Compton Down

Also within

Isle of Wight County Isle Of Wight Scenic Area King Charles Way - IOW 5 Chilton Chine to Colwell Chine National Trail

Condition (Natural England)

Geology & landscape

Rock Type: Chalk

Description

Description Compton Down SSSI occupies 4.5 kilometres of the east–west chalk anticline of the Isle of Wight and includes both the south and north facing slopes and crest of the ridge. It is probably the best example in Britain of chalk grassland under maritime influence. On the south facing slopes, notably at Afton Down, insolation and exposure, combined with patchy rabbit grazing have produced an unusual grassland structure comprising a mosaic of relatively tall and very short grassland, with frequent areas of exposed, weathered chalk rubble. The flora here is extremely species rich with an unusual abundance of horseshoe vetch Hippocrepis comosa, kidney vetch Anthyllis vulneraria and saw wort Serratula tinctoria. A number of orchids are also common including green winged Anacamptis morio, early purple O. mascula, bee Ophrys apifera and pyramidal Anacamptis pyramidalis. These slopes also support very large populations of the very rare early gentian Gentianella anglica and several bushes of juniper Juniperus communis, the only Isle of Wight site. By contrast, the north facing slopes of the downs have a rather taller grassland structure containing abundant cowslips Primula veris and locally frog orchids Dactylorhiza viridis on the thinner soils and scattered gorse Ulex europaeus and bramble Rubus fruticosus on pockets of deeper soils on superficial drift. Superficial Tertiary material covers irregular, broad patches across the crest of the downs and these, too, are dominated by gorse, bramble and locally, hawthorn Crataegus monogyna. The site includes a golf course which extends along the crest of the Downs at their western end. This area is included in the SSSI because the greater part of it remains species rich chalk grassland modified only by the mowing of fairways. At their western end the downs terminate in impressive chalk sea cliffs with stacks and caves. These cliffs and also an adjacent road cutting support plant communities which include a number of rare southern rock crevice species such as wild cabbage Brassica oleracea, rock samphire Crithmum maritimum, yellow horned poppy Glaucium flavum and the very rare hoary stock Matthiola incana in probably its major native location. The entire downland complex is of great entomological importance, notably for its very large populations of chalk grassland butterflies such as chalkhill, Adonis and small blues and for its Orthoptera. The coastline of the SSSI is a key stratigraphic site for the Isle of Wight Chalk, providing a reference section form the excellently exposed Glauconitic Marl of the Lower Chalk through the Middle Chalk of the lower Upper Chalk. As elsewhere on the Isle of Wight, the Middle Chalk is remarkably condensed, much of the middle Turonian being absent. Excellent exposures are seen of the famous Spurious Chalk Rock hardground and the underlying Black Marl Band and Siliceous Nodule Beds. This is the type locality for the Bicavearotiformis Bed, an important marker horizon, which, like the Spurious Chalk Rock, is only developed in the Isle of Wight, Hampshire and Dorset. An essential site for studies of Chalk stratigraphy and depositional events.

Species mentioned