Acid grassland

Although the geology of Wharfedale suggests that acid soils will be found in the Millstone Grit areas, in fact this is not entirely true. The Yoredale series includes shales and sandstones, with more neutral soils existing as a transition between them. The glacial deposits include stony clay deposits which tend to be very heavy, resulting in poor drainage, low fertility and quite acidic conditions. Even on limestone soils, the wet conditions lead to a leaching-out of calcium and other important minerals and many farmers have to add lime to fields in limestone districts.

The result of these processes is the development of infertile, acidic conditions which favour communities such as acidic grasslands, bogs and heaths. Over time grazing has eliminated the ericaceous species from many of the heathland areas and large areas of grassland are the result. In the Yorkshire Dales National Park as a whole, acidic grasslands make up about a quarter of the land use.

The commoner plants in these grasslands include mat-grass, common bent, heath bedstraw, sheep’s fescue and tormentil. Rather less frequent are bilberry, sheep’s sorrel, sweet vernal-grass and wavy hair-grass. Sometimes devil’s-bit scabious, heath milkwort, spotted and more uncommon orchids, mountain pansy and fir clubmoss are found.

The high fells have a severe climate and the grassland is species-poor. Sheep’s fescue tends to be replaced by its montane equivalent viviparous fescue and there are small amounts of Cladonia lichens, ericoids and, rarely, fir clubmoss or the montane stiff sedge.

The acid grassland around Ilkley Moor is dominated by mat-grass and wavy hair-grass. Wet slopes have purple moor grass and the wettest areas support heath rush. This kind of acid grassland, and the semi-improved areas around the edges of moors, are favoured by curlew, with lapwing and, in the wettest areas, snipe and redshank. The twite in our area are an isolated southern out-post of the race pipilans that occurs only in Scandinavia and the British Isles and is itself isolated from the rest of the world population in the mountains of Central Asia. Once found on Ilkley Moor, they can now be seen, with luck, around Grimwith reservoir.

Besides woodland, Otley Chevin also contains extensive areas of acid grassland, with occasional patches of gorse scrub. These areas are home to birds such as the stonechat and butterflies such as the common blue and green hairstreak.

Severe grazing pressures have produced grassland with bracken, mat grass and heath bedstraw on Barden Moor and Blubberhouses Moor. Wet patches are dominated by heath rush and here heath bedstraw is likely to be the only common herb. Heath rush is confined almost entirely to western Europe where it is most frequent in wet, oceanic districts, and it has an important stronghold in Britain. Where bogs have been degraded by over-grazing, cotton-grass may be found. The reservoirs at Barden and Grimwith provide feeding areas for moorland nesting birds like dunlin as well as nesting habitat for common sandpiper and grey wagtail.

In the Malham-Arncliffe area the acid grassland will typically have mat-grass, wavy hair-grass, heath bedstraw and tormentil. Some heather and bilberry may also be found. Across the valley at Conistone Old Pasture areas with deeper soils support grassland with mat-grass, tufted hair-grass and, of course, heath bedstraw. There is a great deal of more neutral grassland, with wild thyme, harebell and, locally, mountain pansy, in a sward dominated by fescues and bents.

At Kettlewell Meadows there are some acid areas, with sheep's fescue dominant with common bent and red fescue. Although there are fewer herbs in these acid areas, the community is notable for the abundance of mountain pansy.

On Pen-y-ghent either mat-grass or purple moor-grass dominate the grassland and higher up this contains stiff sedge Carex bigelowii.