Montane Scrub
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Montane Scrub Natural Heritage Management MONTANE SCRUB ACTION GROUP SCOTTISH NATURAL HERITAGE Scottish Natural Heritage 2000 ISBN 1 85397 103 0 A CIP record is held at the British Library L2K1100 Acknowledgements Authors: Michael Scott for the Montane Scrub Action Group This booklet is an output from the Montane Scrub Restoration Project part of the Millennium Forest for Scotland managed by Highland Birchwoods, and has been endorsed by the Royal Society for the Protection of Birds. Photography: D. Bell/Ecos 22, M.Biancarelli/Woodfall Wild Images 15 bottom right, L.Campbell front cover bottom right, 13, 15 bottom left, A. Hester front cover left, 2 bottom, 20, 31right, D.Gilbert 19 centre, L.Gill frontspiece, 2 top, 4 top, 4 centre, 4 bottom, 7 top, 7 bottom, 8 top, 8 bottom left, 8 bottom right, 9 top, 9 bottom, 10 top, 10 bottom, 11 top left, 11 top centre, 16 top, 16 bottom, 19 top, 23 bottom, 27, 31 left, D.K. Mardon front cover top right, 12, 14, 15 top right, 17, 21 top, 21 bottom, 23 top, 24, 25 top, 25 bottom, 29 left, 29 right, 30, R.Parks 11 top right, K.Ringland 15 top left, R.Soutar 19 bottom, M.Scott 3, 6, 26 top, 26 bottom, 28. Illustration: C.Hewitt Further copies of this booklet and other publications can be obtained from: The Publications Section, Scottish Natural Heritage, Cover images: Battleby, Redgorton, Craig Fhiaclach (left), net-leaved willow (top right), black grouse (bottom right). Perth PH1 3EW Tel: 01783 444177 Fax: 01783 827411 Back page image: Cliff flora with net-leaved willow, Ben Lawers. MONTANE SCRUB Preasarnach na beinne Foreword Over the last 15 years we have reversed the threat to our native forests The Forestry Commission’s role is to maximise the environmental and and woodlands and the process of restoration and expansion is well social benefits of forests as well as ensuring that they continue to underway. However, at the upper margins of our forests, one woodland produce a flow of timber to support the rural economy. We have been type, depleted more than most, has yet to be tackled. Remnants of at the forefront of the restoration of Scotland’s native woodlands both montane scrub have hung on as trees or clumps of trees in exposed in our own forests managed by the Forest Enterprise and on land and remote locations, often protected from grazing animals by terrain. owned privately, supported through our Woodland Grant Scheme. They are all that’s left of a once widespread zone between the forest and the open moorland. We enthusiastically support the current interest in treeline woodlands; they are an important element of the Forest Habitat Network approach These remnants are invariably cut off from the forests they once fringed which is a priority action in the Scottish Forestry Strategy. The restoration and no longer function within an extensive ecosystem. The contorted process will not always be easy, nor indeed achievable everywhere. shapes and diminutive habit that we associate with montane scrub is However, where it can be done the rewards will be very visible and no accident. The trees survive in the most hostile conditions above tangible. As the trees move up the hills they will not only enhance this the slopes where foresters have traditionally planted and regenerated landscape and our natural forest biodiversity but will establish the trees. So the restoration will be a slow but rewarding process as a missing element in our vision of a continuum of woodland cover from diffuse boundary evolves between forest and mountain. the river valleys to the biological limit of tree growth. Sir Peter Hutchison Chairman Forestry Commission Contents Introduction 2 Shelter on the hill 21 What is montane scrub 3 Game benefits 23 The loss of the ‘wee trees’ 7 Enjoying the hills 24 Plants of the scrub 10 Ecological values 25 Wildlife in the scrub 13 Action for scrub 27 Restoring the landscape 17 Bringing back the ‘wee trees’ 30 The woods and the trees 19 Further reading 31 1 Introduction "The gnarly little trees were twisted as if cultivated by That, however, overlooks the special qualities of montane scrub as a deranged bonsai gardeners...Thus the name krummholz, natural fringe to the forest. This booklet is a celebration of this forgotten German for 'crooked wood' or perhaps 'elfin wood' - the zone montane scrub habitat. It illustrates its value as a home or corridor where trees first managed to take advantage of the soil- for plants and wildlife; as shelter for domestic stock and forestry; as building work of fellfields and alpine meadows. Treelimit." a valuable resource in its own right; and as an attractive part of Scotland's natural heritage. (’Green Mars’, Kim Stanley Robinson) These gnarled, twisted trees - and the rich diversity of other plants and animals associated with them - are not just a product of the tundra or the Alps. They once occurred on Scottish mountains as a natural zone between woodlands and hilltop heaths. But this montane scrub has almost disappeared from Scotland. In conservation terms, it is one of our most significant 'Cinderella' habitats. In recent years, people have come to realise how much the natural vegetation of the Scottish uplands has been impoverished by human activities. In response, an encouraging start has been made to restoring some of the woodland that once covered the straths and glens and spread up the hillsides beyond. Whether for environmental ends or for commercial forestry, most of this work has been driven by the desire to grow tall, straight trees. It has usually stopped at the altitude above which foresters believe trees will not grow. 2 What is montane scrub ? Trees can grow in the most unpromising situations. Their roots spread This view from Sweden gives an impression of how some parts of the out to find nourishment and water, and act as an efficient anchor and Scottish hills might look if the first tentative steps to restore Scotland's prop, supporting the tree against the battering of gales. But no trees montane scrub can be successfully expanded to a larger scale. can grow near the tops of Scotland's highest mountains. As trees approach their altitudinal limits, their growth is severely It is simply too windy and exposed, and the growing season is too retarded by long periods of low temperature. Pruning by icy winds short for trees to establish. A range of 'dwarf shrubs' are the only woody makes their branches grow outwards, rather than upwards. The result plants that can survive at these altitudes. They include ling heather is low-growing, crooked trees. Their twisted timber is of little value to (Calluna vulgaris), crowberry (Empetrum nigrum), bilberry or blaeberry traditional forest industries, so foresters avoid planting trees here. (Vaccinium myrtillus), bog bilberry (V. uliginosum) and other, more localised species. Even at lower altitudes, the forest does not consist solely of tall forest trees like sessile oak (Quercus petraea), downy birch (Betula pubescens) What happens between the woodland zone on the lower slopes and and Scots pine (Pinus sylvestris). Mixed with them are lower-growing, the dwarf shrubs high on the hill? It is wrong to imagine that there is more shrubby species, such as rowan (Sorbus aucuparia), juniper a precise altitude at which tree growth is no longer possible and the (Juniperus communis) and willows (Salix species). As the high forest forest simply ends. Trees can creep higher where a gully offers shelter trees begin to decline towards their altitudinal limit, these smaller than they can on a wind-exposed hillside, so the upper margin of the species become more prevalent and eventually replace them completely forest is naturally 'feathered'. Straight upper edges of forests arise only at altitudes above which the forest trees can no longer survive. Some where fences to exclude grazing animals are constructed insensitively. shrubby species are high altitude specialists (see page 4), although several of these are now rare in Scotland. 3 There is, therefore, a zonation up the hillside (see figure 1), although the gradation from one zone to the next is gradual, with indistinct boundaries. The forest zone is the extensive area at low altitude in which trees grow tall and upright, and generally produce good timber. MONTANE HEATH MONTANE At a particular altitude (which will vary with climate and exposure), trees can no longer maintain this upright growth form. That marks the timberline. Some trees may survive for a hundred metres or more above this altitude, but they grow progressively shorter and more twisted. Continental botanists call this zone ‘krummholz’, which means literally 'twisted wood'. Then an altitude is reached at which the climate becomes so severe that even krummholz can no longer survive. This is the treeline. MONTANE SCRUB MONTANE Specialist montane scrub species Dwarf juniper (Juniperus communis nana) Dwarf birch (Betula nana) * Montane willows:- Mountain willow (Salix arbuscula) * Dwarf willow (S. herbacea) Woolly willow (S. lanata) ** Downy willow (S. lapponum) * Dark-leaved willow (S. myrsinifolia) Whortle-leaved willow (S. myrsinites)* Tea-leaved willow (S. phylicifolia) FOREST Net-leaved willow (S. reticulata) * **rare ("Red Data Book") species * scarce species Figure 1: An idealised zonation up a mountain as the trees of the forest zone are replaced by low-growing scrub including stunted, twisted plants of Scots pine and then by dwarf shrubs on the high tops. A slightly different terminology is used on the continent (right hand column). Legend: Tree species (mainly Scots pine and birch) BRITISH TERMINOLOGY TERMINOLOGY CONTINENTAL Montane scrub species (mainly juniper and willows); In Scotland these can occur throughout the range, becoming patchily dominant above the natural treeline.