An open meeting of the Dartmoor Society gathered in Belstone Village Hall on 20 September 2023 to hear a presentation by two officers of the South West Peatland Partnership (SWPP) Jonathan Robinson-Noades, Dartmoor Headwaters Officer and Martin Gillard, Dartmoor Headwaters Officer.
Thanks to Annabel Crowley for this report.
CURRENT APPROACHES TO PEATLAND RESTORATION ON DARTMOOR
Belstone Village Hall
Wednesday 20 September 2023
by Annabel Crowley
The SWPP is made up of 22 organisations, of which the Dartmoor Society is one. It is funded
chiefly by Natural England, with significant additional funding from South West Water (SWW), the Duchy of Cornwall, the National Trust and Cornwall Council, to undertake peatland restoration on parts of Bodmin Moor, Exmoor and West Penwith, as well as on Dartmoor.
Jonathan Robinson-Noades, SWPP Dartmoor Headwaters Officer (Peatland Restoration), is overseeing work at Ockerton Court. He began his talk by describing the process of peat formation, whereby the surface layer of sphagnum moss and other bog species gradually decomposes to form the acrotelm, or aerobic layer, beneath which lies the water table
which in turn sits above the catotelm, or anaerobic layer, with bedrock at the base. Peat forms at the rate of 1mm per year and the deepest peat on Dartmoor is up to 7m deep.
Jonny showed us a lidar (‘light detection and ranging’) image of an erosion gulley where exposed peat is washing away, contributing to a lowering of the water table and emitting
carbon in the process. By blocking such features, he said, SWPP aimed to arrest erosion and raise the water table, thereby creating the right conditions for sphagnum to colonise re-wetted areas.
The carbon stored in UK peatlands is equivalent to that stored in all the woodlands of the
UK, France and Germany combined. But where peatlands are in poor and degrading
condition, they are actually emitting carbon. Moreover, eroding peat has various adverse
effects on water quality – a matter of obvious interest to SWW, 45% of whose supply
originates on Dartmoor – including raising acidity, increasing metal concentrations,
discolouration, levels of nitrogen, sulphur, dissolved organic carbon and particulate matter.
Peat restoration work aims to hold more water on the high moor for longer and to slow its
flow in flood conditions. Simultaneously this is expected to improve the habitat of
invertebrates and increase the diversity and population of wading birds.
At Ockerton Court – a SSSi owned by the Duchy of Cornwall – Jonny explained that he uses
lidar to produce a map of the different areas and decide on suitable techniques. The site is a
mixture of blanket bog and valley mire, with some historic damage from MOD mortar shells.
Work is done in winter in order to avoid disturbing ground-nesting birds and, contrary to
what a casual viewer might expect, the vehicles are specially designed excavators that exert
less ground pressure than a human being. They also have moveable buckets that mean
movement of the polymer tracks is kept to a minimum. The contractors scan the site for
unexploded ordnance, which is logged and mapped.
Jonny ran through the various different techniques used by the team according to the
specific conditions of each site:
1 Arc bunds, made of peat: these tend to be in areas without erosion features but where
the peat is growing out. Vegetation is mostly Molinia caerulea. The bunds create small pools
that allow sphagnum, bog-cotton, bog asphodel and other species to colonise.
2 Peat bunds: mounds that trap water in peat cuttings.
3 Wool bunds: some sites possess little peat and are in poor condition. In these cases, the
project is trialling the use of wool, often from sheep that have grazed the same common.
The wool is scoured and cleaned and made into a bolster which is stuffed with more wool.
This is either laid under turf or sometimes left visible so that its effectiveness can easily be
4 Peat blocks: peat is ‘borrowed’ from adjacent intact areas to block gulleys. Sometimes
isolated hags are used in this way, since they have limited futures on their own.
5 Wooden blocks: these are used on slopes to withstand an expected flow of water. The
timber is harvested by the Woodland Trust at Fingle Woods, where conifers are being
6 Leaky wooden blocks: where water will flow too fast and in gulleys too deep to allow for
water to spread out behind blocks, leaky blocks slow down the flow.
7 Timber bunds: one or two logs deep, these are used to widen standing water in peat
8 Willow faggots: roots sprout naturally from green wood and spread to create natural
barriers and eventually scrub.
9 Stone blocks: these are planned for the south moor, where there is no peat and the base
is bedrock. Over time, the stone is expected to catch sediment.
10 Re-profiling: where peat hags are eroding, this method aims to cover up exposed peat
and top it with turf.
Martin Gillard, SWPP Dartmoor Headwaters Officer (Historic Environment), continued the
presentation with an account of the Ockerton Court works from an archaeological point of
view. His job is to walk over the site to check known features and map new ones, consult
the historic environment records, liaise with Historic England, the Dartmoor National Park
Authority and Natural England.
Long lines of turf ties at Ockerton fall into both ‘known’ and ‘new’ categories, since their full
extent became evident only recently, thanks to lidar surveys. Worked in some places on
Dartmoor up to the middle of last century and cut to run downhill so the peat cutters didn’t
stand in water while at work, these ties have exposed peat faces that are drying out. They
can now be mapped and put on record before being rewetted, their edges remaining visible
to preserve the record.
Tin streaming – the earliest and easiest way of extracting cassiterite ore eroded from veins in
Dartmoor granite – also took place on the Ockerton site, in Vergyland Coombe. Here, again,
lidar surveys and follow-up mapping show the extent of the worked area to be greater than
revealed in aerial photographs in the Historic Environment Records. Well-preserved spoil
heaps remain, as well as the remains of a building. However, some areas are beng obscured
by eroding peat and gravel, a process that may be slowed by restoration.
At the south-east edge of the site lies Huggaton Peat Pass, its sides slumped in places but
still used by commoners, and here the SWPP may do some restoration and block the gulleys
feeding into it.
Martin explained that SWPP contractors work to maps marked with ‘no-go’ areas and their
drivers are carefully briefed on the necessity for great care, since areas of eroded peat may
reveal evidence of early human activity, such as the stone row discovered in an eroded area
on Cut Hill by Tom Greeves almost a decade ago. Areas of erosion are checked as part of the
walk over; those at Ockerton did not reveal any early features.
In the questions and answers session that followed, Caya Edwards asked if coir bunds settle
in better than wool. Coir is less than ideal because of the air miles involved in bringing it
from Sri Lanka – but Jonny felt it was better at bedding into the surrounding substrate than
wool. However, he said a more formal analysis over time will be made of the wool bunds at
Ockerton Court. Wool has to be cleaned regardless of how local it is to the site, because of
current Environment Agency concerns over leaching from unwashed fleeces; discussions are
ongoing on this.
Tony Hill asked if trees could make a difference to peatland restoration and Jonny replied
that trees may have a place at the edges and in valley bottoms, since they are better
naturally than humans are at blocking watercourses, but not on the top or middle of blanket
Anthea Hooey asked if the SWPP expects more sphagnum and less molinia to result from
the project. Jonny said that monitoring is ongoing at Ockerton, using vegetation and aerial
surveys. Molinia is tough and it’s not yet clear whether submersion will kill it. It’s possible it
may be deterred by the more acid conditions sphagnum can create.
Chris Chapman asked how willow stands can develop on the open moor where stock can eat
the young plants. Jonny replied that the SWPP has acquired permissions to fence such areas
for up to five years in order to protect the willow while it establishes.
Asked about the likelihood of reprofiled areas being poached by cattle, Jonny said the
project would aim to repair any damage where they were still operating in the site. Future
maintenance will be the subject of discussions with the landowner and/or the graziers.
David Hill asked if restoration work will result in water levels being lower in Dartmoor’s
rivers. Jonny said the amount of water overall would be the same but the aim was to help
the high moor to hold it for longer and release it more slowly.
At the end of the session, I asked Jonny about the optimum depth of pools for sphagnum
regeneration. He said that shallow water was best but that sphagnum would gradually grow
out from the edges of deeper pools too.