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Action for Scotland's Biodiversity

6 FORESTS AND WOODLANDS

Introduction

Scotland's remaining native pinewoods provide a living link with the past, as here at Abernethy Forest

"These woodlands are of great interest, and not only to the specialist. Even to walk through the larger of them gives one a better idea of what a primeval forest was like than can be got from any other woodland scene in Britain. The trees range in age up to 300 years in some instances, and there are thus not very many generations between their earliest predecessors about 9,000 years ago and those growing today; to stand in them is to feel the past". This quotation from Steven and Carlisle's The Native Pinewoods of Scotland indicates that a large part of Scotland was once covered by the trees of the Old Wood of Caledon, or the Caledonian Forest. Sadly, most of this ancient forest has disappeared, although parts of it still survive in what can now only be described as semi-natural woodland areas. Other parts have been encouraged to regenerate or have been replanted - though sometimes with a range of different species.

Out of a current total forest area of about 1,300,000 ha it is estimated that the total area of semi-natural forest is less than 200,000 ha. Nearly 90 per cent of it is in the Scottish Highlands, i.e. north of the Highland Boundary Fault and to the west of the eastern edge of the Grampian mountains. In terms of biodiversity most of these areas are intrinsically very important, but some are unique due largely to their relative isolation from mainland Europe and the strong oceanic influences of the north Atlantic

Most of the other woodlands in Scotland are plantations, in which the present landowners and their predecessors will have invested deliberately, either to provide timber or shelter, or to improve the amenity of the rest of the estate. Some of these plantations are on land where previously there had been no trees for centuries, and a number of non-native species will have been used. This is particularly true of the plantations established over the last 80 years or so, in accordance with successive governments' afforestation policies. In general, these plantations (about 70 per cent of the current total forest area) will need to be managed rather differently in order to develop their biodiversity potential; this gradual process has already begun.

Woodland Ecosystems

In the ancient forest, oak or Scots pine would probably have been the predominant species, though depending on local soil and climate it could have been ash, birch or alder. The woodland's structural development was a natural process influenced on the one hand by the mutual competition between different plant species to regenerate and grow, and on the other by the effects of fungi, sap sucking and defoliating insects, seed-eating birds and small mammals, the more destructive effects of the larger herbivores and the occasional catastrophic event such as a storm, heavy snow or fire caused by lightning.

This process was often adversely affected by human interference which has persisted to the present day. The forest was exploited for its timber and other products, and the land was cleared in order to grow other crops or to provide pasture for domestic animals, and more recently to make way for other developments. The continuity of forest cover was broken, remaining only in the more inaccessible and relatively remote areas.

Partly as a result of this fragmentation it is easier now to identify the component woodland types of the original forest, and to think of them as different habitats rather than as a continuum of habitats gradually changing from one to another. Many of them have the following features in common, namely

• individual areas are generally small;
• regeneration is poor or absent, with a depleted shrub and ground vegetation layer, usually due to heavy browsing by deer and sheep;
• deliberately introduced non-native species are present, and the woodlands are affected by the spread of invasive species;
• they have poor age-class structure, i.e. a disproportionately large amount of older and senescent trees which are less capable (infrequent production of less viable seed) of regeneration, thus jeopardising the future existence of the individual woodland; and
• the habitat value is compromised (thus the characteristic species are those least able to adapt to more open or changing conditions, or to move between the 'retreating' woodland blocks, and many species are declining in abundance, with gene flow also at risk as the population sizes dip below critical levels).

Native Pine Woodlands

The native pinewoods of Scotland are the westernmost representatives of the European Boreal forest. The principal species is the Scots pine but, depending on the location, soils and climate, there may also be some birch, rowan, juniper, alder, willow, aspen, and even oak present. There are extensive pinewoods in Strathspey, Deeside and in the Beauly catchment; at the other extreme there are some pinewood remnants elsewhere in which there are only a few very old trees, and regeneration is virtually non-existent. Using biochemical analysis techniques we can identify seven separate pinewood groups, of which the north-west group (centred on Shieldaig) is the most distinctive; it is least like any of the other groups which show more affinity with pines from central Europe.

Some of the rarest priority species are only found in pinewoods, for example the Scottish crossbill and the Caledonian sac spider. There are, however, also other species like capercaillie and twinflower which prefer pinewoods as a habitat, though they seem able to survive in other woodlands.

Capercaillie are heavily dependent on native pinewoods	Native pinewoods also support several characteristic plant species such as twinflower

Upland Oakwood

Upland oakwoods consist mainly of oak, usually sessile oak though pedunculate oak can be locally common, particularly in the east. Mixtures of both species and hybrids can occur. There are significant areas of upland oakwoods in Wester Ross, Lochaber, Argyll, Deeside, Perthshire, Stirlingshire and Galloway. Birch is a major component of many of them, and is occasionally dominant, usually due to earlier exploitation of the oak for its timber and tannins or to the prevention of oak regeneration due to browsing by sheep and deer.

Oakwoods grow on a variety of soil types; these affect the diversity and composition of the ground vegetation. Under the trees the ground flora varies from a mixture of bluebell, bramble and ferns, through grass and bracken stands, to moss-dominated areas. The latter are the so-called 'Atlantic oakwoods', which occur along the west coast and are some of the richest habitats for mosses, liverworts and lichens. Oakwoods in general are also good for invertebrates, and in Scotland the more open oak/birch woodlands in the Great Glen are now major strongholds for butterflies like the pearl-bordered fritillary and the chequered skipper.

Oakwoods in western Scotland support an exceptional range of mosses, liverworts and lichens	Careful grazing management is needed for butterflies such as the chequered skipper

Upland Mixed Ashwoods

The range of the upland mixed ashwoods is very similar to that of upland oakwoods, also occurring on sites which are only just above sea level in the north-west Highlands. Where the two woodland types merge together within any one woodland the ash is usually found on the damper base rich soils. Ash is also relatively quicker to colonise any suitable open ground along the woodland margins. Other component tree species may include elm, birch, alder and willow, and the shrub layer frequently contains hazel, especially in west Scotland, and possibly hawthorn.

The rare lichen Arthothelium macounii is a species which occurs in ashwoods, but also on smooth barked hazel trees in Atlantic oakwoods. It is an example of a species whose requirements have rather more to do with the conditions of light, humidity and long ecological continuity than simply the woodland type.

Wet Woodlands

Wet woodlands are usually dominated by alder, willows and birch and occur on poorly drained or seasonally wet soils. They are often transitional woodland types which intergrade with all of the other woodland types discussed here, as well as with other (non-woodland) wetlands. The soils of wet woods can vary from infertile peats to nutrient-rich mineral soils and the ground vegetation varies tremendously depending upon the type of wet woodland. In areas where the aspen grows, the rare hoverfly Hammerschmidtia ferruginea might also occur (Box 6.5).

Wood pastures such as this at Dalkeith provide an open structure which is important for a range of specialised plant and animal species

Lowland Wood-pasture and Parkland

Lowland wood-pastures are a particular form of managed native woodland. They are rare in Scotland, but particularly fine examples occur at Dalkeith and Cadzow (Hamilton). In their original working condition, the trees would be very widely spaced, and grazing (usually by domestic animals) would be allowed at a level which would maintain the features of the site. The open structure of the woodland, coupled with the presence of veteran trees, is important in supporting a large number of scarce fungi, lichens, bryophytes and invertebrates, especially those associated with dead wood. One of these is Bacidia incompta, a crustose lichen which grows on the trunks of mature trees like elm, but is also known on ash, beech, holly and sycamore. Birds like the spotted flycatcher and tree sparrow favour this type of habitat.

Birchwoods

At least one third of all the semi-natural woodlands in Scotland are birchwoods, where the predominant species is silver birch or downy birch. As young woods they can be the natural successional stages of other woodland types, especially pinewoods and oakwoods. The longer lived pine or oak gradually re-assert themselves as the dominant species, unless prevented by factors such as heavy browsing pressure. In other places, some older birchwoods may be all that remains of these other woodland types since the principal (and more valuable) species have been removed, and are not 'seeding in' because local seed sources have largely been removed or are absent. This situation has prevailed for decades in many cases; hence the dominance of birchwoods in Scotland.

Compared with oaks and willows in Scotland, birchwoods are relatively more important for invertebrates. This is because some of the plant feeding insects and mites which seem to prefer oaks and willows in the south of England do not occur in the north. Other species are predominantly restricted to birchwoods. An example, but one that does not have a Species Action Plan, is the Kentish glory moth, now confined in the UK to Speyside and Deeside. This unusual moth will lay its eggs only on birches below 3 m in height, and hence it only occurs within extensive areas of regenerating birch.

Action Plans

The native woodland habitat action plans set out what needs to be done to address the problems of woodland biodiversity. They contain a number of quantified targets, with deadlines for their completion, and a list of complementary actions. Implementing them does not mean trying to re-create some vision of the past wildwood, or the landscape at a particular point in historical time; rather, we should learn from our knowledge of the past and consider how to work with natural processes in constructing our vision for the future. In all cases the targets involve

• protecting semi-natural woodland from further destruction, misuse or neglect;
• improving the condition of the woodlands and enhancing their conservation status, so that they become fully functioning ecosystems again, where the regeneration of the main tree species and the characteristic shrub and herb layers is not inhibited;
• restoring those woodlands which have been adversely affected by the introduction of non-native species; and
• reversing the effects of fragmentation by enlarging the woodlands, preferably by natural regeneration on to adjacent sites, or establishing new woodlands of native species, including restocking former ancient woodland sites after the removal of exotic conifers.

Many of the listed actions are generic, and apply to all the native woodland plans. These include encouraging more positive discrimination within land use policies and regulatory procedures; better targeting of incentive schemes; undertaking more research to improve understanding of the biological consequences of various management options; providing technical guidance and advice to practitioners, and supporting this with better training; as well as developing better decision support systems and monitoring techniques. There are, however, some actions which only apply to specific plans. Examples would be

• for pine woodlands, updating the Caledonian Pinewood Inventory;
• for wet woodlands, identifying four large scale sites for the creation of flood-plain forests in the UK; and
• for lowland wood-pasture, establishing grazing regimes in derelict wood pastures in order to rehabilitate them.

Some of the Challenges

Putting these actions into practice involves a whole range of tasks, some of which are major challenges in themselves, requiring technical and advisory support and, of course, funding. This can be demonstrated by four examples.

First, there is woodland protection. As uncontrolled browsing by deer and domestic animals is a key factor, one could simply try to ensure that the woodlands and any regeneration is securely fenced off. However, deer fencing is a major cause of capercaillie and black grouse death, through 'birdstrikes'. The alternative options include making the fences more clearly visible to the birds, siting the fences more carefully, or trying to control the deer by other means so that fences are not required at all and ensuring that all redundant fences be removed. Allowing a limited amount of grazing within the woodlands can partly control the 'scrubbing over' of the natural open spaces; this will help some woodland butterflies, like the pearl bordered fritillary, which feed on the nectar of woodland flowers. Herbivores are, after all, a natural part of woodland ecosystems.

Second, woodland improvement is important. Removing invasive species like rhododendron is unlikely to be satisfactorily achieved in one 'go', especially if there are residual seed sources in the soil nearby. Ideally, one requires a co-ordinated control strategy for a discrete area like a glen, or a water catchment isolated by bare hills, or even a single woodland estate surrounded by agricultural land devoid of rhododendron. Control has to be directed at all of the rhododendron in the area, not just at what is in the native woodlands. This needs co-operation between neighbouring owners and probably a jointly funded approach. Successful removal of non-native species such as exotic conifers is relatively easier, but raises questions over the optimum timing and the owners' prerogative to manage their woodlands for other objectives.

Third, woodland expansion needs to be considered. Simply calling for native woodland expansion raises a number of questions. Where might it be done to best advantage, both within a locality and across Scotland as a whole? Should equal weight be given to all woodland types in all areas, or should the status of any one or more priority species influence that weighting? What relative priority should be given to other habitats? Should the process be left to chance, basically accepting what happens, or should it be directed, usually with some targeted incentive? This is where the concept of Forest Habitat Networks is useful because it aims to show where woodland expansion might make optimum use of the land which is likely to be developed as woodland.

Finally, there is a need to benefit all woodland species. Underpinning this effort is the assumption that the woodlands will once again meet the habitat needs of the dependent species, especially those that are currently endangered through the historical reduction or destruction of their habitat. This habitat based approach highlights the urgent need for further research to clarify individual species' requirements, such as the reasons for scarcity or sensitivity, critical habitat conditions, dispersal and recovery potentials, and minimum viable areas. Such research might identify what are the common factors, or alternatively where there may be conflicts between species' requirements. Enlarging existing woods, or re-connecting them as part of a habitat network, is likely to assist the less mobile species to spread more freely. An increase in the area of forest will also help larger animals which need to range over larger areas.

Progress at the Start of the 21st Century

Interest in the biodiversity of native woodlands in Scotland has been building up for many years, not least since the publication of The Native Pinewoods of Scotland (quoted at the beginning of this chapter). A number of initiatives are in place which pre-date the publication of the Habitat Action Plans. These plans have, however, been the catalyst which have renewed the momentum and given it structure. Already there is a number of positive outcomes, only a few of which are mentioned here.

More resources have been applied to native woodlands. The Forestry Commission's Woodland Grant Scheme has been extended to offer discretionary funding for improving woodland biodiversity. There have been woodland expansion Challenge Funds to encourage the planting of native trees in the Forest of Strathspey and the Deeside Forest. European LIFE funding has also been used to good effect, all involving woodland restoration, for example in the Caledonian pinewoods (mostly in Glen Affric), in the Atlantic oakwood Special Areas of Conservation (near Loch Sunart and elsewhere), and in wet woodlands in a number of different areas in the Highlands. Further south, as part of the larger Millennium Forest for Scotland Project, the MoD has embarked on the regeneration of oakwood at Garelochhead.

Macaulay Land Use Research Institute and Scottish Natural Heritage have developed and refined their concepts of woodland modelling and Forest Habitat Networks into practical decision support systems. These will help woodland managers to decide where the best places for woodland expansion are located.

Woodland owners, including Forest Enterprise, consider that they are on course to meet the action plan targets. In purely quantitative terms, the pinewood expansion target has been exceeded already, but it is worth reviewing how well the location and scale of what has taken place meet the qualitative criteria of the native pinewoods plan. It is still too early to assess the degree to which the majority of woodland priority species, shown in Box 6.1, is being conserved.

Woodlands are excellent places to learn about the variety of wildlife	Native woodland restoration and expansion is taking place in several areas, particularly in the Highlands

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