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M A M M A L S AND THE CONSERVATION MANAGEMENT OF WOODLANDS. P. A. MORRIS Woodlands are particularly important for British mammals. Over half our species are strongly associated with woodland and several are found almost nowhere eise. In terms of practical woodland management, mammals may be divided into three categories: Numerous and widespread species that are likely to remain so, almost irrespective of what management policies are adopted. They include the ubiquitous wood mouse (Apodemus sylvaticus), bank vole (Clethrionomys glareolus) and common shrew (Sorex araneus). These species are of low conservation priority, because they are little threatened by change. It is not necessary to prescribe particular woodland management strategies for them, as they will survive so long as the woodland itself does. 'Low priority' does not imply that they are unimportant, on the contrary. Several woodland small mammals typically reach population densities in excess of 100 per hectare and form key prey species for owls and carnivorous mammals. The rodents may also be very important in woodland ecology through dispersal of acorns and the destruction of seedlings (Corbet, 1974).

A second group comprises other common and widespread species, similarly not in need of active conservation, but whose activities and numbers are such that they constitute a significant threat to wildlife conservation interests. Foremost among these are the deer. Five of the six British species are primarily woodland animals. All are substantially bigger than the average size for British mammals (so have greater environmental impact), all are increasing in numbers and some are already sufficiently numerous to Warrant pest status (Harris et al., 1995) due to the impact they have on V e g e t a t i o n communities.

The muntjac (Muntiacus reevesi) is spreading rapidly in England (Chapman, Harris & Stanford, 1994) and threatens amenity and conservation woodland. In Scotland red deer (Cervus elaphus) are causing concern in both forestry plantations and ancient Caledonian pinewoods (Callander & MacKenzie, 1991). Deer have a major impact on regenerating woodland (Prior, 1983) and may seriously compromise commercial and conservation coppicing projects.

Four of our six deer are introduced species, to which the woodland community has not had time to become adapted. Nowhere eise in Europe do woodland ecosystems have to resist the onslaught of so many different species of deer.

Where the conservation value of coppicing is seriously compromised by browsing deer, culling is often instigated as a management tool (de Nahlik, 1987), but may result in other problems, see below. An alternative is 'dead hedging', using surplus poles cut from coppice stools to create twiggy barriers around individual stools or coppice coupes. This may be effective in protecting regrowth, at least until some of the new poles have grown beyond reach of deer.

However, these activities increase the cost of management, or decrease the amount of conservation work that can be done by a given number of volunteers.

The rabbit (Oryctolagus cuniculus) is strongly associated with woodlands, especially the margins. Following decrease in the 1950s due to myxomatosis, it is now increasing rapidly (Tapper, 1992) to attain significant numbers once

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again. Rabbits suppress woodland regeneration and selectively remove elements of the woodland ground flora that might be of importance in their own right or as key food plants (e.g. for insects). The grey squirrel (Sciurus carolinensis) is another introduced species that is having a negative effect on woodlands. Bark Stripping by squirrels can cause significant economic loss, although it is hard to escape the conclusion that this 'squirrel problem' is also a forester problem, in which ideal and highly unnatural conditions are created and it is hardly surprising that the adaptable grey squirrel exploits the opportunities provided. The native red squirrel (S. vulgaris) also gnaws bark, but has less impact because it does not (and probably never did) reach the high densities, sometimes exceeding 4 per hectare, attained by the grey.

With these 'pest species', management is based upon the animals being injurious to conservation interests and a reduction in numbers or impact is sought. Control of grey squirrels is frequently attempted, using an anti-coagulant poison, delivered by deploying hoppers charged with poisoned grain bait.

This is cheap, but illegal in counties where the red squirrel still occurs. Poisons are likely to affect non-target species. Even where precautions are taken, spillage of poisoned bait is a danger to other rodents and carnivores are at risk from secondary poisoning if they consume a poisoned animal. Poisons are probably not a significant threat to the rare dormouse (Muscardinus avellanarius) for it does not normally feed on the ground or eat grain baits, the usual carrier for anticoagulant poisons.

Poisons are increasingly regarded as unacceptable management tools (see for example, Bryant, 1994), and shooting (especially of deer) is also likely to inflame public opinion, particularly where it is carried out in nature reserves.

Controversy may spill over into public meetings and protest, highly destructive to the cohesion of voluntary organisations who may own the reserves or be responsible for their management. Other management options should be sought and there is much scope for fresh imagination to be applied to this area. For example, deer might be dissuaded from occupying particular woodlands by regulär parties of beaters scaring them away. Electric fencing could be used to exclude them, at least from highly sensitive areas. Perhaps hazel coppicing could be replaced by a form of pollarding, retaining the conservation advantages, but keeping regrowth out of reach of deer. More research is required into the formulation of effective repellents. Perhaps in the long term, genetic engineering will allow tree clones to be developed that have highly distasteful bark, encouraging squirrels and deer to leave them alone, at least in commercial forests.

The third group of mammals are declining species which require active conservation management of woodlands to ensure their survival. These include the red squirrel, dormouse and pine marten (Martes martes). It is possible that the yellow necked mouse (Apodemus flavicollis) also comes into this category. This is a species of ancient woodland, apparently preferring older coppice (Hicks, pers. comm.). If older coppice is beneficial, then yellow necked mice should have become more abundant this Century as coppicing decreased.

However, comparisons with the past are difficult as it was only recognised as a British species less than 100 years ago. It is now relatively rare (Harris et al., 1995) and its distribution is very patchy in both space and time. It is difficult to

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understand how such a thinly spread species can maintain an integrated population, especially when specimens have not been recorded in the large areas that separate known localities. Its numbers appear to fluctuate, increasing the vulnerability of isolated populations, yet they persist. It is also unclear how this species survives sympatrically with the closely related wood mouse without one or other suffering competitive exclusion. It is possible that the yellow necked mouse is an arboreal species, which is relatively infrequently caught in traps set on the ground. Perhaps larger catches indicate (seasonal?) failure of arboreal food resources, leading to greater activity on the ground and larger numbers being caught. Perhaps the patchiness and apparent scarcity of this species are an illusion caused by irregularity of capture. As yet, its ecology is not sufficiently well understood to formulate a management prescription.

Much the same applies to the pine marten, which has disappeared from most of its ränge in Britain and seems to require very large areas of woodland to sustain its thinly-spread populations. Current research includes studies aimed at establishing the potential for reintroduction, perhaps to large areas of conifer plantation in the north of England.

The badger {Meies meles) is a controversial species. It is strongly associated with woodland and has fĂźll legal protection. Its setts are also protected and there are no significant natural predators. The total British population is about 250,000 (Harris et al., 1995), with strong suggestions that numbers are increasing locally, at least in some areas. As badgers are large and excavate substantial burrows, their activities sometimes cause problems, especially where urban encroachment leaves the badgers with insufficient space and in close juxtaposition to houses, gardens and valuable crops. It is claimed that the badger is becoming too numerous and no longer W a r r a n t s legal protection. However, repeal of the relevant legislation would probably only result in increased (and often inhumane) persecution where badgers are already scarce, with little effect in areas where they are abundant. However, it remains a relatively scarce species in East Anglia, apparently a legacy of effective suppression by gamekeeepers during the past 100 years (Harris, 1993).

The wolf (Canis lupus) and bear (Ursus arctos) were two other native woodland species that are now extinct.

The Dormouse The dormouse is a declining species whose fortunes depend crucially on how woodlands are managed. Its distribution appears very patchy, especially in Suffolk (where few localities are now known), an impression heightened by the difficulty of obtaining positive records of this elusive species. It is a nocturnal, arboreal animal which feeds almost exclusively on flowers (pollen and nectar), insects (caterpillars, aphids) and fruits, preferring soft mast such as blackbernes to hard mast; although hazel nuts are the principal food upon which it fattens up for winter (Bright & Morris, 1993). Each of these becomes seasonally available as the summer progresses, so the dormouse has to exploit a sequence of tree and shrub species. As it rarely travels more than about 60m from its nest, a Wide variety of plant species have to be highly intermixed to provide suitable habitat (Bright & Morris, 1991a; 1991b). Such conditions are best provided by ancient semi-natural woodland, particularly where coppice management takes

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place. Coppicing maintains a vigorous understorey, but thinning of the emergent trees is also important to avoid shading of the shrub layer and consequent decline in its productivity. Naturally regenerated woodland is also often poor habitat as all the trees are of similar age, grow very densely and cast a deep shade suppressing the vigour of the understorey. (See Plate 1) An unshaded understorey is probably the most important factor determining good dormouse habitat (Bright & Morris, 1990). The major decline in woodland management, especially coppicing (FĂźller & Warren, 1990) since 1900, has led to many of our ancient woodlands becoming shaded and dominated by dead wood and eventually replaced by high forest with only a sparse and unproductive shrub layer. These are poor conditions for the dormouse, and its decline has coincided with the decline of woodland management this Century. The dormouse is now absent from seven counties where it was found only 100 years ago (Hurrell, & Mclntosh, 1984; Bright, Morris & Mitchell-Jones, in press).

Other factors have contributed to dormouse decline, notably the complete removal of ancient woodland and its replacement by farmland, built environments and plantations. The latter are unsuitable for dormice, except in the short term, as they tend to be species poor and heavily shaded.

Inappropriate management also threatens the dormouse. For example, the ancient rights of pannage which allowed commoners to have free ranging pigs in the woods during the autumn. The intention was that the pigs would feed on fallen mast, but in doing so they were highly likely to find and eat dormice which hibernate on the ground, their nest often protected by nothing more than a covering of a few leaves. Pigs and cattle also trample the woods, again a threat to dormice in their hibernacula, but also causing significant damage to understorey shrubs. Many of the Welsh woodlands that still have dormice present are endangered by free ranging sheep, whose hooves and teeth suppress regeneration, leading to park-like conditions that are unsuitable for dormice.

Coppice management has been reintroduced to many sites to generate a commercial pole crop, but rotations are often short. Similarly, 5 - 7 year rotations have been recreated by conservation managers to encourage biodiversity.

The coppice is often managed on a short rotation to encourage ground flora and many butterflies which have become rare as a result of closed and shady conditions. Sometimes this type of coppicing has been spectacularly successful, for example in boosting the waning population of the heath fritillary (Mellicta athalia) in Kent (Warren & Thomas, 1992). Ironically this too has threatened the dormouse in many cases. Hazel rarely fruits at under seven years old, so short rotations are of poor value to the dormouse.

Removal of sycamore is another conservation management option that is often exercised for the benefit of many species. In fact this tree provides a very high biomass of insect food for dormice, as well as edible flowers. Dormice can utilise sycamore in secondary growth and this species is probably more use (at least in small numbers) to dormice than some native trees, creating a potential conflict of conservation priorities.

Conservation management practices also often include creating wide sunlit rides, but again this is detrimental to the dormouse which is highly reluctant to cross such open spaces. Wide rides may reduce access to key food resources at critical times. Narrow rides, with occasional bays and Clearings and occasional

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trees meeting overhead are better. Coppicing leaves large trees (with their food resources) isolated by open space; small and scattered coppice coupes are preferable to large cut areas adjacent to others that have not yet regenerated fully.

Understanding the ecology of the dormouse has made possible the publication of a prescription for woodland management (Bright & Morris, 1989; Bright, Morris & Mitchell-Jones, 1996) upon which the current Species Recovery Programme (Whitten, 1990) for the dormouse is founded.

Young coppice may be rieh in food sources for the dormouse but lacks tree holes which dormice seem to need, particularly in bad weather. Nest boxes provide an attractive Substitute and dormice take to them readily (Bright & Morris, 1989; Bright, Morris & Mitchell-Jones, 1996). Nestboxes also then provide access to the animals, allowing population monitoring. Information on population size and breeding success is now available annually from a nationwide series of 'Key Sites' where nestbox monitoring takes place. From this we should learn more about the effects of different woodland management regimes on aspects of dormouse success. Inexpensive dormouse nestboxes are available form the Pathway Sheltered Workshop, c/o R Johnson Ltd, Watlington Rd, Cowley, Oxford 0X4 5LN, but are unlikely to be very effective unless large numbers (at least 20) are deployed.

Suggested prescription for conservation management for the dormouse: 1. Ensure high species diversity is maintained in the trees and shrubs; hazel, oak and honeysuckle should be abundant.

2. Implement thinning to ensure the understorey does not become heavily shaded by taller trees.

3. Coppicing of hazel (and other species) is beneficial; but coupes should be small and widely scattered.

4. Coppice rotations should be at least 10 years, ideally 12-15 years, depending on fruiting and shrub vigour.

5. Suitable nestboxes should be available in significant numbers.

6. Farm animals should be excluded.

The Red Squirrel The British red squirrel has been described as a separate sub species (S. v. leucourus), characterised by a seasonal bleaching of the tail. However, multiple introduetions from the Continent now result in a genetically mixed population.

It has fßll legal protection from trapping, shooting and all forms of interference. However, this is no defence against the principal threat to its survival which appears to be that it is less well adapted to many of the habitats that Britain now offers than the American grey squirrel, which was introduced here at the turn of the Century. Decline of the red squirrel is unlikely to be wholly and directly due to the introduetion of the grey, having begun prior to its arrival or at least before it became widespread. There is no evidence to support suggestions that disease, imported with the grey, was responsible nor that the larger grey squirrel has physically 'driven out' the native species through aggressive interaction. Nevertheless, the native species has disappeared from most of its former ränge in England and Wales over the past fifty years, usually within 15-20 years following the arrival of greys.

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Replacement of red squirrels by greys is due to more subtle factors. The grey squirrel is better adapted to life in fragmented and deciduous woodland habitats. These are now the predominant woodlands available over much of Britain today. Once the numbers of red squirrels declines, for whatever reason, greys replace them. In pure coniferous woodlands the balance of competitive advantage may not be tipped so much in favour of the grey, but elsewhere the red is vulnerable. Outside Scotland, red squirrels are unlikely to persist if present trends continue, except on some islands and perhaps in a few isolated areas of forest. Suffolk is one of the last English counties where the species still occurs, but probably not for much longer. The Victoria County History of Suffolk, published in 1911, described the red squirrel as being very abundant at one time and "an enemy" of game interests. Arnold (1993) showed it was still present in most of the 10km squares in Suffolk between 1960 and 1974, but occurred in only 4 (at the extreme north west of the county) after 1975. Red squirrels may still exist elsewhere in Suffolk, but in such small numbers that they are unlikely to persist much longer.

As with many other British mammals, estimating the total population size is difficult, but there are probably only about 161,000 remaining, less than 20% of them in the whole of England (Harris et al, 1995). However, total numbers are less important than numbers present in a particular forest. Since red squirrels live at low density, a minimum viable population will require a large tract of continuous woodland. Such areas are few, and remaining squirrel populations in small woods are likely to die out owing to chance events and demographic instability. However, it is not clear what constitutes a minimum viable population of the red squirrel, nor what is the minimum area needed to sustain it.

The red squirrel has received less attention than it deserves and conservation measures are hampered because many of the studies that are most needed require long-term work not easily accommodated in traditional three year research funding cycles. It is primarily a species of northern conifer forests, feeding in the tree canopy and spending about 70% of its time off the ground.

Its food, particularly pine seeds, is available at the tips of thin branches. The red squirrel thus needs to be lightweight and long limbed and cannot afford to carry substantial fat deposits and therefore cannot easily survive periods of food shortage or inclement weather when foraging success is curtailed.

As an arboreal feeder, the red squirrel needs a continuous tree canopy, over a large area. Forest fragmentation (e.g. by cutting wide swathes for roads, railways, pylon lines and widesprerad replacement by farmland) is a disadvantage.

Small areas of remnant woodland may provide sufficient food in good years, but seed crops (especially in deciduous woodlands) are greatly reduced in some years, posing a severe threat to survival, particularly in small isolated woodlands.

Conversely, the grey squirrel collects much of its food from the ground and is thus less reliant on the relatively restricted food sources in the canopy. It is well adapted to deciduous forest, having originated in this kind of habitat, and it can accumulate substantial fat deposits in times of plenty, enhancing survival during inclement weather or poor mast years. The grey squirrel can also digest acorns and feeds extensively on them. Acorns are not favoured by the red squirrel and it cannot digest them adequately (Kenward & Holm, 1989). Since

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the oak forms a major component of many of our forests, and acorns are one of the principal foods available, the red squirrel is seriously disadvantaged by being unable to utilise this resource effectively. Hazel nuts are exploited by both species, but as greys normally live at higher population densities the reds will get only a minority share of the hazel crop where both squirrels co-exist.

Periodic failures of food crops may have contributed to population declines which are a feature of the history of British red squirrels. Whilst it remained the only squirrel present, recovery was possible, but introduction of a robust competitor was a major setback. The balance, already weighted heavily against the red squirrel, has now shifted decisively for the worse and replacement by the grey continues, especially in deciduous habitat.

In pure conifer forest, advance of the grey squirrel is less dramatic. Plantation forestry (using mainly conifer species) appears to offer a lifeline to the red, but many plantations are on poor soils and at high density, resulting in poorquality food crops. Moreover, the trees are often felled before they are old enough to yield the maximum quantity and quality of seeds for the squirrels to eat. A further disadvantage is that conifer plantations are unpopulär and many (e.g. in East Anglia) have been screened by planting a fringe of hardwoods.

These provide corridors aiding rapid dispersal of greys and also habitat to support grey squirrels in areas where they might otherwise be at a relative disadvantage.

Squirrels breed early and their success in raising young depends very much on body condition in over-wintering females, determined by food availability the previous autumn. While both species can produce two litters per year, reds rarely do so. The result is that annual net recruitment per female, is about 0.6, half the rate in grey squirrels (Holm, 1990). Better feeding for reds may enhance reproductive success. Special food hoppers, designed to provide food for red squirrels, but not greys, are one possible option. Owing to the difficulty of avoiding unintended deaths of red squirrels, grey squirrel control using anticoagulant poison may not be undertaken where reds still occur. Trapping or shooting are possible control options, but are costly and difficult to implement over large areas.

Long term habitat management offers promise, particularly in plantation forestry. Removal of broadleaved trees deprives grey squirrels of preferred foods. Conifers can be managed to provide Optimum conditions for reds by diversifying the species planted. The planting/felling cycle should be managed so that two thirds of the total area of conifers is of seed producing age, with half the trees being more than 30 years old (Gurnell & Pepper, 1991). However, this type of management may conflict with economic objectives.

Suggested prescription for conservation management for the red squirrel: 1. Suppress or remove grey squirrels, especially in deciduous woodland.

2. Encourage species diversity among conifers used in plantation forestry.

3. Lengthen the felling cycle in plantations to 50 years or more, to ensure good cone crops on mature trees.

4. Maintain a continuous canopy to aid arboreal activity.

5. Ensure arboreal links are maintained between woodlands.

6. Supply supplementary food and perhaps nestboxes.

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External Factors The red squirrel shares several ecological traits with the dormouse. Both are arboreal feeders, both have a fine pelage poorly suited to repelling rain and both are likely to be disadvantaged in our moist maritime climate, particularly in windy conditions. It has been shown that the dormouse is threatened by the instability of the British climate (Bright & Morris, in press). Cold or wet weather significantly curtails nocturnal activity (Bright, Morris & Wiles, in press) and bad weather delays ripening of key foods (and is also likely to reduce food quality). The dormouse has declined particularly in northern counties where the climate is least propitious. It is notable that it is now restricted to a very few localities in Suffolk and absent from Norfolk. This also corresponds to the fact that the mean summer temperatures of Suffolk are higher than for Norfolk (Meteorological Office, 1952). Climate management is not an available conservation option, consequently it becomes even more important to ensure best practice in habitat management in counties such as Suffolk where the dormouse is living at the edge of its climatic ränge. Where the climate is less challenging, sub-optimal habitat may still support dormice. The red squirrel may also be adversely affected by the British climate, being better adapted to drier Continental conditions, but experimental evidence is currently lacking.

The wider countryside Conservation management of these two species in particular highlights a key issue: management within protected sites does not occur in a vacuum, but must take account of circumstances beyond their boundaries. Woodlands are increasingly becoming isolated islands of habitat surrounded by areas of open (often hostile) land. The mammals that live within them are thus inhabiting terrestrial "islands", which may be too small to support a viable population of key species (Bright, 1993). Studies of oceanic islands demonstrated that small size leads to chance extinctions and remoteness inhibits recolonisation. Thus, the smaller and more isolated an island is, the more species it will lose to extinction (MacArthur & Wilson, 1967). The same is true of woodlands. If the strongly arboreal dormice die out in a small wood, they are relatively unlikely to cross open fields to reinvade. Extinction will then be permanent. This is why connecting hedgerows are likely to be important where woodlands are reduced to small patches.

Many woodland nature reserves are small, but how small is too small?

A survey in Herefordshire (Bright, Mitchell & Morris, 1994) suggested that isolated woods smaller than 20ha were likely to lose their dormice in the course of time. Woods isolated by more than 1km were unlikely to be recolonised.

Dormice often occur in smaller patches of habitat, but their future is uncertain, especially where habitat quality is poor. The red squirrel is also disadvantaged by habitat fragmentation, highlighted by a study in Lancashire (Bright, unpublished) which revealed that woods more than 5km distant from a major red squirrel nucleus were unlikely to have squirrels present. The implication is that large areas of contiguous red squirrel habitat are very important to this species and should be identified as key conservation sites. The minimum area needed to sustain red squirrels is not known. Holm (1990) found immigration and emigration to be frequent among squirrels inhabiting small (2-4ha) copses, with more stability in woods exceeding 20ha.

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Reintroductions Reintroduction is proposed for red squirrels probably more often than for any other species and a full-scale reintroduction was attempted in Regent's Park, London in 1984 (Bertram & Moltu, 1986). It was unsuccessful. Such projects are futile unless the problems associated with habitat quality and competition from grey squirrels are first resolved. Moreover, capture of squirrels or dormice for translocation depletes populations that are already rare. A particular problem with the red squirrel is that it is easily stressed and reacts badly to capture and transport. For these reasons, captive bred stock may be a more desirable source of animals, but it is unclear how (or even whether) such animals can cope with release into the wild. It also be necessary to breed substantial numbers in order to release a viable population nucleus, but red squirrels are not often bred in captivity at present. Trial translocations of the dormouse have been carried out (Bright & Morris, 1994) and may prove a viable conservation option, using captive bred individuals and those rescued from the path of road developments. Recent attempts have been made to re-establish dormice in Cambridgeshire and Nottinghamshire, using captive bred animals. The populations have persisted at both sites, with successful breeding, for at least two years.

Conclusions Many of the management themes discussed here also apply to other species.

The dormouse and red squirrel are Flagship Species, high profile animals whose conservation will also result in support for a wide diversity of other less charismatic creatures, and maintain aesthetically pleasing habitat at the same time. Management aimed more at bird or insect diversity may often also benefit mammals. For example, leaving dead wood (for insects and fungi) provides dormice with nest holes and sheltered sites for hibernacula.

Woodlands are too diverse for universal application of a Standard management plan. The management prescriptions proposed above are highly simplistic and need to be interpreted in relation to local circumstances. They also help to highlight the need for clarifying objectives and priorities, something which is frequently overlooked in woodland management where attempts often aim at trying to conserve everything, on sites that are too small.

Permissive management of the surroundings should also be considered as part of woodland management, especially in respect of hedges and the potential for planting trees and hedges to link copses. Vigilance is needed to avoid destruction of woodland Connectivity. Where destructive actions occur, such as road widening, species-rich hedges should be replanted to 'sew together' remnants. Management should be infrequent and low key to enable fĂźll development of the hedgerow shrubs and the fauna they support..

Conservation, particularly of dormice and red squirrels helpfully highlights the fact that conservation strategies cannot be based on site management alone, but must take account of the wider countryside and broader issues (e.g. land use policies or public acceptability of culling pest species). Indeed, few British mammals are as habitat specific as the dormouse and red squirrel, and even these require a wider perspective in habitat management. The future of most species will very much depend even more on a broader approach to conservation management.

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P. A. Morris, School of Biological Sciences, Royal Holloway, University of London TW20 OEX

Trans. Suffolk Nat. Soc. 32 (1996)

Plate 1: Dormouse, Muscardinus avellanarius L., a scarce species in Suffolk with a preference for ancient semi-natural, coppiced woodland (p. 151).