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Action for Scotland's Biodiversity

8 SPECIES WITHOUT 'PIGEONHOLES'

Introduction

Action Plans have been prepared for species which are globally threatened or are declining rapidly in the UK. The selection of the Habitat Action Plans listed in Annex 2 are perceived as particular priorities for conservation action. Many of the species listed in Annex 3 fit comfortably into these priority habitats. It is, however, inevitable that some of the species selected for priority action do not fit conveniently into the 'pigeonholes' of the Habitat Action Plans or even of the broader Habitat Statements. Some of these species, such as the pipistrelle, occur in a very wide variety of habitats, whilst others, such as the Shetland mouse-ear, are associated with very specialised habitats (Box 8.1).

Some species, such as the pipistrelle bat, occur in a very wide variety of habitats

Transitional Habitats

Perhaps the most conspicuous gap in the suite of Habitat Action Plans is for habitats which are essentially transitional in nature. These once would have occurred at the transition between two broader habitat zones, or in situations where environmental conditions were highly unstable. Today, with so much of the landscape 'tamed' and 'controlled', they are most likely to survive as the product of particular management activities. Indeed, it is difficult to see how the Habitat Action Plan process could contribute easily to habitats that are essentially transitional or transitory in nature.

One significant 'missing' habitat in this category is lowland scrub, which occurs as a transitional zone between high woodland and various open habitats as a result of altitude, exposure, past fires or past felling. Young's helleborine (Box 8.2) would appear to be best categorised as a species of such scrub, although it could equally be argued that it is a species of industrial environments created by human activity (it is only recorded on old pit bings that have been colonised by scrubby woodland). The key lesson from this species is the need for biodiversity actions to maintain the natural dynamics of plant and animal communities, both for the benefits of species associated with these natural transition zones and because the process of dynamic change is itself a component of biodiversity.

Species of these transitional habitats include Young's helleborine (Box 8.2) and the small weevil Melanapion minimum, which used to be found in Dumfriesshire and Kirkcudbrightshire. It now occurs rarely in England and Wales on willow species in woodland, on the margins of woods, along the sides of ponds, river and other watercourses, and in carr. The plan for this species relies upon trying to relocate this small beetle in Scotland, and to consider re-introducing it to appropriate sites within its former range.

Young's helleborine is a rare orchid found only on a few disused bings in Scotland

Species of Mosaic Habitats

Another group of priority species require not a single habitat, but an intimate mixture of habitats in close proximity to one another -what is called a 'habitat mosaic' or 'habitat matrix'. The black grouse, for example, is a species which breeds and rests in coniferous woodland but moves out into open heathland to feed (see Chapters 6 and 7). It can therefore be categorised as a 'woodland edge' species, dependent on the habitats on either side of this boundary. Its future well-being must be the responsibility of both woodland managers and those that manage adjacent open habitats. A sectoral approach to countryside management can be one of the factors which puts species under pressure. This mosaic of habitats is essential for a number of other species, such as the great crested newt and a number of farmland and woodland birds.

Two of the mosses listed in Box 8.1 have unusual habitats that could be considered either as mosaics or as transitory in nature. The cernuous bryum grows in patches of damp soil, often beside streams, but sometimes in coastal dune slacks. It has, however, not been seen growing in the UK since 1970. The spreading-leaved beardless-moss grows on moist, exposed, non-calcareous clay, loam and mud in lowland fields, beside ditches and pools, and in woodland rides. There are very few post-1950 records of this species. The Species Statements for these two species are targeted at re-surveying sites where the species were formerly recorded; if the species are re-discovered, then it will be appropriate to develop the Statements into Action Plans.

The pipistrelle bat is another species that requires a mosaic of habitats. Although still a widespread and abundant species (or pair of species; there is still taxonomic doubt), it is thought to have declined significantly over the last century. The action plan objectives are to maintain the existing population size and range of the species, and to restore the populations to the pre-1970 numbers. For this species, it is seen as essential to provide more information so that the public appreciates the importance of bats. The actions are listed in Box 8.3.

All of these species have complex requirements, and their future well-being will depend, like the overall biodiversity process, on a wide range of players. It is not possible to draw out a group of actions for one particular group of land managers that will have a beneficial effect on the future of these 'species without pigeonholes'. Rather it would seem that the overall requirement is for a diverse landscape with small-scale patches of varying habitats -something, in fact, much closer to the natural mosaic that was once the norm in many parts of Scotland. The challenge of balancing that with the needs of human communities is no easy task, but it is essentially one of policy and planning, for which the greatest weight of responsibility must lie with central Government and the Local Biodiversity Action Plans. Perhaps the key lesson is that 'blanket anything' is unnatural in the environment and bad for biodiversity! This is true whether it is blanket forestry, blanket agriculture, blanket development, blanket urbanisation - or possibly even blanket conservation!

'Individualistic' Species

That still leaves five purely 'individualistic' species in Box 8.1 for which no overall generalisations can be made. In most cases these belong to very precise and restricted habitats which do not fit conveniently into any of the habitats covered by Habitat Action Plans.

The weevil Ceutorhynchus insularis is only known from two islands, one off Iceland and the other Dun, in the St. Kilda archipelago, and only 13 specimens have ever been found! The weevil's larva is said to eat common scurvygrass leaves in these coastal situations, but, being so rare, little is known of its ecology.

The island of Dun, in the St Kilda group, is one of only two known sites in the world for a rare weevil	Shetland mouse-ear's world distribution is the island of Unst, Shetland	An astonishing 14 types of hawkweed have been identified on a variety of sites in Shetland: they are the Scottish equivalent of Darwin's finches or the Hawaian fruit flies

The Pict-moss has only once ever been found, growing on a small, isolated tree, possibly a rowan, on a dry limestone outcrop near Glen Shee. Until further specimens are discovered, nothing is known about the ecology of this species. There is also some taxonomic doubt as to whether or not it is a distinct species.

Another of these species is the Shetland mouse-ear, an attractive, tufted plant related to the garden snow-in-summer and with equally handsome flowers. It is found exclusively on the island of Unst in Shetland in a habitat so unlike anything else in Scotland that it could almost be the surface of Mars! It is an area of 'debris' of serpentine rock; this is so toxic to most species that 90 per cent of the area is a bare 'clitter' of shattered stone without any plants. The Shetland mouse-ear has extremely precise requirements of soil, exposure and management. Fortunately its future seems relatively secure within a National Nature Reserve which is also a Site of Special Scientific Interest. However, it is likely to be highly susceptible to the effects of climate change and may, indeed, be a species that would repay monitoring, as a 'miner's canary', to give advance warning of the impact of climate change.

Also found on Shetland is a group of hawkweeds in a small section of the genus Hieracium. Many plants in this genus reproduce by a process of inbreeding called 'apomixis'; this tends to give rise to clusters of 'microspecies' that are very similar to each other but just slightly different from other 'microspecies'. The Shetland plants (which represent 14 'microspecies') are found in a range of locations, including coastal rocks, dry heaths, pastures, meadows, streamsides, sea-banks, sea-cliffs, granite cliffs and limestone ravines. Yet across this range of habitats, the management requirements of the hawkweeds are more similar to the requirements of their close relatives than to the requirements of other species that share these habitats. Again, they are best regarded as 'individualists' which cannot be conveniently grouped for management purposes with other Species Action Plans. However, they are a significant part of Shetland's unique natural heritage which merits a special place in the land management priorities for these islands. They are the Scottish equivalent of Charles Darwin's Galapagos finches or of the astonishing variety of Drosophila (fruit) flies on Hawaii.

Spruce's bristle-moss has only once been recorded in Scotland, in Stirlingshire. It is epiphytic on the bark of trees within flood-zones of streams and rivers. However, it is exacting, and it grows at levels that remain dry for much of the year but which are inundated at times of flood. The main action in Scotland is to determine the exact locality or localities where the species occurs, and then to protect, and possibly supplement, the host trees, although river management clearly will have a significant role to play in ensuring its exacting requirements. Another species of unusual wet habitats is the Irish lady's-tresses. Details of this are given in Box 8.4.

Conclusions

As this and the preceding chapters have shown, a number of Species Action Plans share many common requirements, which can conveniently and cost-effectively be addressed within the scope of the broader Habitat Action Plans. Yet the 'ragbag' of 'species without pigeonholes' in this chapter emphasises that individual species also have their own idiosyncracies and distinctive requirements. We must ensure that we do not lose these within the habitat groupings. Many pinewood species, for example, share common problems as shown in Chapter 6, yet they may also have individual requirements. Management prescriptions that are in the best interests of the overall pinewood habitat may not necessarily be to the benefit of every denizen of that habitat. There is a need for a balance between the demands of Habitat Action Plans and the demands of a number of Species Action Plans. The greatest strength of the Biodiversity Action Plan process is that it aims to encompass both the communal requirements of habitats and the individual requirements of species in a holistic programme for the future of the priority components of Scotland's cherished natural heritage.

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