I thought lockdown was going to provide the opportunity for lots more botanising and writing but somehow that doesn’t seem to have worked out. Marking and Zoom meetings to rearrange teaching commitments have taken their toll though, to be fair, I’ve also spent far more time than usual in the allotment this spring and made more use in the kitchen of the last of the leeks and spring cabbage and the new season’s rhubarb than I sometimes do. Not much has happened in terms of my flora chapter for the book on the natural history of Upper Weardale, though hopefully that is about to change.
Now that the restrictions on non-essential travel have lifted, we can travel back to Weardale for a little more exploring with clear consciences and a tip off about a Bird’s-nest orchid is enough to persuade us that Stanhope Dene is the place to visit. Stanhope burn flows off the moorland to the north and down through the wooded dene to join the River Wear at Stanhope. The last Saturday in May is a glorious day and plenty of others are heading up the dale but once we park and we head off on foot towards Ashes Quarry, we meet only a few other walkers. We used to take Durham undergraduates here to look at the difference between the vegetation on the limestone spoil heaps around the quarry and the moorland vegetation on the more acidic sandstone-based soils at the top of the hill. Always an interesting experience in October, as many students come from further south and didn’t really believe us how much lower the temperature would be at the top of a north Pennine hill than in Durham! From the latter half of the 19th Century, wagonloads of limestone quarried here were pulled several hundred metres up the Crawleyside incline by winding engines, before coasting down the Stanhope and Tyne railway to Consett for use as flux in the steel works.
Past Ashes quarry, the path crosses the steep Crawleyside road along the old railway route and drops down to Stanhope Burn. More by accident than design we stayed on the parallel path a little higher up the hill, passing through more old quarries before dropping to the track which follows the burn up to the remains of Stanhopeburn lead mine workings. You can still see the tunnel flues from the smelting mill running up the fellside.
What now looks like natural mixed deciduous woodland alongside the burn was ‘laid out’ during the Durham coal strike of 1892, complete with seating, rustic bridges and a bandstand. The woodland floor on the east side of the burn is carpeted with Alchemilla – A. xanthochlora, I think,as the upper sides of its leaves are hairless. I spot my first Marsh orchids of the year by one of the old quarry ponds near the path.
Above the mine workings we venture a short way up the burn into more open heathland, with plenty of Heath bedstraw and Tormentil amongst the heather. Crossing the burn, we can see just how low the water levels are after the sunniest, driest May on record in this part of the world – the limestone pavement is just about that! Climbing the hill on the far side of the burn we hear a cuckoo, then see it fly away as we get too close; they are distinctive birds in flight, but much more often heard than seen. I wonder what bird species it parasitises up here? Most of the birds we see around here are ground-nesting species; larks, lapwings, oystercatchers and curlews, though also many ‘Little Brown Jobs’ I’m not confident about.
We loop round past the farms at the top of the dene and drop back down to Stanhope burn, following a completely dry tributary down through another old quarry. Here the vegetation is classic limestone flora – Dog violets, more Alchemillas, Pignuts, Bitter vetchling and beautiful Wood crane’s-bill.
However the real star of the show, though another species which likes limestone soils, doesn’t appear until we are back in the shady beech and oak woodland which clothes the dene proper. Bird’s-nest orchid, named for its mass of short, thick roots,is a true botanist’s plant, lacking the showiness and bright colours of most of our native orchids but exciting to those, like me, who’ve never seen one before. It is not common in northern parts of the country. The single spike we find is only 15 cm or so tall, pale brown in colour and difficult to photograph because of its indistinct features.
The pallid colour reflects the fact that this is a parasitic orchid, almost devoid of chlorophyll and so unable to photosythesise for itself. Many orchids rely on a fungal, mycorrhizal partner for germination but Bird’s-nest orchids take things a step further, relying entirely on a specific Sebacina sp. fungal partner for carbohydrate supply throughout their life. The fungus itself, of course, relies on its green plant partner (usually a Beech tree) to supply carbohydrates in exchange for the mineral nutrients and water the fungus helps it obtain. In effect, the orchid is parasitising the trees around it, using the fungus to connect it. Bird’s-nest orchid is so dependent on fungi that its ability to produce flower spikes at all is often limited by weather-dependent fungal growth, so we were truly lucky to find this at the end of such a dry month.
The mycorrhizal network which supports woodlands like that at Stanhope dene remain mostly out of sight beneath our feet as we walk back towards the town but we do see some spectacular ‘Chicken of the Woods’ Laetiporus sulphureus on the bark of one oak tree – something or someone will surely make a good meal of it!