H21a

This year I have been busy doing a big upland National Vegetetion Classification (NVC) survey on a site near where I live, covering about 3,000ha. Its been really hard work doing such a large survey by myself, but at last, I've nearly finished it!

My favourite habitat on the site is labelled as 'H21a' in the NVC. This is a habitat that is easy to recognise - heather and/or other dwarf shrubs, with Sphagnum beneath and no hare's-tail cottongrass. Around here, it usually occurs on steep (c. 45 degrees) north-facing slopes.


This is a very nice example of the habitat on a very steep (>50 degrees) slope. As the site is right on the north edge of the Pennines, there are lots of steep north-facing slopes. But you find it throughout the North Pennines, particularly in narrow strips along the north side of east to west stream valleys.


Here is a close-up showing some red Sphagnum in amongst the dwarf shrubs. You can get 4 red Sphagnum species from Section Acutifolia in this habitat - capillifolium, russowii, subnitens and quinquefarium. This is more or less the only habitat that S. quinquefarium grows in around here.

I suspect that this habitat is often overlooked in the Pennines for several reasons: it often occurs in strips of habitat that are too narrow to map; it occurs on steep slopes that are more difficult to walk along than the more gentle slopes on the top, which are usually covered by blanket bog; it looks superficially similar to blanket bog, just lacking any hare's-tail cottongrass; and all habitats with prominent bryophytes are overlooked and misunderstood, as most surveyors can't identify any bryophytes.

The shots aove show a very open sward of dwarf shrubs, but more usually there is a thick sward of dense heather with patches of Sphagnum here and there. Sometimes (on grazed sites) you get a lower sward with bare patches. It is always worth looking closely at these areas as here you often find locally or regionally uncommon liverworts. Recently, I have found Barbilophozia atlantica, Kurzia trichoclados and Lophozia incisa in patches of this habitat.

In the north and west of Scotland, whole hillsides can be covered with this habitat and the best spots have H21b, which is a version of the habitat that is much richer in liverworts. Not only are liverworts abundant in H21b, but there are usually rare oceanic species included. This is what bryologists refer to as the 'Northern hepatic mat'. Along with atlantic temperate rain forest, H21b is probably one of the most special habitats in Britain as there is more of it here than anywhere else in the world. In the North Pennines. although we get some interesting liverworts in H21a, it would be stretching it too far to refer to this as a 'hepatic mat', as there are usually only small patches of liverworts in our examples.

John