Wednesday, 15 June 2016

13th June 2016. The day I learned about managing Culm grassland.

It's raining. Great drenching sheets of the stuff, blowing in waves across the garden to the point where, when I look out of the window, I can't see the trees two fields over.

Even Rosie refuses to go out. She looks at me with that slightly questioning look that means 'You seriously expect me to go out in that?' and 'Got any food?' both at once. Although actually,  every look from a Spaniel means 'Got any food?, so there's nothing new there.

On this particular day, though, I can't blame her. So while she goes to sleep on a big cushion next to my desk, I sit down at the computer and decide to take the opportunity to find out a bit more about Culm grassland and the way it's managed at Volehouse.

The first and most surprising thing I learn is that Culm grassland is confined to the area between Dartmoor, Exmoor and the Atlantic coast. It's a unique habitat, that lies on top of the Culm measures that are only found in this tiny area of the UK. It's so special that the main culm basin has been subdivided into its own specific sections- the Holsworthy group and the Teign valley group, AKA the Lower Culm.

Location of Culm grasslands in UK (JNCC)

The Holsworthy group is further subdivided into the upper Bude formation and the Crackington formation, the Bideford formation and the Launcestone formation. I'm not exactly sure where the boundaries lie, so I can't say which camp Volehouse falls into but I'm assuming it must be Bideford . Anyway, it's all part of the Culm measure.

According to Wikipedia, Culm measure is the name given to a particular geological strata that stems from the Carboniferous period, 300 million years ago.  It's called Culm because it gives rise in certain areas (notably around Bideford, Barnstaple and Hartland) to soft, sooty deposits of coal, known in the local dialect as 'culm', which itself probably derives from the Welsh word 'cwlwm' meaning 'knot', on account of the folding pattern of the beds in which this soft coal is found.

As a lover of trivia, this stuff is meat and drink to me and it's still chucking it down, so I push on.

It seems that the Culm measures also consist of shale, sandstone, slate, limestone and chert.


Yes, I thought that, too. It's a 'fine-grained, silica-rich microcrystalline sedimentary rock that may contain small fossils'. Is there no question that Wikipedia can't help with?

It's on top of all this culm and, er, chert that Culm grassland forms. It's a species-rich habitat, characterised by moor grass and rush pasture- hence it's other name 'Rhos pasture'. It's a heavy, acidic soil, poorly draining, which has been used mostly for grazing historically, as it's too difficult to use it for anything else. Thus, most culm grassland remained unimproved in the past, used only for grazing small numbers of cows.

Culm grassland

Changes and advances in agricultural practice, though, have made changing the character of the land far more viable. The culm grassland has gradually been lost to modern farming techniques and increased pressure upon the farming industry to deliver ever-increasing yields, resulting in overgrazing and the draining of the Culm fields.

About 92% of our Culm grassland has vanished forever in the last 100 years, with 48% vanishing between 1984 and 1991 alone. There are now only about 4000 acres left. Fortunately, before all was lost, attempts were made to preserve it, notably by Devon Wildlife Trust, Butterfly Conservation and Natural England, all of whom have spearheaded conservation projects and continue to fight hard to preserve it.

I look outside, and it's still tipping down. Rosie is flat out, draped upside down across her cushion and snoring like a small furry engine.

I come to the conclusion that, armed with my newfound knowledge of culm and chert, it's time to stop suckling on the trivia teat that is Wiki and try to gain some knowledge from an actual, live person. I decide to try and speak to the manager of the culm grassland at Volehouse Moor.

At the Devon Wildlife Trust office, a very nice lady answers the phone and gives me the number of Steve, who looks after Volehouse.

As I listen to Steve's phone ringing. I realise that I haven't really thought this through, and that I should have prepared all kinds of interesting and insightful questions for him. All I can think of at the moment is 'why don't the cow's hooves squash all the Marsh fritillary larvae'?

As it happens, I needn't have worried. Steve is a softly spoken chap who is very easy to talk to. I forget that I forgot to prepare any questions, and we just chat away.

My opening gambit is to ask him how long he's looked after Volehouse. He tells me that he's been involved in the management of Volehouse and other nearby reserves since the early nineties. I tell him about my Marsh Fritillary count and he says that he did his own count a couple of days later. We compare totals- he had fortysomething in 45 minutes and I had 87 in 70 minutes so it's reasonably consistent.

Back in 1998/9, he says,when he and his colleague reserve manager Gary Pilkington did a count, they found just 2 butterflies. I find this extraordinary, and a testament to the success of their conservation plan. Steve is obviously quietly proud of the figures, but is at pains to point out that as a result of Volehouse being a nature reserve, he has the luxury of being able to manage the land as he wishes, without having to deliver a profit on it.

Coming from a farming family himself, he understands the pressures on farmers and is of the opinion that the shift towards larger 'superfarms' can be a positive thing for conservation because they are more likely to be able to spare pockets of land to put aside for more wildlife-friendly use.
With less land, the need to use every square metre increases. Viewed through this lens, Culm doesn't really pull its weight, so it's just as well that there are organisations willing to fight its corner.

I ask how a typical year managing Volehouse would work and Steve maps out his annual routine for me. He says that there are really two pillars to managing culm- grazing and swaling (burning)

The grazing is essential to prevent the build up of dead leaf litter, which smothers new plant growth. The Marsh fritillary, in particular, depends on high concentrations of devils-bit scabious for its larvae. This is one of the plants that can be smothered if grazing doesn't happen.

Without good management, many plants would be lost

Overgrazing, however, is as bad as undergrazing, says Steve, since the cows will eat their way through too much of the plant life. He makes the point that each area needs to be managed on its own merits, and it is this approach which he believes has led to the spectacular resurgence of the Marsh fritillary at Volehouse. He says that he puts his cattle on in mid June "whichever week has the 18th in it" although they're a bit early this year due to the mild winter and early spring.

The main thing, he says, is to only put a small number on, and not to introduce them until after the wildflowers have set seed. As a farmer, he'd want more cattle on the land and to put them on earlier, but cows tend to selectively graze out the orchids. Once again, he appreciates having the luxury of being able to manage the land for the wildlife, not in spite of it. He'll take the cattle off again in autumn.

Grazing at Volehouse is delayed until after the wildflowers have set seed

Swaling (controlled burning) is also vital to the survival of species on the culm grassland. It's another method of removing dead leaf litter and 'thatch' (the dead grass that sits on top of the tussocks) and the resultant bare earth is a perfect germination ground for seedlings. It's also the best way to stop the encroachment of scrub. Willow in particular can quickly take over a site if left unchecked. Ideally, culm grassland works best for wildlife with about 10% scrub cover.

Obviously, you can't just go around setting light to entire reserves willy-nilly and the swaling process is carefully managed by Steve, using a  3 year cyclical system of compartments, some fields being burned annually and half of the other fields being swaled every other year. The fields are cut in the winter and burned in February or March, which Steve says works better as the cut grass is more desiccated by then. Cutting cyclically ensures that there are always a variety of climates to suit the broadest range of wildlife. The meadows aren't swaled at all, relying purely on grazing to keep the thatch and scrub at bay.

Scorpion fly (Panorpa communis) One of the many insects thriving in the microhabitats of Volehouse

I point out to Steve that the increase in the number of Marsh fritillary at Volehouse is in direct contradiction to the European-wide trend as one of the butterflies in most serious decline. Does he manage the reserve purely for the fritillaries, as the star species at Volehouse?

Marsh fritillaries on well managed Culm (and unsquashed by cattle)

He pauses, considering. 'I wouldn't say I manage it for them', he says, 'but I do manage it with them in mind'. I ask if he believes that the phasing out of traditional methods of farm management like swaling have led to this decline in numbers. He puts a different, more positive spin on his answer, saying that he believes the numbers of aurinia on his reserves have increased so dramatically because he is free to manage the land in a fashion  that optimises conditions for them.

Our conversation is coming to a natural close, and we arrange for me to accompany him to Volehouse in the autumn to help him count the larval webs of the fritillaries after the cattle are taken off.

And it's then that I seize the chance to ask my big question.

'So, Steve' I say 'How come the larval webs don't get trodden on by the cows'?

He considers.

"I expect they do'. he replies. 'But not all of them. Otherwise there wouldn't be any fritillaries, would there'?

I can't really think of a response to logic like that, so I thank him and end our chat.

I've learned a lot about culm this morning.

It's still bloody raining, though.

Devon Wildlife Trust, North Devon Nature improvement area website
Butterfly Conservation 'Reconnecting the culm' leaflet
JNCC defra SAC site
Devon county council- 'Rhos pasture'

Many thanks to Steve Threlkeld at DWT

No comments:

Post a Comment