cliffs, bluffs, outcrops, caves and screes are a distinctive feature
of many Mendip nature reserves, especially Cheddar
Combe, Ebbor Gorge and
Draycott Sleights. Such habitats present particular challenges; they
are often sun-baked and wind-scoured, with small pockets of impoverished
soil. Screes are unstable, nutrient-poor and dry. On Mendip, both
habitats support very distinctive vegetation communities, which include
a number of uncommon plants.
Limestone cliffs offer plants some protection from grazing animals
and human attention. Whilst the now rare Cheddar pink was once widely
distributed throughout Cheddar Gorge, today it is frequent only on
high, inaccessible crags where it is relatively safe from collectors.
This plant, like some others that are characteristic of cliff habitats
on Mendip, needs open, sunny situations and cannot tolerate much
competition from other plants. Other notable cliff-dwellers include
slender bedstraw, lesser meadow-rue and spring cinquefoil and, in
Cheddar Gorge, two endemic whitebeams.
Rue-leaved saxifrage Saxifraga tridactylites, a common
inhabitant of rocky crags. Photo. Sharon Pilkington.
Open, sunny screes tend to support vegetation that is dominated by
lime-loving perennial species and open scrub. Many screes are home
to limestone fern, a nationally scarce fern rare in southern England,
and false oat-grass. Whilst these species need an open, sunny situation,
many other plants found on screes are more commonly associated with
woodlands. Herb Robert, wood sage, wall lettuce and dog's-mercury
are all common. Mats of calcicolous (lime-loving) mosses play an
important role in stabilising rock talus, and shady microclimates
provided by larger rock fragments or crevices support a distinctive
assemblage of small ferns, including maidenhair spleenwort, wall
rue and rustyback.
Many natural caves have developed in the limestone bedrock, and their
chambers, rifts and passages are a very important habitat for nationally
rare greater and lesser horseshoe bats,
especially during winter when they frequently hibernate underground,
where the air temperature tends to remain stable.