to Manchester University for determination of the extent of water discolouration and carbon content.

As soon as the burn and cut treatments had been completed, we quantified the immediate effects of those treatments (mowing height, depth of moss removed, burn severity), and we returned in autumn to look at vegetation responses after the first post-treatment growing season. As part of this, we went back to the control plots (with no experimental manipulation), to re-measure the vegetation so we can see how vegetation changes in the absence of burning or mowing.

TABLE 1

Mean (and range) peat depth and altitude of experimental burn and mow treatment plots at each of five sites. Site values are the means of all 16 experimental plots (four replicates of four treatments) at each site

Site Mean (and range) Mean (and range) altitude (m) peat depth (cm)

Teesdale 439 (434-446) 306 (185-520) Weardale 456 (365-507) 198 (105-290) Tynedale 491 (463-528) 104 (40-175) Coverdale 539 (535-543) 262 (80-350) Swaledale 629 (614-644) 198 (105-205)

In April, May and June, we sampled surface-active arthropods (mainly spiders and beetles) by sinking plastic cups into the ground (pitfall traps), to catch them. We also trialled the use of ‘emergence traps’ to get an index of craneflies emerging from within each type of management plot. These traps, comprising plastic baskets lined with sticky fly paper, are inverted and pegged down to the substrate to provide a simple, but effective means of measuring insect emergence following over-winter pupation. Although this measure will have been strongly influenced by site conditions 12 months previously, when adult craneflies were selecting where to lay their eggs, our measures provide an indication of how much of this important food source is available to grouse and waders during the critical nesting and pre-fledging period.

Initial sorting of samples shows that the most abundant arthropods caught were wolf spiders (Lycosidae) and ground beetles (Carabidae), together with bugs and flies. We also caught large numbers of heather beetles, which will form a valuable annual index of outbreak likelihood. BACKGROUND

Burning of heather on blanket peat habitat is a contentious issue. Although it can still currently be used as a tool to restore blanket peat habitat in certain circumstances, Natural England (NE) advocate the use of cutting as a preferred alternative wherever possible. However, although there have been several studies exploring moorland vegetation responses to burning, little work has been done to date to look at the effects of cutting. The biggest study, which is comparing both management treatments, is that being led by Andreas Heinemeyer (Stockholm Institute, York University). His work is now starting to yield results, but is still restricted to just three sites, which won’t be entirely representative of the diverse range of conditions across the northern uplands. Our study, also a multi-site experiment but drawing on five sites on a more northerly geographic range than that covered by Andreas’ study, will therefore complement his ongoing work by providing similar data from additional sites that are representative of a wider range of conditions of altitude, peat depth and wetness.

We collected baseline vegetation measurements, samples of heather tips to analyse nutritional content and took water samples. © Siân Whitehead/GWCT