Woodland fauna

‘Take care of the habitats and the animals will look after themselves’. This is the best rule where the aim is general wildlife protection. The creation and maintenance of floristic diversity is usually the key to animal conservation, since all animal food webs are based on plants, and because the greater the variety of plant life the better the chance of providing the necessary conditions for most animals.

Invertebrates

Diversity of habitats is the main requirement for invertebrates, as their complex life cycles require a range of conditions. Leaf litter contains vast populations of mites, as well as spiders, ground beetles, woodlice, springtails and other organisms which help initiate the decay of leaves and plant debris.

Woodland edges, glades, rides and dead or dying trees are particularly important for many invertebrates. The management of these features is described in Chapter 12 – Woodland habitats. Trees and shrubs vary widely in their importance for invertebrates, with native plants much more valuable on the whole than introduced species. Many adult insects depend on trees and shrubs for food in the form of nectar and pollen. Early flowering species such as willow, and late flowering species such as ivy are especially useful at a time when other food is scarce. Some invertebrates have very restricted distributions, specialised habitat requirements or poor rates of dispersal.

Table 2b, below, lists the number of insect species associated with common trees and shrubs in Britain. An asterisk indicates an introduced species.

Woodland butterflies require specific food plants during their larval stage, as listed below.

Table 2b: TREES AND ASSOCIATED INSECT SPECIES

Table 2c: WOODLAND BUTTERFLIES

Reptiles and amphibians

Of Britain’s six native species of reptile, three are at home in wood margins and hedgerows, as well as heathlands and commons. These are the common lizard (Lacerta vivipara), the adder (Vipera berus) and the grass snake (Natrix helvetica). The common lizard and adder are widespread, while the grass snake is limited to southern and central England and Wales, where it is found mainly in woods and hedgerows near water at low elevations.

Woodland management for reptiles consists mostly of habitat protection and freedom from disturbance. The most important measure is to allow hedgerows, rides, glades and other edge habitats to develop a border of coarse grasses and low shrubs. Where rides and glades are mown, it is worth leaving rough patches or sections for reptiles to bask. On sites where wood and hedge-banks are overgrown, it may be worth cutting them back in places on the south or west sides to let sun reach the ground. Hibernacula can be constructed on suitable sites.

One of the few benefits of rhododendron is that it provides hibernation cover for adders and other reptiles, especially on sandy soils and heathland sites. This should be borne in mind during winter clearance operations, and any known hibernation sites should be left untouched.

The creation of marshy areas and ponds can improve the conditions for grass snakes. Piles of leaves, log stacks or other material which provides undisturbed conditions will provide overwintering sites for reptiles. Loose piles of branches or brash are not particularly valuable for reptiles, because they do not provide the advantage of constant temperature conditions that closer piles do (chapter 12).

Undisturbed and uncleared woodland ponds, with plenty of weed growth and varying depths of water are important for amphibians, especially the great crested newt (chapter 12).

Birds

The management of woodland and scrub for birds concentrates on providing suitable breeding habitat, mainly through the management of the woodland edges, glades and open spaces within the woodland. At the same time, it’s important to recognise that large blocks of woodland usually contain more species, though at a lower population density, than smaller woodland areas. Management work should be timed to avoid disturbance during the nesting season, which is April to July inclusive for most species. Other measures include providing nest boxes or bunches of branches tied to tree trunks, where existing nest sites for hole and shrub-nesting species are in short supply (Chapter 12 – Woodland habitats).

Trees such as oak, which support a large and diverse insect population, supply the most food for insect-eating birds such as tits and tree-creepers. Dense, thorny shrubs are good for nest sites, as are old or dying trees which have holes and loose bark. Ash is particularly good because although fairly short-lived, the dead tree remains standing a long time. Shelter is most important for fledglings and overwintering birds. Clumps or belts of evergreen trees and shrubs can significantly improve the value of broadleaved woods for birds in winter. Ivy, when in its mature, bushy stage, is very valuable for birds and other types of wildlife. Loose piles of brash, especially where overgrown with bramble or other scrambling plants, can provide useful roosts for birds.

Unchecked increases in deer may lead to shifts in the species composition of woodland bird communities, due to the loss of the understorey habitat. Moderate levels of grazing and browsing are thought to be associated with the highest diversities of birds in woodland. Many species of woodland birds have adapted well to the habitat of wooded suburbs, with their gardens and parks, as a replacement for the old wood-pasture habitats.

Mammals

In the past in Britain, there was a much more diverse range of mammals in the woodland ecosystem. Aurochs (wild cattle), elk, red deer and roe deer were the main grazers and browsers, with populations kept in check by bears and wolves. The actions of beaver and wild swine affected woodland structure and succession. Grey squirrel, rabbit, and sika, fallow and muntjac deer were not yet introduced. As well as the direct effect of man’s activities on woodlands, the losses and gains in the mammalian fauna have had, and still have, a very significant effect on woodlands and trees in Britain.

Deer are probably now more numerous than at any time in history, due to the lack of predators, the recent growth in woodland cover and the lack of culling. Winter cereals, an important food source, and recent mild winters have reduced losses. In Scotland, red deer are a major influence in preventing the regeneration and spread of native woodland. In many parts of England and Wales, natural regeneration of woodland is impossible without protection against deer. Parts of Wales and the Midlands, the extremities of Kent and Cornwall, and the Isle of Man and the Isle of Wight are the only areas to remain relatively free. In some areas deer numbers are as high as 40 per sq km. Muntjac have spread rapidly in recent years, and have an effect on the woodland field layer plants as well as young trees. For details of fencing and tree protection, see Chapter 7 – The young woodland.

Foxes have adapted well to woodland loss, and are now numerous in suburban and urban areas. Badgers, now protected against killing, injury or disturbance (Chapter 3 – Woodlands, trees and the law), have maintained active populations in most areas. Favoured places for setts are sloping copses and woods adjoining pasture, where the badgers can forage for earthworms. Well-established setts may be hundreds of years old, and are easy to recognise, with mounds of earth near the many entrance holes, which are at least 25cm (10”) wide. Signs of use are usually obvious in spring, with discarded bedding of hay or bracken outside the entrances, fresh soil and evidence of footprints. All setts are protected by law where they show signs of current use.

Among the smaller woodland mammals, a number of bat species are of management interest because they roost in hollow trees during at least part of the year. The best way to maintain roost sites is to preserve these trees,and where appropriate, to pollard new trees to provide habitats in the future. Provision of bat boxes can provide suitable roosting and nesting sites.

Dormice favour middle-aged to mature coppice or coppice with standards. Young or senescent coppice are not suitable habitats, as they lack the variety of food sources and nesting sites. A 15-20 year cycle is most favourable, with adjacent coupes cut at different times so there is always some suitable habitat. Some mature growth should be left to provide ‘bridges’ across rides and tracks.

Dormice occur in the south of England and in parts of Cumbria. They thrive in warm summers, but numbers can be reduced during mild winters interrupted by cold spells. Botanical diversity is important to provide a succession of food sources through the seasons. In May, oak flowers and various types of pollen may be eaten, followed by caterpillars and aphids in June, ash keys in July, and nuts and berries through the late summer and autumn.

Dormice nest in tree holes up to 10m high in the canopy, and amongst honeysuckle and bramble, with individuals often having more than one nest. They normally breed early in July and again in August. In suitable habitats, nest boxes can be very successful, with perhaps 60-70% of boxes being used. Boxes similar to tit boxes can be used, but with the hole facing the trunk. The only predators are human, so boxes should be put out of easy reach. Dormice may still be present on the margins of otherwise unsuitable woods, so it may be worth putting up nest boxes along woodland edges. For further details see the Dormouse Conservation Handbook (English Nature, 1996). The dormouse is the subject of a Species Action Plan.

Wood mice are one of the most widespread mammals in Britain, but highest densities are found in mixed woodland. The mice prefer areas with low vegetation, fallen branches and logs through which they will make their runways. Wood mice are seed-eaters, gathering the seeds of oak, beech, ash, hawthorn and sycamore for storage over winter. Seeds of other woodland plants, small invertebrates and fungi are also eaten. Wood mice are prey to various species, notably tawny owl and weasel. Numbers fluctuate in an annual cycle, being highest in autumn and winter, during which survival is determined by the size of the autumn seed crop. The rarer yellow-necked mouse is larger than the wood mouse, and spends part of its time in the woodland canopy. Although not aggressive to the wood mouse, the two species are rarely found together.

Woodland adjacent to river margins are important habitats for otters, and where they are thought to be present, disturbance should be avoided.