The geology of a certain area of County Durham has created a unique habitat that promotes an enviably high biodiversity – the magnesian limestone grasslands.
Climbing over a stile into Littlewood Local Nature Reserve, in the heart of County Durham, I find the first field knee-high in rough meadow and sweet vernal grasses, meadow fescue and cock’s-foot, and wildflowers: woundwort, bird’s-foot trefoil, knapweed, speedwell, herb robert, hoary plantain, red and white clover – a botanical smörgasbord.
A lot of time and trouble has gone into removing the rich remnants of agricultural production from this small, mixed patch – bounded by a main road and the scars of three large quarries – to restore a habitat in which wildflowers and all their associated invertebrates and birds flourish.
It’s June and the myriad shapes of the grasses and the brilliant natural colours are dazzling. Further assaulting the senses, there’s the smell of fresh herbage warming in the sun, the dancing movement of butterflies, the buzz of bees, and the rapid chip-chip of a linnet from the hawthorn surrounding the meadow.
“The hawthorn is good for bird life,” says Adam Dixon, countryside ranger for Durham County Council, who oversees the reserve. “But it encroaches on the grassland, so we have to keep it in check.” The same
goes for rosebay willowherb, which he takes the tops off as we encounter the plants on our walk. This will help to prevent the flowers setting seed and spreading, he says. This hugely successful plant was given the nickname of fireweed because of the speed it colonised bomb sites in World War II. Given the chance, it would engulf the more delicate species in the grassland, so it cannot be left alone.
The good, the bad and the ugly
Volunteers help with clearing willowherb and the courser grasses through the growing season and cattle graze in the winter months to churn up the ground and keep down the less desirable vegetation.
“We occasionally spread yellow rattle seeds, to help suppress the ranker grasses,” says Adam. “Yellow rattle parasitises those grasses, which kills them and opens up the grasslands to allow wildflowers to flourish.” A particular problem in the Durham area has been upright brome, a grass that has been steadily spreading northwards from its southern and middle England heartland. If this takes hold, it can dominate a meadow; its dense tussocks and leaf litter inhibiting more delicate plants from taking root, thus stifling biodiversity. Regular mowing and grazing is necessary to keep this invader from taking over.
The meadow was arable farmland until 2005 when Durham County Council took it over. It sits over the site of East Hetton Colliery that closed in the early 1980s, and of which little evidence remains, apart from the covered-over spoil heap, now crisscrossed by tracks and planted with conifer woodland for commercial use. The only
other sign that this was once a thriving coal mine, employing about 1,500 men at its height in 1896, is the occasional concrete drainage conduit that runs through the site.
The terrain in the area has been shaped by its unique geological composition. This part of central County Durham, from as far west as Bishop Auckland in the south and Houghton-le-Spring in the north, and stretching to the east coast between South Shields and Hartlepool, is a roughly triangular magnesian limestone plateau. Magnesian limestone is one of a group of dolomite limestones that run in a line, between 2–8km wide and about 200km long, from Nottingham to Sunderland.
This limestone is unique in the UK and dates back to the late Permian Age, 240 to 270 million years ago, when the area was covered in a large, land-locked stretch of fresh water called the Zechstein Sea. This was a time before the world’s continents had drifted apart and the Zechstein was bounded by narrow strips of land outside of which was a much larger saline sea. The strips of land were constantly breached by incursions from the outer sea, introducing salt to the fresh water that gradually accumulated to make the water hypersaline, in the way the Dead Sea has formed today.
Through time, and with a changing climate, the water evaporated and mineralrich deposits formed the limestone layers, overlaying sand and the seams of gas and coal that sustained the lives of Durham and Yorkshire miners for generations. Nowadays, the collieries are gone, though the limestone is still quarried for aggregates.
In 2007, it was recognised that the magnesian limestone promoted a type of grassland with a huge diversity of flora and fauna, and that it should be safeguarded. The Limestone Landscapes Partnership was formed between Durham County Council, Natural England, Historic England and a raft of local councils, wildlife and outdoor organisations. It operated between 2007 and 2016 to promote and preserve the natural resources of the area, a legacy that continues. Its work included returning sites such as Littlewood Local Nature Reserve to the biodiverse richness that existed before modern agriculture made use of the land.
The heritage of decades of farming at Littlewood had left the ground full of fertiliser and pesticides and it has required careful management to return it to a native meadow providing habitat for a range of animals, including ground-nesting birds, such as grey partridge.
“Cattle, particularly Highland cattle, and Exmoor ponies are the preferred species to graze the meadow between October and April,” says Adam. “They are less picky than other grazers in their habits. Highlands will clatter through everything, even gorse!
“Two years without grazing and you lose the sward height, the rank stuff takes over and you have lost the biodiversity. As it is, this Site of Special Scientific Interest meadow is between two others and is part of a scheme to build up a wildlife corridor all the way to the coastal grassland sites.”
The management of the land is highlighted in the second field beyond a thick hawthorn hedge. This meadow is in a narrow valley, with the hedge on one side and mixed deciduous trees and bushes on the other. “We leave at least 10 per cent of this meadow uncut, on rotation,” says Adam, “in order to provide shelter for smaller mammals and amphibians.”
He points out how the wildflowers and grasses grow well in most of the field, but in the bottom quarter nettles and rosebay willowherb grow to waist height and to the exclusion of the more delicate grasses. “We hand mow the meadow,” he says. “But the way in is too narrow to get in a trailer big enough to remove the cuttings in any quantity. So we’re forced to dump them at the bottom of the field. The cuttings rot down, but they leave the soil nutrient-rich, which is great for nettles but not the kind of plants we want, that thrive on nutrient-poor ground.”
The wildflower meadows are one aspect of the regeneration of the reserve. The second is the area where Adam is experimenting with scraping off the farmed ground, leaving rocky yellow magnesian limestone only thinly covered in soil. “The southwest-facing land is sheltered,” he says. “This brings the heat in and we have introduced common rock-rose and various other native species as plug plants. We’re looking for that balance that will create a mosaic of habitats that are good for a wide range of species.”
In terms of invertebrate life, he adds: “The 5–10cm height of the sward on this patch is good for the northern brown argus butterfly, a nationally rare species known locally as the Durham argus, that lays its eggs on the common rock-rose, which provides food for its caterpillars. Even lower growth suits the dingy skipper butterfly.”
Altogether, this small reserve hosts more than 18 species of butterfly, burnet and chalk carpet moths, at least four species of bumblebee and many other invertebrates. Bird life includes skylarks, willow tits, little owls and grey partridge, the latter thriving here in contrast to national declines. The mammal population features brown hares, field voles, weasels and, less happily, rabbits.
Rabbit versus orchid
One of the reserve’s pride-and-joys is the dark-red helleborine, a rare wild orchid found in only a few areas of Britain. The limey nutrient-poor scrapes at Littlewood suit the flower, but sadly the flower very much suits the rabbits, as a delicious nibble. Adam admits that it’s sometimes a war of attrition to protect the helleborines from an overpopulation of rabbits.
The rock-roses that are now growing extensively on the newer exposed limestone areas were spread from seed taken from areas of the site where they occur naturally. One of these places is beside the concrete
Magnesian limestone promotes a type of grassland with a huge diversity of flora and fauna.
culverts that took water round the spoil heap to the mine, which did not see the soil enriched like the site’s agricultural sections.
Another rare ground-hugging plant, the basil thyme, also thrived near the culverts, benefitting from the lime-rich environment and lack of herbicides. Littlewood is one of only four colonies of basil thyme that still exist in County Durham. Classed as Vulnerable, this member of the dead-nettle family is listed as a plant “of principle importance for the purpose of conserving biodiversity” in the 2006 Natural Environment and Rural Communities Act.
Littlewood encapsulates the beauty and biodiversity of Durham’s magnesian limestone grasslands – precious habitats clawed back from industrialisation and intensive agriculture to showcase what can be achieved with careful management. A network of sites that includes Thrislington Plantation National Nature Reserve (NNR), Castle Eden Dene NNR, Cassop Vale NNR and Blackhall Rocks, among others, offers a step back in time and a step forward into the future for our native wildlife.
Clockwise from above: rock-rose, on which northern brown argus butterflies lay their eggs; Adam Dixon, showing the varying sward heights at Littlewood; East Hetton colliery and slag heap in 1983; the rocky nutrientpoor landscape suits flower-rich grasslands; a burnet moth feeding on knapweed.
Above: wild orchids thrive at Thrislington. Below: nettles indicate nutrientfilled soil that inhibits biodiversity.
A wide range of native plants are good for invertebrates and birds such as skylarks.