Lockdown challenge 2021 – Cassop Vale National Nature Reserve

I seemed to miss the opportunities for reflection which the end of 2020 should have offered and find myself at the beginning of 2021 in another national lockdown, with few options for exploring any distance from home.  2020 was the first time in many years that all my plant hunting has been done in the UK and there were, of course, some advantages in spending more time outdoors close to home.  Working on the botanical chapter of Durham Wildlife Trust’s new Natural History of Weardale encouraged us to explore parts of Weardale we hadn’t visited before, including Slitt Wood and Stanhope Dene, where I saw my first Bird’s nest orchid. 

I loved revisiting my monthly trips to Raisby Hill in 2019 for a YouTube talk for ERIC North East, the Environmental Records Centre based at the Great North Museum in Newcastle – seeing the reserve change through the seasons was a timely reminder that things will not be like this forever. It seems like a good time to repeat this exercise on a different local reserve as we are largely limited to visiting places we can reach on foot, or by bike, from home.  By mid January we’d already had two lockdown walks to Cassop Vale NNR, above us on the Magnesian limestone escarpment, so that’s going to be my choice for 2021.  Neither of the first two trips was much good for plant hunting, as a result of the snow!

Cassop Vale NNR

Last weekend I decided to go back for a proper look around to see what I could find though, to my surprise, there was still snow on the ground in shady, north facing areas and the pond was sufficiently frozen for snow to be lying on it too.

It turns out to be less than an hour’s walk to Cassop Vale from our house, straight up and over the escarpment past Quarrington Hill – eminently do-able as a regular walk. We’ve normally walked up the path along the old waggonway through the valley to the pond and haven’t really explored the rest of the reserve, so my aim was to work out which parts are accessible to the public and where to find the Magnesian limestone grassland, which is one of its highlights.  When Cassop was designated a Site of Special Scientific Interest in 1985, this was described as ‘one of the more extensive examples’ of Magnesian limestone grassland, though I fear it may have been encroached on and degenerated since then. 

Though the SSSI designation is linked to the limestone flora, the site is a rich mosaic of grassland, woodland, scrub and wetland habitats, partly as a result of its mining heritage.  I tried to walk the bounds of the site on Saturday but the slopes in the northern part of the reserve are covered with impenetrable gorse, though it looks like that has been recently burned in an attempt to control it.

I wasn’t sure about access to the ground around the pond either and the problem there turned out to be rather different – the highland cattle grazing there over winter to bring rank grasses under control. They are certainly doing a good job of churning up the ground, but I’ll feel more comfortable exploring the north side of the pond once they have finished and departed to pastures new!

As a SSSI, Cassop Vale has been well studied and John Durkin, who was BSBI Recorder for County Durham at the time, produced a list of over 320 plant species found there in 2011.  These include lots of interesting and surprising finds for such a lowland site – Globe flower and Bird’s eye primrose (key to the SSSI designation), Adder’s tongue fern and Moonwort. Though some of the ‘notable species’ have not been recorded since the 1960s and 70s, Bird’s eye primrose was found there in 2007 and Globeflower when the site was last surveyed in 2011, so there is plenty to hunt for.  The other species listed in the designation is Phothedes captiuncula, the Least minor moth, which I’m frankly unlikely to find without help.  I might be more likely to spot a Durham argus butterfly, another important resident!

Phothedes captiuncula. Image Rob Petley-Jones.

I was keen to locate the Magnesian limestone grassland, which is supposed to be a mixture of primary and secondary grassland, the latter in long-abandoned quarries on the south side of the reserve. I know what treats are to be found in other, nearby, quarry sites at Bishop Middleham and Raisby Hill and saw some typical species, such as Blue moor-grass (Sesleria caerulea), in tiny local quarry sites above the valley on our walks last summer.

Blue moor-grass, Sesleria caerulea

It’s the first time I’ve made regular visits to a site with a species list so it will be fine to play ‘I-spy’ over the next twelve months!

I thought I ought to find out a little about the history of Cassop Vale and the forces, natural and anthropogenic, which have shaped it.  ‘England’s North East’ suggests the name Cassop might be derived from the Old English ‘cat’s hop’, i.e. ‘valley of the wild cats’.  However ‘Keys to the Past’ suggests a more prosaic origin from the Anglo Saxon name, Casa; so simply ‘Casa’s valley’.  Apparently the valley was one of many areas used as a hunting park by the Prince Bishops of Durham, who often seemed more interested in the physical than the spiritual realm!  As well as  local limestone quarrying, Cassop Vale Colliery operated for a short period from 1840 to the 1850s alongside the main pit at New Cassop, now simply called Cassop, at the head of the valley.  Areas of exposed spoil beside the pond add to the rich diversity of habitats on the site.

There is a local myth that the depression which now holds the pond known as Cassop Bogs was created by a WWII German plane offloading bombs at the end of a raid but, sadly, I’ve been able to find no evidence for that!  It seems more likely to be the result of mining subsidence – there are many problems linked to this in and around the villages of Cassop and Quarrington hill.  Heading west down the valley, the grassland gives way to hawthorn, elder and ash scrub, the branches festooned with tiny baubles of moss and lichens which are such a vibrant green at this time of year.

Moss and lichen gardens on elder scrub – White-tipped Bristle moss, Orthotrichum diaphanum, and yellow Xanthoria parietina.

The wooded area beyond that, through which the path down from Quarrington Hill passes, is known imaginatively as Big Wood. Parts are supposedly ancient woodland and John Durkin’s records indicate it certainly has been home to species such as Herb Paris, Paris quadrifolia, which indicate it has been there, undisturbed, for some time.  Signs of spring are there already, for those who care to look, but as we’re due to see the ‘Beast from the East’ Part 2 this coming week they may be on hold for a little while yet!

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