Wild thyme, rock rose andstonecrop on limestone
scree in Trollers Gill.
Photogragh by Roger Henson.
The vegetation of cliff habitats is influenced by the slope, stability and aspect of the cliff face, the degree of shelter afforded against extremes of climate, and the nature of the rock.
Steep, unstable and exposed cliff faces support a range of poorly competitive, pioneer species, such as common whitlowgrass, hairy rock-cress and thale cress, as well as those intolerant of grazing. Many plant species can also be regarded as ‘cliff specialists’ as they have certain adaptations for withstanding the sometimes harsh environment of cliff habitats, for example, biting stonecrop, which withstands drought conditions by storing water in specially adapted succulent leaves. In the Yorkshire Dales another specialist of limestone cliff ledges is the rare winter annual hutchinsia. Scree slopes below unstable cliffs also have their special plants including the prickly sedge which is critically endangered in the UK.
In sheltered positions on stable rock, ferns like the green spleenwort, the evolutionary very old lesser clubmoss and a range of more robust flowering plants can develop. These include marjoram and small scabious, which are also found in limestone grasslands. These plants proliferate in these conditions because they are isolated from grazing animals. Likewise, there are some other species which are intolerant of grazing and competition and are largely restricted to stable rock faces, such as the alpine cinquefoil and the greater knapweed. Tree species which are successful at colonising cliff faces include the juniper, the rowan and its relative the scarce rock whitebeam.
Where flushed permanently wet cliff faces occur in parts of Swaledale and Wensleydale, the plant species marsh hawk’s-beard, Pyrenean scurvygrass, mossy saxifrage and stone bramble can be found.
To find out more about plant species of limestone cliffs and scree in the Yorkshire Dales please follow the links provided.
