The Heavy-Metal Grasslands of Snowdonia

Photo from The Wildlife Trust’s websitehttps://www.wildlifetrusts.org/habitats/grassland/calaminarian-grassland

Dear Readers, I was reading through my British Wildlife magazine this month when I came across a type of habitat that I’d never heard of before – calaminarian grasslands. They are named after the violet Viola calaminaria, which grows on rocks which are rich in zinc, or calamine (yes, the same stuff that we slap onto our sunburn).  The violet grows only in mainland Europe, but the habitat has retained the name. Calaminarian grassland thrives where there are metal-rich rocks and contamination – in the Snowdonia region (and particularly in the Gwydyr Forest Mines which the article, by Caroline Bateson, refers to) this dates back to small-scale mining of lead, zinc and silver which started in Roman times and continued, more or less intensively, right up to 1960. Until the First World War, the area would also have been intensively grazed by sheep, which would have helped to preserve the habitat, described by Bateson as a ‘fabulous wild land of moor and bog, with pockets of deciduous woodland’. After World War I, the area was planted with conifers to ensure that the UK would be self-sufficient in timber. The small amounts of calaminarian grassland that survive are considered to be endangered in the European Red List of habitats.

Photo Four by Gilles San Martin, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons

Zinc Violet (Viola calaminaria) (Photo Four)

Calaminarian grassland is so special because the plants that survive there are largely metallophytes – plants that thrive on high levels of metal in the soil. They are often not large or showy, but they are often very rare. One particular plant is known as Lead Moss (Ditrichum plumbicola), and the Gwydyr Forest Mines are described as ‘the single greatest area globally’ for this plant, which is found only in the UK and Germany. In the photo below, it’s growing on the spoil from a lead mine. Bateson notes that it is ‘perhaps the least visibly engaging’ of the Gwydyr species, as it disappears in the drier months of the year, and can only be identified to species level with a hand lens. This makes it a difficult conservation ‘sell’ to the general public, unlike, say, an orchid or a particularly resplendent butterfly.

Photo One by Des_Callaghan, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Lead Moss (Ditrichum plumbicola) (Photo One)

Lead Moss positively thrives on the toxic soil of these sites, and therein hangs a conundrum. As the toxicity gets less (through rainfall and natural succession), the moss is outcompeted, and the pine needles dropping from the conifer forest don’t help.

Another plant that is an ‘obligate metallophyte’ is Alpine Pennycress (Noccaea caerulescens).  It actually needs the toxic substrate of lead, zinc and silver mines to survive, and will not grow anywhere else. Bateson says that it is very abundant at the Gwydyr site, although it is nationally scarce. It is what’s known as a hyperaccumulator, which means that it can pick up extremely high levels of heavy metals and store them in its leaves and cell walls without being poisoned. It could possibly be used to detoxify contaminated sites.

Photo Two by Hugues Tinguy, CC BY-SA 2.0 FR <https://creativecommons.org/licenses/by-sa/2.0/fr/deed.en>, via Wikimedia Commons

Alpine Pennycress (Noccaea carulescens) (Photo Two)

Other plants found at Gwydyr include the rare Forked Spleenwort (Asplenium septentrionale) and a genetically adapted race of Sea Campion which, as the name suggests, is usually a coastal plant. It has evolved to tolerate soils with high levels of toxicity. There are also some very rare lichens which are also heavy-metal lovers, and a recent survey found two species of lichen that were new to Britain, and two that were new to science.

Forked spleenwort (Asplenium septentrionale) (Photo Three)

The question is, however, how to preserve this unique grassland, and indeed should we even be trying? The habitat arose out of environmental abuse and exploitation, and yet nature has made the best of it. The question is further complicated by the variety of tiny niche habitats within Gwydyr. Work that has been done so far has involved removing the conifers and scrub, a delicate process because the mosses and small plants that are the subject of the conservation effort won’t benefit from being trampled – cut trees have to be carried, rather than dragged, off site for example. In Cornwall, an attempt to conserve another metallophyte involved scraping off the top soil to reveal more toxic material. Unfortunately, the areas were quickly colonised by other vegetation, and it seems to be important to reveal pockets of toxic soil rather than large areas that allow the ‘big guns’ to move in.

Grazing used to be a key feature of these grasslands, but even this is problematic. Too many sheep will change the habitat by trampling and dunging, and of course the toxicity levels have to be considered with regard to the welfare of the animals. Other management possibilities include hand-strimming (which is particularly good in preserving the right conditions for Alpine Pennycress) and hand-weeding, and Bateson makes an excellent point here. I quote her below:

“Ideally, I should like the grasslands managed so that their unique biodiversity has the best chance of surviving into the future. Yet there are legitimate reasons to question the justification for these management methods, particularly in terms of the use of heavy machinery and power tools which have a high carbon footprint. Instead of looking backwards and trying to implement management techniques that are costly and unsustainable, perhaps a novel approach is needed. Would it be possible to bring back labour-intensive land management to enable green jobs, address health and wellbeing, encourage a greener economy and aid nature conservation simultaneously?” (Bateson, British Wildlife February 2022 pg 252)

What an excellent question, and one that it’s well worth pondering. Coincidentally, I am reading a book by Cal Flynn called ‘Islands of Abandonment’ which discusses a range of human-created landscapes (including, incidentally, the calaminarian grasslands) and how they can so often act as refuges for biodiversity. We need as a species to move away from only conserving what is beautiful in our eyes, and towards a more pragmatic assessment of where species are surviving. Brownfield sites are often richer in insect species than artificial meadows, although the latter might be prettier. We need to retrain our eyes to see what’s really there.

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