Dartmoor’s blanket bogs


Reading Tony Whitehead’s piece in West Country Voices (‘Failing nature on Dartmoor‘ ) exploring some of the realities behind the outpouring of protest from the farming industry and lurid claims that Natural England has a secret (and no doubt cunning) plan to “rewild” Dartmoor, has enthused me sufficiently to write a blog.

I don’t intend for this to be a long a discursive blog (of the kind I used to enjoy churning out) as I am still struggling with chronic migraine and I just won’t be able to do so. Another annoying thing is that it has affected my typing. So apologies in advance if you spot any typos or, more likely, weird autocorrect errors. [If they are still there, we missed them, too! Ed]

Tony set out very eloquently what the issues are with Dartmoor, the SSSI, and grazing. I see no point in going over the same ground. But I did think it was worth just expanding a bit on Dartmoor’s blanket bogs. Dartmoor is very unusual in supporting a substantial area of blanket bog, due to the very high annual rainfall amounts that it receives – and its topography.

Those of you who are big fans of English temperate rainforest, will note that the same combination of climate and topography leads to either Atlantic forest or blanket bog. I digress.

Blanket bog is a habitat which comprises different layers of peat, with a vegetated surface. By definition, Blanket bog only occurs where there is more than 40cm of peat below the surface vegetation. If there is peat, but less than 40cm, the habitat is, again by definition, called wet heath. I had an interesting visit to Dartmoor about 10 years ago, where I met a number of Dartmoor commoners, and they were all surprised to discover that this was the only way of differentiating (at the margins) wet heath from blanket bog.

Of course, healthy actively growing blanket bog supports a different set of plant species from Wet Heath. This includes different species of sphagnum moss, also known as bog moss. Various different kinds of cotton-grasses are also more likely to occur on blanket bog than wet heath, as well as a range of other plants. But at the transition between the two – and, especially important for Dartmoor, where blanket bog and wet heath have been damaged by a range of human activities, it does get messy. But the simple task of sticking a pole into the peat and measuring its depth provides a simple solution to where the blanket bog is, and where the wet heath is.

This may all seem quite esoteric and far removed from the realities of agriculture on Dartmoor.

But believe me it is very important.

The image at the top of the page is a vegetation map of Unit 87 of Dartmoor North SSSI (from the Dartmoor Farming Futures document, produced to support the implementation of the Forest of Dartmoor Higher Level Stewardship (HLS) agreement).

Here it is again, showing the SSSI units and their condition (courtesy of MAGIC).

As you can see it’s coloured orange, which stands for “unfavourable no change.” This is the heart of the northern section of the Common known as “the Forest of Dartmoor” and it’s the Forest of Dartmoor and the HLS agreement, with its circa 80 active commoners, which has been in the news so much. If you want to read more about The Forest of Dartmoor and Dartmoor’s other commons, take a look at Guy Shrubsole’s blog on the matter.

Most of Unit 87 is blanket bog (blue on the first map). In fact, the majority of the Forest of Dartmoor is blanket bog. According to the HLS agreement the figure is around 6850 hectares, or around 61 per cent of the total area (11200 hectares).

This is not pristine blanket bog, far from it. Dartmoor’s blanket bogs have been very badly damaged over a long time period. Peat cutting started in mediaeval times and was only halted in the 1950s. Peat was cut to heat domestic houses, but in the main it was cut to provide fuel for the tin industry. Industrial quantities of peat were cut and transported to Cornwall where the tin smelting has happened back into pre-history. Dartmoor also had its own tin industry and peat was cut to fuel this, too.

To fuel the tin industry, peat was converted into charcoal after it had been dried. This was done on the high moor next to the tin smelters. It was a skilled enterprise undertaken by those who became known as the Carbonarii, and records of their activities go back to the 13th century, including a Charter by King John in 1201, though the activity may go back some way further.

In more recent times, speculative peat extraction reached a zenith in Victorian times, when naive investors could be quickly parted from their money by shysters.

Dartmoor’s massive peat accumulations (some of which are at least 4000 years old) have been mined and exploited for well nigh a thousand years just for the tin industry. In more recent times, efforts have been made to drain the wetter areas to enable more grazing to be created, often with government subsidies. So the blanket bog has dried out, destroying the valuable wildlife habitats. Drying peat also releases greenhouse gases like methane and carbon dioxide; and it only creates poor quality grazing. As it dries it’s also vulnerable to further damage by wild fires or controlled burning called swaling. The consequence of this is that most of the damaged peat is now covered by purple moor-grass, which Tony talked about in his article.

Restoration of Dartmoor’s blanket bogs is essential for a number of reasons. Firstly, it’s an internationally important habitat currently protected under the EU Habitats Directive. Secondly, it has the capacity to sequester a truly mind-blowing amount of carbon dioxide. Perhaps most importantly, though, is that this incredible wild landscape will be restored, for wildlife and people alike.

But what about grazing and the commoners? Blanket bog is very sensitive to grazing and active blanket bog actually doesn’t need grazing at all: even light amounts of grazing, at the wrong time of year, can damage it. Restoration of blanket bog is really all about restoring its hydrology, by blocking up drains and reprofiling (with diggers) areas which have been left badly damaged by past peat extraction. There’s a very exciting project already happening on Dartmoor led by the South West Peatland Partnership, using timber cut from The Woodland Trust’s Fingle Woods project. The current plan is to restore 1000 hectares, but it really needs to encompass all of the blanket bog.

The controversial proposal to reduce commoners’ stock on the Forest of Dartmoor isn’t controversial when you realise just how much of the Forest of Dartmoor is blanket bog (albeit damaged) and how few stock it should be supporting. The figures that Natural England are working from are 0.035 livestock units(LU)/hectares(ha)/year(yr) for maintaining healthy blanket bog, but only 0.018 LU/ha/yr for restoration.

A Dartmoor Pony might be 0.75 of an LU, so the 2000-2100 hectares of blanket bog in unit 87 might only sustain 48 ponies all year round, or 25 ponies all year round plus 34 cattle from march to August. These figures do sound tiny, but they reflect the fact that so much of the high moor is blanket bog and is not suitable for grazing, or at least not the levels of grazing on the commons to which the Commoners have become accustomed.

The question is: how does society value Dartmoor? As a resource to be cherished and protected, providing benefits like storing carbon, having thriving populations of wildlife, providing clean water, but also more intangible things like wonder and relaxation?

Or do we just see it as somewhere to be exploited and damaged, as it has been for millennia?

You can read more articles by Miles here.