Making the connections - our Cerne Valley Commuity Landscape Project

Joining up the chalk downland habitats in the Cerne valley

Since 2012 a team of volunteers and contractors working through EuCAN Community Interest Company and Butterfly Conservation has been working on the chalk downland sites between Lyons Gate and Godmanstone to remove the invading bushes and trees that are threatening to destroy the last vestiges of this incredibly biodiverse habitat in this area of Dorset. The plumes of smoke from the hillsides on Thursdays between September and March cannot have gone unnoticed.

This work has been generously funded by the Patsy Wood Trust and the landowners themselves – these funds have enabled EuCAN to bring the mixed bunch of contractors with power tools, people from neighbouring towns with learning difficulties and in recovery from mental illness, as well the carers and a number of local EuCAN and Butterfly Conservation volunteers. It has all been great fun (especially the soup, sausages and baked potatoes for lunch and the cakes for tea!) and we have been extremely pleased with the results. To date, we have held over 100 sessions on 11 different sites and have involved 170 different people. Not only have we made a great impact on the ecology of the sites we have visited, but the participants have learned new skills, seen some wonderful wildlife and have had the benefit of the fresh air and exercise that probably they would not normally get (most of our sites are on 45˚ or 60 ˚ slopes, often very challenging!).

But why is this amount of effort necessary now? It has not always been the case and I shall try to explain why….

Chalk downland is possibly the richest habitat in Dorset – one quick glance at the grassy sward on the slopes round the Cerne Giant will reveal perhaps a dozen obvious species of plants; if you look closely and count the species in a square metre you should be able to distinguish well over twenty, even thirty if you can identify the different grasses. They won’t all flower at once – the Cowslips, Early purple orchids and several violets tend to be first to bloom, while the vetches, Fragrant and Bee orchids and yellow dandelion-like flowers come out later and the Devilsbit scabious, Harebell, Clustered bellflower and Autumn hawkbit blooms signal the end of the summer. Many of these plants are the caterpillar foodplants of the specialist butterfly and moth species that are so characteristic of this habitat

Adonis Blue

Adonis Blue

Chalkhill_Blue_male_2

Chalkhill Blue

Blues like and Adonis and Chalkhill Blues (above) need Horseshoe Vetch for their larvae; Birdsfoot Trefoil (sometimes called Eggs and Bacon) is the foodplant of the Common Blue, Dingy Skipper and the Burnet moths (those dayflying beetle look-alikes that buzz about the slopes in June and July). Small Blues favour Kidney vetch and the Duke of Burgundy Cowslip or Primrose leaves. One of the scarcest butterflies to be seen on the slopes of Giant Hill in May and June is the Marsh Fritillary whose caterpillars need Devilsbit scabious: the female lays her eggs in batches of 50-200 and the larvae live in crowded clusters on the leaves of the plants. In recent years this species has done very well on some of its local sites.

Marsh Fritillary Euphydras aurinia

Marsh Fritillary

As well as being important for butterflies and moths, the chalk downland on Giant Hill also supports good populations of Glow-worms, specialist bee and wasp species (not the stinging sorts!) – including the beautiful little bee, Osmia bicolor, which lays its eggs in the empty shells of downland snails (featured in 2014 in a wonderful short film on the One Show), not to mention the many species of ants (one of which, the Yellow Meadow Ant, lives in colonies in the grassy mounds that are a feature of our ‘warty’ downland slopes). See this link for short Youtube films from this programme.

Osmia bicolor

Osmia bicolor (photo: BWARS)

We are very fortunate to have a number of well-known and highly regarded chalk downland sites in this area of Dorset – good examples are Black Hill, Yelcombe and Giant Hill above Cerne Abbas; Lankham Bottom Butterfly Reserve above Cattistock and Hogcliff National Nature Reserve above Frampton and Maiden Newton.

But look at a map of Dorset and the UK and you will see that the chalk stretches from west Dorset at its SW corner to Yorkshire and Norfolk at the northern end and into Kent to the east. So why is this habitat such a rare commodity? In centuries past, the downs were grazed by large numbers of roving sheep flocks, while only steep flinty, less productive slopes would have been maintained as woodland (some of these ancient coppices still remain). Hawthorn, gorse and bramble would have been far less abundant, some it cropped as furze for fires, but most of it nipped off by the flocks as they passed through. Our ancestors would have cultivated some of the hilltops and the slopes but on a very small scale as the human populations were so low. You can still see relics of the celtic field systems in the Cerne, Sydling and Frome valleys, many of them pre-Roman. Chalk grassland and the butterflies and other wildlife it supports would have flourished from east Devon to Kent to Yorkshire.

Previously open stretches of chalk countryside were divided up by the 18th century enclosures but it was after the end of the second world war that the widespread arable cultivation of downland  took  place, with the government encouraging farmers to ensure that we would never again be vulnerable to being starved into submission. The scale of these operations has accelerated enormously during the last fifty years with the help of advances in technology which have not only given the farming industry larger more powerful machines to work on the steeper slopes, but also the chemicals to ensure that rivals for their growing space like insects and weeds (aka wildflowers) have become reduced to a minimum. Chalk soils drain very freely so fertilisers tend to get leached out of the ground by the rain. The free drainage and lack of organic matter in the soil mean that arable crops have to be treated continuously with fertilisers as well as pesticides and weedkillers. The consequence of this arable revolution that began at the beginning of the 50’s is that chalk downland habitats have become reduced in Britain by over 90% , with the remaining sites now being restricted to steep slopes. Very few flat downland sites are to be found now – Martin Down on the Dorset/Hampshire border and large parts of Salisbury Plain still survive thanks to the involvement of the military.

And it is not just human factors that have led to the destruction of the orchid- and butterfly-rich habitats that we appreciate so much. Nature has done its bit too. Many of the arable farms on the chalk had no place for livestock, so the remaining steep patches of downland did not get grazed by animals as they would have been in previous centuries. In consequence, on these effectively abandoned oases of chalk grassland, there has been a huge increase in the growth of gorse and thorn which gradually develops into thickets and ultimately into ash, sycamore and oak woodland. These can be wonderful habitats in themselves providing nest-sites for birds and niches for species which are not found in open grassland. However, once the downland is lost by natural succession to climax woodland, the soils change irreversibly and the original habitat is very unlikely to to come back for a long time. Hence the importance of preventing the invasion of downland by thorn and gorse scrub.

So there are many isolated fragments of chalk downland habitat between Lyons Gate and Dorchester and stretching westwards to Eggardon Hill. They are separated by acres of inhospitable arable land, now effectively devoid of the wildlife that once flourished there, and are themselves threatened by a tide of bramble and thorn which is tending to turn them into woodland. All these processes are happening very rapidly. It doesn’t take long for the chalk flora to vanish under the scrub and the smothering carpet of ivy that frequently accompanies it.

We would like to open up a chain of connecting areas of chalk grassland between Dogbury above Lyons Gate and Charminster. Many species of insects and other wildlife will not cross habitats that are unsuitable for them, even small distances, so by producing a linked up chain of suitable sites for them, we will be greatly increasing the territory available to them and thereby their chances of survival, so that our children and grandchildren can continue to appreciate them as we have done. We will always looking for new volunteers – you would be very welcome to help with the cutting and burning up or (very important!) to make the tea….

Further information can be found on the EuCAN website http://www.eucan.org.uk/uk/dorset/cerne-valley-project/