by Neil Hulme

The management of larger woods for rare and declining

butterflies in South East England

IntroductionMany butterflies and moths are in

trouble; they are disappearing from our countryside at an

alarming rate, but nowhere more dramatically than from woodlands. Whereas a few species remain common and widespread, many have become increasingly rare, while others now face local or regional extinction, and some have been lost already. Butterflies and moths have never needed our assistance as much as they do today, but anyone who owns or manages a wood can help.

So why are many woodland

butterflies and moths in such steep decline? These declines are primarily caused by the loss of suitable habitat, reflecting long-term changes in both the type and extent of woodland management.

Specific causes include: the loss of structural diversity through factors such as a decline in coppicing and the widespread planting of non-native conifers, creating large compartments of an even-age; a reduction in the number, extent and connectivity of sunny, herb-rich open spaces; an increase in the extent of

closed-canopy woodland, leading to the degradation or eradication of the shrubby understory and ground-flora.

Further problems exist within the wider landscape, such as the fragmentation and isolation of woodland blocks and the increasingly hostile nature of the countryside between them; the intensive nature of agricultural activity right up to woodland margins, leading to ‘hard’ edges and posing the threat of chemical spray drift; increased browsing by a burgeoning deer population; air pollution and climate change.

This booklet deals with the management of medium to large sized woods, for the benefit of both private owners and woodland managers. In some cases these woods may contain, or have the potential to contain, butterfly species of high conservation concern, including the Pearl-bordered Fritillary, Small Pearl-bordered Fritillary, Wood White, Grizzled Skipper and Dingy Skipper, although additional species may be found in some regions.

Other woods may contain rarer moths, while many more will support the widespread and more common species of butterfly and moth. Even

these are localised or much less common in some areas, and

they may become rarer in the future, so all are worthy

of consideration when managing woods, large or small.

Wherever species of high conservation

concern are present, it is important to look at the bigger

picture, as conservation efforts are always best conducted on a landscape scale. These butterflies and moths are likely to be included in one of Butterfly Conservation’s Regional Action Plans, so please contact your local Branch or Regional Officer, to determine whether the management of your wood can be incorporated within a wider,

co-ordinated effort designed to assist

these high priority species.

Butterflies and moths have never needed our assistance as much as they do today, but anyone who owns or manages a wood can help...

2 BUTTERFLY CONSERVATION Large woodland management BUTTERFLY CONSERVATION Large woodland management 3

Caterpillars are the key

The most pressing issue when attempting to conserve any species of butterfly or moth, is the provision of suitable conditions for the breeding

cycle, and specifically for the often highly demanding caterpillar; the insect’s growth stage.

For the Pearl-bordered Fritillary, this means that the larval foodplant, Common Dog-violet (although other species of violet can be used), must be present in sufficient quantities and growing under conditions which meet the caterpillar’s needs, throughout its development. Seedlings and very young violet leaves are preferred, growing on warm, bare or sparsely vegetated ground, with plentiful leaf and wood litter. This substrate will provide hibernation sites and somewhere for the caterpillars to sunbathe on cold March mornings.

The Small Pearl-bordered Fritillary has a preference for violets growing in cooler, damper, grassier, herb-rich conditions. Abundant and extensive patches of fully established violets appear to be important for this species. These conditions are often found in slightly more mature coppice coupes, replanted clearfells, and in woodland rides and glades. Very recently cleared areas are often too warm and dry for the Small Pearl-bordered Fritillary.

The caterpillar of the Wood White will feed on a variety of plants, including Bitter-vetch, Bird’s-foot Trefoil, Meadow Vetchling and Tufted Vetch. The female butterfly demonstrates a seasonal switch in egg-laying preferences, with those of the first brood (which flies during the cooler, spring period) usually selecting small plants growing in the warmest, fully sunny spots, amongst sparse vegetation and on bare ground, often where a recent clearance has occurred. Conversely, second brood females (flying in high summer) target semi-shaded plants, scrambling through taller grasses and light scrub. This species needs an extensive network of open, sunny rides, with grassy and lightly scrubbed margins which are cut rotationally, and some parts of which are partially shaded.

The Grizzled Skipper is a springtime species which requires wide, sunny, regularly cut rides and woodland glades, and particularly coppiced areas providing warm, dry conditions. Wild Strawberry, Creeping Cinquefoil, Agrimony, Tormentil, Salad Burnet and the succulent shoots of Bramble are all used as foodplants by its caterpillar. Woodland based colonies of this species are much rarer than they once were, although the Grizzled Skipper can still be found in other habitat types, such as chalk grassland and meadows on neutral soils, where areas of sparse vegetation exist.

Although the Dingy Skipper often associates with the Grizzled Skipper, it is most at home where the sward is slightly more overgrown. However, its preferred habitat must contain some bare ground and shorter turf, where its larval foodplants, Bird’s-foot Trefoil (Common and Greater) and Horseshoe Vetch (on downland), can survive and multiply. As with the Grizzled Skipper, this species is far more common in other habitat types, but where it does occur in woodlands, it requires wide, sunny, flower-rich rides and glades.

4 BUTTERFLY CONSERVATION Large woodland management BUTTERFLY CONSERVATION Large woodland management 5

Historically, Hazel coppicing probably provided the habitat most widely used by the Pearl-bordered Fritillary, at least

in some regions, including the South East. However, these days, very little woodland management of this type is performed, and seldom on a sufficiently large scale.

Sweet Chestnut coppice provides a good alternative and can support large populations of the Pearl-bordered Fritillary, despite the usually less favourable ground conditions created, when compared to Hazel. There is a much stronger commercial market for chestnut in the modern era, providing for more traditional products, such as post-and-rail fencing, and the growing biomass (woodfuel) market. The latter may provide a vital lifeline for many of our declining woodland species.

The coppicing of both Hazel and Sweet Chestnut will also provide excellent habitat for woodland-based populations of the Grizzled Skipper, which often flies alongside the Pearl-bordered Fritillary in May. The Small Pearl-bordered Fritillary prefers slightly more mature

coppice, just as it is falling out of favour with its larger relative, and particularly in woods which are damper and more humid.

In order to best service both traditional and modern markets, coppice cycles are typically 6 – 10 years for Hazel and 15 – 20 years for Sweet Chestnut. However, several factors need to be taken into account when consideration

is given to conservation of the Pearl-bordered Fritillary. After just four or five years have elapsed (and sometimes as few as three) since the last cut, coppice coupes become completely unsuitable for this species, so it must rapidly move to a newly cut area.

In South East England this species has developed conservative habits and is quite poor at dispersing around woodlands; research has shown that relatively

small blocks of trees may act as a barrier to movement. Although there are times when population strength and favourable weather may trigger more adventurous behaviour, this species requires easy access to newly created habitat on a regular, shorter term basis.

These new areas must be adjacent or

close to the former block of suitable habitat, particularly if a network of wide, sunny, interconnecting rides is not available, to assist dispersal. Careful planning of the coppicing pattern is therefore a key ingredient in maintaining a healthy population of Pearl-bordered Fritillary.

A perceived conflict of interests sometimes arises in Hazel coppice systems where the Common Dormouse is present, for which the generally accepted advice is to cut successive coupes well away from each other. However, there is always a compromise available, so both dormouse and fritillary can be kept happy by planning a sequence of modest sized coupes based on a wheel or rectangle, which always remains surrounded by more mature, fruiting Hazel (seven years or older) as the inner cycle is worked. This will allow the dormouse easier access to the gourmet menu of flowers, fruit and invertebrates provided by a more varied age structure, within a relatively small area.

The ideal coupe size for the Pearl-bordered Fritillary, where dormice are not a particular concern, ranges from 0.5

CoppiceThe perfect conditions within woodlands are created by coppicing, particularly during the first three years after a coupe has been cut, although many species of moth utilise this habitat type during the later stages of regeneration. It is important to create a mosaic of different age classes.

The coppicing of both Hazel and Sweet Chestnut will also provide excellent habitat

for woodland-based populations

of the Grizzled Skipper...

– 1.5 hectares. Unless an unusually extensive area of coppice is available, larger clearances may interfere with the longer term prospects for the steady, suitably sequenced provision of habitat. Coppice coupes often contain a number of more mature trees of larger species, which were traditionally grown-on to meet timber requirements. These ‘standards’ should provide no more than 20% canopy cover.

With the often inadequately controlled deer population on the increase, newly cut coppice will usually require protection from their browsing action, which can become highly damaging to the re-growth of the crop. Although this might appear beneficial to the butterfly, by extending the lifespan of a coupe, the longer term effects are detrimental, disrupting the vital shade/light cycle and

potentially the future cutting sequence.

Left: There is a strong market for Sweet Chestnut which has both traditional uses, including post-and-rail fencing, and more modern, such as biomass Below: Fallow buck. Unfortunately deer can severely impact regeneration of the underwood and other vegetation when numbers are too high

6 BUTTERFLY CONSERVATION Large woodland management

ClearfellsThe practice of clearfelling

involves the simultaneous harvesting of all the mature trees

in a compartment (>0.25 hectare). Clearfells often provide good habitat for the Pearl-bordered Fritillary and Grizzled Skipper, particularly during the earlier years, even if they are immediately replanted with either soft- or hardwoods. Plantations are often ‘weeded’ until the new crop becomes established, keeping the ground between each row more open; this is advantageous, as it allows the early successional larval foodplants a lengthier period of opportunity, before they are swamped by more vigorous vegetation. Although plantations (particularly those restocked with fast-growing conifers) will soon become unsuitable for these heat-dependent species, other butterflies, such as the Wood White and Small Pearl-bordered Fritillary, will use them for at least a few years more.

The habitat provided by clearfells will generally remain suitable for butterflies for a significantly longer period than coppice, with its useful lifespan depending on the timeframe

for restocking and the species of tree to be grown. However, once the growth of the crop starts to accelerate, and the open areas begin to close up, it might be another 60 years or more before the next phase of felling. At this point, if no accessible, alternative breeding habitat is available, the Pearl-bordered Fritillary and other early successional species will be

lost. Recent case studies suggest that a break of as little as

two years in this part of the cycle may prove

fatal to a fritillary population, unless refuge habitat is provided by permanently open spaces.

A staggered programme

of clearfelling is therefore highly

preferable to more synchronised harvesting,

as a more varied age structure is produced, providing much greater opportunities for butterflies and other wildlife over the long-term. As this sequencing might be difficult to achieve on a sufficiently regular, shorter term basis, it is essential that a supporting network of wide, sunny rides and glades is always maintained.

Left: This clearfell has been fenced to exclude deer and replanted, providing the opportunity to widen the adjacent ride

BUTTERFLY CONSERVATION Large woodland management 9

However, it is too early to determine whether this is the case, and there are a number of measures which can be employed to reduce the potential impact of CCF on those species which rely upon clearings.

Firstly, it is important that even greater consideration be given to the sensitive management of open spaces, including rides, box-junctions and glades; the management advice for which is provided in the next section. Within CCF systems there is also

Continuous cover forestry (CCF) involves a movement away from the more traditional techniques of high forest

management, by abandoning the practice of clearfelling. The main aim is the creation of more diverse woodlands, both structurally and in terms of species composition. The trend towards CCF during the 21st century may, at first sight, raise some concerns about the level of habitat provision for particularly early successional species of butterfly and moth.

the option of employing a regular, rolling programme of scalloping along ride edges, as part of a commercial harvesting plan for quality timber or firewood. These scallops, of generous proportions, can be left to natural regeneration, or be replanted, thereby assisting with the goal of increased stock diversity.

Under a CCF system, in which some degree of canopy cover is always maintained, the main techniques of harvesting include the use of small-coupe clearfells and shelterwood fellings. In small-coupe clearfells, which are generally of c.0.25 hectare in size, a cluster of mature trees are all felled and the clearing is usually left to natural regeneration. Shelterwoods may be larger (up to 2.0 hectares) but are harvested in stages, retaining some of the mature trees until natural regeneration has become established, before being fully opened. Shelterwoods can also be underplanted, as an alternative method of achieving greater stock diversity.

The positioning of both small-coupe clearfells and shelterwoods may have a

significant impact on their value to some species of butterfly and moth. If positioned deep within stands of mature trees, where little sunlight penetrates to the woodland floor, only highly shade-tolerant species (e.g. Speckled Wood) or those which habitually fly at canopy height (e.g. Silver-washed Fritillary, White Admiral, Purple Emperor), are likely to find and utilise them.

However, if these features are positioned close to, or even open onto, woodland rides or other open spaces, their value to particularly the early successional species (e.g. Pearl-bordered Fritillary, Wood White, Grizzled Skipper) is likely to be much greater, simply because connectivity issues are eased. A significant risk in adopting this approach is the high potential for windthrow, which may be exacerbated by tunnelling and vortexing effects. The precise positioning of small-coupe clearfells and shelterwoods, close to woodland margins, must therefore be very carefully considered; an ideal location being on the sheltered, leeward side of a mature stand.

Continuous cover forestry

Background: This small-coupe clearfell has been positioned

very close to a ride, on the leeward side of a mature stand,

allowing access by low-flying, early successional species

of butterfly

10 BUTTERFLY CONSERVATION Large woodland management BUTTERFLY CONSERVATION Large woodland management 11

Rides and gladesThe management of rides and

glades within any type of woodland is vital in sustaining a

population of Pearl-bordered Fritillary in the longer term (see ‘Coppice’,

‘Clearfells’ and ‘Continuous Cover Forestry’), while providing a

more permanent home for the Small Pearl-bordered Fritillary, Wood White, Grizzled Skipper and Dingy Skipper, together with many widespread and commoner species.

RidesRides running west to east are

exposed to sunshine for a longer period each day than those aligned

north to south, so it is particularly beneficial for the latter to be of a width at least 1.5 times the height of the

adjacent tree canopy (at maturity).An extensive system of

interconnecting rides will greatly assist butterflies and moths in dispersing around the wider woodland, particularly when a patch of breeding habitat becomes unsuitable and new areas must be colonised. Well-managed rides and open spaces can also provide refuge habitat, during periods when no suitable coppice coupes, clearfells or smaller clearances are available for immediate colonisation. However, in the longer term, ride and glade habitats alone will generally be insufficient to maintain a population of the Pearl-bordered Fritillary.

Wider rides with a three-zone structure are best, comprising: a central hard surface or short grass zone, the latter being cut annually; a

middle zone of longer grasses, herbs and sometimes Bracken; an outer zone of scrub, saplings and small trees. The outer two zones should be cut on a rotational basis, preferably in a piecemeal fashion, rather than in entire ride-lengths at a time.

The length of the cycles can be modified according to the reaction of the vegetation, which will vary from site to site, and to some extent upon the species being managed for as a priority. A shorter cycle programme (more suitable for Wood White, Small Pearl-bordered Fritillary and Dingy Skipper) might involve cutting the middle zone on a three-year rotation and the outer scrub zone to a five-year plan. A longer programme (more suitable for Pearl-bordered Fritillary and Grizzled Skipper) could be based on cycles of four years for the middle zone and eight or more for the outer. Annual mowing of the entire width of the ride will result in the habitat becoming too grassy for these hard-to-please species. Overly grassy rides can potentially be reconditioned by scarification or heavier scraping, to reinstate areas of bare or sparsely vegetated ground.

Many rides are associated with old ditch-and-bank features. These well-drained, linear microhabitats provide optimal breeding conditions for fritillaries, particularly if south-facing. Brushcutting on a rotational three-year cycle will prevent vigorous shrubs from shading and cooling the ground, and help trigger violet growth.

Above inset: The recent cut into the scrubby strip of this three-zone ride has provided ideal habitat for species such as the Pearl-bordered Fritillary and Grizzled Skipper Below: Rides should ideally be 1.5 times wider than the height of the adjacent crop at maturity, to provide sufficiently sunny margins for butterflies and other warmth-loving invertebrates

ScallopsScallops (bays), ideally 50m long and 20m deep, can be cut into the edges of woodland and long-cycle coppice coupes, preferably along the sunnier side of rides. Their subsequent management can be included as part of the programme for the outer, scrubby strip in a three-zone ride system, or the middle zone, or a combination of the two. The stumps left from felling must be ground down or pulled where the aim is to maintain and manage these open spaces using forest machinery. However, this operation, which comes at a cost, need not be performed if a regular, rolling programme of scalloping is to be employed, as part of a commercial harvesting plan for quality timber or firewood. In such cases the scallops can be left to natural regeneration (or be replanted), to increase stock diversity. A combination of the two approaches is ideal.

Right: The graded profile of this three-zone ride is ideal for butterflies and other wildlife Below right, inset: This ride-side scallop is of generous proportions, but even much smaller examples will significantly improve the structure of a wood, providing warm, sheltered bays for butterflies, moths and other insects

BUTTERFLY CONSERVATION Large woodland management 13

Woodland edges have very high potential to support a wide range of butterflies, moths and other invertebrates, particular those margins which are south-facing and sunny throughout the day. Graded edges are preferable, with a scrubby zone between the trees and more open countryside, which is often agricultural land.

Some owners and land managers may have influence over how this peripheral land is managed, and there are various Countryside Stewardship grants available (see ‘Websites’) to create wildlife-friendly field margins. These greatly enhance the biodiversity of woodland edge habitats, by providing easily accessible nectar sources for woodland species, and by providing a buffer zone from the damage associated with some agricultural activities, such as chemical spray drift. ‘Conservation headlands’, as they are known, will also support their own flora and fauna, and greatly assist woodland species in crossing potentially hostile land, while moving from one wooded area to another.

Woodland edges

GladesGlades should be managed in much the same way as the middle zone of a ride, again being cut in a piecemeal fashion, although some areas can be cut on a longer scrub cycle if the area is large enough. Again, the length of these cycles can be geared to the target species of highest priority.

A disproportionately large benefit to woodland wildlife is gained by the relatively modest amount of work involved in opening up box-junctions (ride intersections), and subsequently managing the bevelled corners on a rotational basis. The permanently open

spaces created by opening up box-junctions should be as large

as possible; particularly where a continuous

cover forestry system is employed and opportunities for early successional species are more limited.

Wherever Bracken is present, be it along ride edges or in permanently open spaces, it is important that the gradual build-up of dead matter is managed, in order to avoid the development of thick, dense blankets supported by standing or semi-collapsed debris. This will involve some system of mechanical breakdown, either as part of a rotational cutting regime or, if necessary, with brushcutters.

Swipe mowers are preferable to flails, as the latter type tends to smash the litter up so thoroughly that it rots down rapidly, rather than leaving the desired patchy carpet of slightly coarser debris. Bracken should be cut on a minimum three-year cycle to suit the Pearl-bordered Fritillary, although a shorter cycle can be employed where the aim is to create a grassier surface for the Small Pearl-bordered Fritillary. Particularly vigorous and extensive stands can be managed via the careful and

localised use of the selective herbicide Asulox, following strict guidelines for purchase, timing of application and storage. It is important that herbicides are not used in the vicinity of watercourses.

The margins of forest roads should ideally be particularly wide, as the immediate edges are subject to periodic upheaval, as the surface is maintained for heavy machinery. This may be damaging to the Pearl-bordered Fritillary, Wood White and other species in the shorter term, but beneficial in the longer. Wider margins provide a safe haven during such activities, and have the additional benefit of keeping the road surface drier, thereby reducing maintenance costs.

The permanently open spaces created by

opening up box-junctions should

be as large as possible...

Left: Box-junctions are seldom this large and their size will be at least partly constrained by the size of the host wood. This one has been created within a large forest. Below: Wide margins provide refuge habitat during periods of upheaval caused by the re-engineering of forest roads. Maintenance costs are also reduced by keeping the road surface dry

Left Inset: Bracken will require rotational management to prevent the accumulation of dense blankets of dead matter. Cutting should occur on a minimum three-year

cycle for the Pearl-bordered Fritillary

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All text and images by Neil Hulme. Front cover: The Pearl-bordered Fritillary; sadly now a rare sight in our woodlands Back cover: Bluebells

Butterfly ConservationCompany limited by guarantee, registered in England (2206468). Registered Office: Manor Yard, East Lulworth, Wareham, Dorset, BH20 5QP. Charity registered in England and Wales (254937) and in Scotland (SCO39268).

Head office: Butterfly Conservation, Manor Yard, East Lulworth, Wareham, Dorset BH20 5QP t: 01929 400209 e: info@butterfly-conservation.org

www.butterfly-conservation.org @savebutterflies facebook.com/savebutterflies instagram.com/savebutterflies

WEBSITES Butterfly Conservation www.butterfly-conservation.orgBuglife www.buglife.org.ukCountryside Stewardship Grants www.gov.uk/countryside-stewardship-grantsForestry Commission www.forestry.gov.ukNational Coppice Federation www.ncfed.org.uk Natural England www.naturalengland.org.uk

Plantlife www.plantlife.org.ukRoyal Forestry Society www.rfs.org.ukSmall Woods Association www.smallwoods.org.ukSmall Woodland Owners Group www.swog.org.ukThe Deer Initiative www.thedeerinitiative.co.ukThe Wood Register (Sussex and Surrey Coppice Group) www.thewoodregister.co.uk Woodland Trust www.woodland-trust.org.uk

FURTHER READINGClarke, S.A., Green, D. G., Bourn, N. A. & Hoare, D. J. (2011). Woodland Management for butterflies and moths: a best practice guide. www.butterfly-conservation.org/3976/woodland-management-for-butterflies-and-moths.html

Forestry Commission England (2009). So, you own a woodland? www.forestry.gov.uk/pdf/so-you-own-a-woodland.pdf/$file/so-you-own-a-woodland.pdf