Limestone pavements

Description (English)

Regular blocks of limestone known as "clints" with loose flags separated by a network of vertical fissures known as "grykes" or "shattered pavements", containing more loose limestone rubble. The rock surface is almost devoid of overlying soils (considerably less than 50% cover) except for some patches of shallow skeletal or loessic soils, although more extensive areas of deeper soil occasionally occur; sometimes there is encroachment of peat. This morphology offers a variety of microclimates allowing the establishment of complex vegetation consisting of a mosaic of different communities. The fissures provide a cold humid microclimate where shade-tolerant vascular plants such as Geranium robertianum and Ceterach officinale occur, as well as formations of herbaceous species typical of calcareous woodland; the small pockets of soil are occupied by communities of Mesobromion (e.g. Seslerio-Mesobromenion); heath and scrub also occur (e.g. Corylo-Fraxinetum). Apart from the species rich areas of scrub (generally Prunetalia spinosae), the ecosystem is maintained by grazing in some regions; this, combined with severe winds, means that isolated shrubs can only survive in prostrate growth form (e.g. Dryas octopetala); at ungrazed sites, marginal areas of Geranium sanguineum occur.
In Sweden, limestone blocks are larger and cracks are smaller. The species composition reflects a more continental, dryer and cooler climate. The pavements are mostly exposed with scattered cushions of bryophytes, more seldom covered by a thin layer of soil. The surface is covered by Sedum album, Cerastium pumilum, Cerastium semidecandrum, lichens (Aspicilia calcarea, Thamnolia vermicularis, Verrucaria nigrescens) and bryophytes (Tortella tortuosa, Grimmia pulvinata). The vegetation in the cracks contains Gymnocarpium robertianum, Asplenium ruta-muraria, Asplenium trichomanes ssp. quadrivalens and, occasionally, bushes of Prunus spinosa, Fraxinus excelsior, Cotoneaster spp., Rosa spp.
Some sites in Ireland host an open Taxus-Juniperus scrub of major interest; certain arctic alpine species such as Gentiana verna and Dryas octopetala are characteristic and in The Burren, these species occur with Atlantic-Mediterranean species such as Neotinea maculata.