Forests

transitional woodland | ancient woodland | broadleaf and conifer plantations

 

Transitional woodland

 

Hazel coppice with scattered mature oaks - a transitional woodland habitat ideal for species such as Pearl-bordered Fritillary and Duke of Burgundy.

There are many different types of woodland in Britain, most of which are plantations of oak, beech or conifers, managed by the government agency Forest Enterprise. Only a small number of woods are now privately owned. Some of the latter are managed for timber, some for recreation, and some ( mostly nature reserves ) are coppiced.

In coppiced woodland the trees are cut near the base of the trunk to stimulate the growth of new shoots, used for hurdle making or charcoal production.

These coppiced woodlands are of considerable value as butterfly habitats, as the regular cutting regime stimulates a continuous stable supply of foodplants and nectar sources, and creates a warm sheltered environment that is ideal for butterflies.

Sweet chestnut, cut near base of trunk to stimulate growth of new shoots. After about 8 - 12 years the shoots reach a diameter of about 8 inches, and are harvested again.

Trees which are traditionally coppiced include hazel, sweet chestnut and hornbeam. Hazel coppice is particularly valuable as a butterfly and moth habitat because the fallen leaves decompose quickly. This allows sunlight to reach the ground, encouraging the germination of wild flowers. Hornbeam and sweet chestnut coppice in contrast tends to have a semi-permanent layer of dead leaves carpeting the forest floor, reducing light penetration so the habitat is far less rich in herbaceous plants.

Oak woodland with coppiced hazel. The fallen hazel leaves decompose very quickly, exposing the ground to direct sunlight, which stimulates the germination of violets, primroses, wild strawberry, bugle, trefoils and other larval foodplants.

 

Sweet chestnut leaves decompose slowly, leaving a year-round carpet of dead leaves beneath the trees which stifles the germination of wild flowers. Consequently butterfly diversity and abundance is considerably lower than in actively coppiced hazel woodlands.

 

Oak / ash woodland with coppiced hazel. This small damp but sunny glade provides ideal breeding habitat for Orange tip, Green-veined White and Speckled Wood. Small clumps of nettles growing in sheltered sites like this are chosen for egg-laying by Comma and Peacock.

In most coppiced woodlands a small number of "standard" trees are allowed to reach maturity. These include oak, ash and beech, sometimes supplemented by wych elm, lime or field maple. The shrub layer also invariably includes a number of incidental species such as holly, hawthorn, blackthorn, buckthorn, birch and sallow. A coppiced woodland thus comprises a vast range of trees, shrubs, herbs and grasses, providing foodplants for many caterpillars, and a variety of nectar sources for adult butterflies.

Butterflies confined mainly to transitional woodland habitats include Wood White, Heath Fritillary, Pearl-bordered Fritillary, and Small Pearl-bordered Fritillary. Many other species also use such places as supplementary or secondary habitats. These include Duke of Burgundy, Grizzled Skipper, Dingy Skipper, Holly Blue, Orange tip, Green-veined White, Brimstone, and ( in Scotland ) Chequered Skipper.

 

A recently cleared area of hazel coppice in mid March. By late April the ground will be carpeted with violets, bugle, wood anemone, primrose and many other wild flowers essential as larval foodplants or as nectar sources for adult butterflies. Pearl-bordered Fritillaries love habitats like this.

 

When coppiced woodland reaches maturity the amount of light reaching the forest floor greatly diminishes, the herb layer virtually disappears, and the only butterflies able to continue breeding are Speckled Woods. As one area of the wood matures and shades out the flowers, emerging butterflies of other species will disperse in search of other more suitable breeding areas.

 

Unfortunately most butterfly species have very poor powers of dispersal, and rarely travel more than about 100-200 metres from their emergence site. It can take several years for successive generations to find a new breeding area. During the intervening years they often survive in only very low numbers, breeding along the edges of sunny woodland rides. Woodland managers can make things easier for them by creating a network of wide sunny rides which can be used as migration corridors.

 

If butterfly diversity and abundance are to be sustained it is vital that the coppice cycle is maintained. This ensures a varied age structure and diverse range of habitats, rich in the foodplants and nectar sources on which butterflies depend.

 

Once a woodland gets this dark the flora diminishes, leaving only dog's mercury, bluebells and shade-tolerant grasses. Speckled Woods like this habitat, but other species quickly die out.

 

Conditions similar to those of coppiced woodland can be found in other transitional habitats such as the corridors of regularly cleared woodland beneath electricity pylons, or sunny railway embankments in wooded areas.

 

Ancient woodland

 

The New Forest in Hampshire is a unique area now designated as a National Park. It covers an area of over 57,000 hectares, and is largely managed by the government agency Forest Enterprise. It comprises of a mosaic of heathland, mires, pasture land, conifer plantations, and ancient oak / beech forest.

 

Entomological records indicate that a century or two ago it was the richest area of Britain for butterflies, supporting a vast number of woodland, heathland and grassland species. Sadly that is no longer the case - wild ponies and domestic cattle have been allowed to wander within the forest Inclosures, and grazing has been so intensive that the herb layer of much of the area has disappeared, causing butterfly populations to be decimated.

 

Recently a more enlightened management policy has been introduced and the situation is improving - a small number of Inclosures are now beginning to regain their former glory, with violets, bugle and other wild flowers reappearing. In these Inclosures Pearl-bordered, Dark Green and Silver-washed Fritillaries are flourishing.

 

Mature oak woodland in the New Forest provides habitat for Purple Hairstreak, White Admiral and Silver-washed Fritillary, while the wider rides and clearings are home to Pearl-bordered Fritillaries, Dark Green Fritillaries and grassland butterflies such as Browns and Skippers.

 

Broadleaf and conifer plantations

 

The vast majority of modern forests in Britain are plantations. Some are in private hands but most are state owned, and managed by Forest Enterprise.

These forests are typically broken up into small blocks of between 1 - 6 hectares in area, divided by firebreaks. Often several species of tree will be planted in the forest, but each individual block will consist of a monoculture of conifers ( pine, spruce, larch, cypress, fir etc ), or less commonly broadleaves ( oak, beech or poplar ).

Pine plantations are dark dismal places where butterflies cannot survive

 

Butterflies cannot survive in the gloom within modern pine plantations, but when the trees are felled and sunlight once again reaches the forest floor, millions of dormant seeds germinate, carpeting the ground with violets, trefoils and bugle - the nectar sources and larval foodplants of butterflies.

 

This abundance of food sources however is very short-lived, because within about 4 or 5 years, the new trees will have grown sufficiently to shade out the herb layer.

 

If butterfly colonies are to survive, it is vital that plantations are managed so that new clearings are created every year or two, to supply a continuous availability of suitable breeding habitat. It is also essential to give the butterflies a helping hand so that they can easily and quickly find their way to suitable new areas of breeding habitat. This can be done by creating wide sunlit rides which act as migration corridors between the forest blocks. Scalloping ride edges, and enlarging intersections provides additional temporary habitats where butterflies can breed.

 

In larch plantations much higher levels of sunlight reach the forest floor, allowing violets and other larval foodplants to grow.

 

Timber nowadays offers little financial return, and this fact, together with increasing public demand for leisure facilities has brought about a change in Government forestry policy. The tendency now is for the plantations to be periodically thinned, rather than clear-felled and replanted, and for the woodlands to become retained for their amenity value - many former timber plantations are now Country Parks.

 

The edges of the tracks and rides in plantations are often planted with a narrow strip of amenity broadleaves such as oak, sallow, buckthorn, field maple and wych elm. There are also often a few ornamental species such as scarlet oak, sycamore, lime and cherry.

 

Most woodland blocks are edged with drainage ditches and small embankments, while other habitats may include small semi-permanent glades, grassy avenues, riversides and ponds. A modern woodland is thus comprised of a multitude of sub-habitats which support many native trees, shrubs and bushes. The structure of the woodland usually ensures that there is an abundance of sheltered sunny areas, supporting a rich variety of grasses and wildflowers growing along the ditches, embankments and ride edges.

 

Wide grassy forest rides can be thought of as "linear meadows". Vetches, trefoils and violets growing along the ride edges are used as larval foodplants by many species, as are buckthorn, sallow, dogwood and holly. Nectar sources also abound - hemp agrimony, thistles, bugle and bramble each attracting numerous butterfly species.

 

The consequence of this rich botanical variety is that many plantations in southern Britain support not only true woodland butterflies such as Silver-washed Fritillary, Purple Emperor, White-letter Hairstreak, Purple Hairstreak and White Admiral, but also often have populations of species normally associated with scrubby grassland - e.g. Dark Green Fritillary, Brown Hairstreak, Grizzled Skipper, Dingy Skipper, Large Skipper, Marbled White, Meadow Brown, Ringlet and Gatekeeper.

 

Most species however exist at very low densities and there is an absolute and immediate need for landscape-level conservation management to be implemented to prevent their continuing decline and ultimate extinction.

 

 

Almost every British and European species of butterfly is declining rapidly in numbers, due in most cases to loss or degradation of habitats.   You can help to reverse the decline by supporting conservation organisations which purchase and manage habitats as nature reserves, and which lobby government at local, national and international levels, often very successfully, to bring about changes in farming, forestry and urban development policies.   Please contact the conservation organisations for advice on how you can help protect British and European butterflies and their habitats. You may be able to offer practical help e.g. by monitoring butterfly populations or helping to manage nature reserves. Donations to these organisations enable them to employ ecologists and biologists. Even if you are unable to provide such help, merely having your name on the membership list can be a powerful tool for conservation organisations wishing to demonstrate the levels of support they have for their policies.