Dorset Habitats: Chalk downlands
Colin Varndell looks at the landscapes, the flora and the fauna of Dorset’s chalk downlands
Published in May ’12
How often have we stood on one of Dorset’s impressive hills like Eggardon or Hambledon, admiring the open countryside stretching away into the distance before us? These patchworks of green fields may make magnificent scenery, but the meadows and pastures we view today are not what they once were. In fact, from the point of view of native flora and fauna we are viewing little more than hostile wasteland. The advent of chemicals, driven by market forces to eradicate native wild plants and increase the yield of crops, have turned these once flower rich meadows into sterile deserts. While standing on the ramparts of Eggardon, it is only the habitat immediately beneath our feet, which now remains unspoilt or ‘unimproved’.
Of all Dorset’s various habitats, none is so florally prolific as unimproved chalk grassland. This is a semi-natural habitat which has become increasingly rare due to urbanisation and changes in farming methods. The chalk grassland which remains on many of Dorset’s larger hills support a wealth of diverse flora and associated insect life, much of which cannot be seen elsewhere in the county. Traditionally, these hillsides are managed by sheep grazing in order to maintain the diversity of the sward. The environmental conditions endured by these habitats include summer drought and winter frosts, together with poor soil quality. These factors together with the regular grazing ensure that no individual species is able to dominate the sward, therefore resulting in a very wide range of plants. The management of these areas requires a fine balancing act as the grazing regime must allow the chalk loving species to flourish but also keep a tight hold on scrub which would soon smother these habitats if allowed to take hold.
Chalk is a soft rock made up from the remains of sea creatures laid down over a thirty million year period when the sea rose to between 200 and 300 metres higher than it is today. These deposits left a swathe of chalk stabbing diagonally across Dorset from north east to south west, with a further finger running from Weymouth eastwards to Old Harry.
Over time, thin soil deposits covering the calcium rich chalk made this landscape ripe for agriculture. As a result, the vast majority of chalk is now either under intense cultivation or built upon. However, many of the hills of Dorset have proved to be too steep to plough and have remained as chalk grassland habitats, erupting in a mosaic of varied plant life during the summer months. The wild flowers of chalk grasslands are numerous and include such gems as harebell, lady’s bedstraw, toadflax and squinancywort. Cowslips, typical of the chalk downlands, often occur in vast numbers followed by a succession of orchids which include twayblade, greater butterfly, common spotted, pyramidal, bee and fragrant. Other wild plants to be found on these chalky slopes include small scabious, ploughman’s spikenard, carline thistle, dwarf thistle, wild thyme, eyebright, bird’s foot trefoil, wild mignonette, clustered bellflower and melancholy thistle. The national rare autumn gentian, although easily overlooked due to its size, occurs throughout these chalk hills in abundance in late summer.
On these flower-rich chalk downlands the associated insect life is also of great importance. Many insects have evolved to co-exist with the chalk-loving flora, especially some butterflies and moths like the Adonis and chalkhill blues, silver-spotted skipper and wood tiger moth.
The silver-spotted skipper is a real gem of Dorset’s chalk hills. At first it gives the impression of a tiny day flying moth, but closer observation reveals its typical butterfly antennae tipped with orange and the silvery spots on the undersides of the wings. This is a restless insect, flying rapidly between anthills to sip nectar from scabious, hawkbits and dwarf thistle. Anthills are a typical feature of the thin soils on chalk and are constructed by the yellow meadow ant. Another easily overlooked insect found here is the brown argus butterfly. This tiny butterfly is a member of the blues family and may be mistaken for a female common blue. In some years, the brown argus can be very abundant. Look for it on July evenings as it suns itself on grasses in sheltered pockets. Invariably, it will do this upside down with wings spread out flat to gain maximum benefit from the last rays of the sun.
The chalkhill blue is an insect occurring in July and August in Dorset. This pale, silvery blue butterfly feeds mainly on scabious, knapweeds and thistles. It lays its eggs on vetches, especially bird’s foot trefoil. In some years this insect can occur in huge numbers. Walk the ramparts of Eggardon, Hod Hill or Maiden Castle in late July and you may be treated to clouds of these beautiful insects flying up from the vegetation as you approach.
The wood tiger moth is especially abundant in the sheltered bowls of the chalk slopes around Cattistock. This is an attractive day-flying moth which is easy to observe as it frequently rests at ground level. The grizzled skipper butterfly is also abundant on these slopes. Other invertebrates occurring in good numbers on the chalk grasslands include longhorn beetles, crab spiders and meadow grasshoppers.
There do not appear to be any bird species specifically (or rather exclusively) linked to chalk grassland, but the nature of the sward and the plant life it supports does attract certain species. For instance, goldfinches and linnets are attracted by the seeds of thistles and knapweeds. In late summer, flocks (or charms) of tinkling goldfinches flutter around the flower seedheads. Skylarks and meadow pipits both nest in the thicker vegetation and their songs enhance the atmosphere of early summer. The anthills which quickly become colonised by wild thyme and rock roses also attract that most flamboyant of birds, the green woodpecker. It probes the anthills with its long sticky tongue as it searches for ant eggs, its staple diet.
Walking on Dorset’s chalk downlands in summer is one of the true delights of living in this county. The chalk hills of Fontmell and Melbury in the north and Eggardon and Cerne in the south provide a small glimpse of this unique and much diminished habitat for which we are now the custodians. Long may it remain so, but I often wonder, if we had learned much earlier of the importance of these habitats, how much more might have been preserved?