Thrislington National Nature Reserve is located approximately 10km south of Durham City and lies on the western edge of the Durham Magnesian Limestone Plateau.
This plateau itself rises eastwards from the City of Durham reaching to almost 200 meters in height, forming cliffs along the North Sea coast of County Durham. This special type of limestone stretches northwards almost reaching the Tyne estuary and southwards, just crossing the border in to Hartlepool.
Thrislington National Nature Reserve
The story begins 290 million years ago when the UK was much further south, somewhere just above the equator, when most of what is now northern Europe was covered by a warm shallow tropical sea – the Zechstein Sea. From time to time this sea would dry up, in what was then, a warm arid environment. This cyclic series of drying up caused minerals to crystallise forming, amongst others, the Dolomites, otherwise known as Magnesian Limestone.
This special grassland is typically found on thin, well-drained, lime-rich soils and lies on a climatic divide intermediate between the chalks of southern England and the more northerly carboniferous limestones; nationally it only occurs in a narrow band stretching from Nottinghamshire through to the east Durham plateau.
This mineral-rich bedrock became the basis of exploitation for industry and agriculture through much of the 19 and 20th Century. Here at Thrislington it has been preserved as a National Nature Reserve to help protect the flora and fauna that make this special jewel their home.
Today it supports the largest area of Primary Magnesian Grassland in the UK, having survived afforestation during late 19th Century, scrub encroachment in the 1960’s and quarrying in the 1980’s.
During the early 1990’s part of the site is was subject to an ambitious conservation project, which saw an area of primary grassland, which would have otherwise been lost to industry, transplanted onto adjacent land that is now part of the NNR. This process involved a partnership between industry and conservationists in which large slabs of turf were successfully transplanted, like a jig-saw, to save and preserve for future generations.
Few areas of original Magnesian Limestone grassland remain today, those that do, such as Thrislington NNR, are some of the most species-rich grasslands in Europe and the site is widely recognised as one of the most important stands of this primary Magnesian Limestone grassland still found in Britain today. Here it is protected by SSSI (Site of Special Scientific Interest), SAC (Special Area of Conservation) and NNR (National Nature Reserve) status.
Orchids on limestone grassland. Left: Greater butterfly-orchid. Right: Common spotted orchid.
Like other unimproved calcareous grasslands, Thrislington is species-rich and is of significant botanical interest, containing the largest of the few surviving stands of Sesleria albicans – Scabiosa columbaria grassland (known as CG8). This form of calcareous grassland is restricted globally to the Magnesian (Permian) Limestone of north east England and unfortunately it’s found mainly as small scattered stands covering less than 200 ha nationally. More than 235 species of flowers, grasses and sedges have been recorded including eleven species of orchid. There’s also significant invertebrate interest with one Red Data Book species, the least minor moth Photedes captiuncula, 23 other `notable' species and 12 species of local significance, including the Northern brown argus butterfly (Aricia artaxerxes salmacis) and glow-worm (Lampyris noctiluca).
Left: Northern brown argus. Right: Common blue