Information and Advisory Note Number 26 Back to menu
1.1 There has been a general awakening of awareness of the conservation
importance of the British uplands in a European context in recent years. This has
highlighted the need to clarify different terminology in use, here and on the
Continent, for comparative purposes. Furthermore, the EC Habitats Directive
(1992) has introduced a number of Continental terms into usage whose meaning
requires clarification in relation to the British uplands
1.2 This Information and Advisory Note provides guidance on terms and on the most appropriate terminology to use for the uplands m relation to.
Information and Advisory Note 56 will provide summary details on National
Vegetation Classification communities in the uplands
1.3 SNH and Ratcliffe and Thompson (1988) define the uplands as lying 'typically above the limits of enclosed farmland', i e. above the head dyke or fell wall. Others treat the uplands as 'lower hill country', including the enclosed ground of the upland fringes, and hence refer to uplands and mountains as separate zones. The English Nature definition of the uplands is land within 'Less Favoured Areas' which takes in lower hill country,' including enclosed hill farmland, and mountains.
2 1 Vegetation on mountains shows an altitudinal zonation in response to an
increasing seventy of climate (Fig 1). Conditions become progressively harsher
with an increase in altitude due to a decrease in temperature, and increases in
wind-speed, precipitation and snow cover. In natural conditions, forests cover
the lower slopes. Higher up, tree growth becomes progressively shorter until
there are only scattered, stunted individuals. The upper limit of tree growth
forms the lower limit of the alpine zone. This upper limit of tree growth
constitutes a climatically determined or natural 'tree-line', referred to by
some as the natural 'timber-line'. The timber-line is referred to by foresters,
however, as the limit some way below the tree-line where trees no longer produce
2.2 The upper zone of woodland is called the sub-alpine zone. Classically this is the transition between the closed forest and the tree-less alpine zone. Here, tree growth is stunted by the severe climate, tree cover may be patchy, occurring in clumps or as scattered trees, and the trees are often accompanied by tall shrubs. There may be no clear boundary between these sub-alpine woods and the more continuous well-grown forests of the forest zone below, especially if the same tree species of the forest zone continue up into the subalpine zone.
2 3 In some parts of the world the tree species which grow in the sub-alpine zone are the same as those which occur in the forest zone, though in parts of Scandinavia Norway spruce (Picea abies) or Scots pine (Pinus sylvestris) forest gives way with an increase in altitude to birch (Betula pubescens ssp tortuosa) woodland. These natural altitudinal birch woods, typically mixed with juniper (Juniperus communis) and Salix spp., constitute the subalpine zone in Scandinavia Where there is continuity in species cover there is a gradation between the forest and sub-alpine zones, and any attempt to set boundaries is arbitrary. In this case the sub-alpine zone may be loosely defined as the zone in which tree growth becomes progressively stunted due to exposure and snow-lie. The growth-form of the trees may become that of 'krummholz' or stunted and twisted trees, where branches become spreading, or even prostrate in form. Damage occurs due to the weight of snow breaking branches, frost or exposure to wind. Both dominance by birch, forming a zone of sub-alpine woodland or scrub, and progressions of forest zone trees into the subalpine zone, especially perhaps Scots pine, probably once occurred widely in Scotland. Odd severely stunted individual trees may occur above the tree-line forming a 'cripple-limit'
2 4 Hester (1995), in a review of scrub in the Scottish uplands, defines scrub as 'all tree or shrub growth (excluding ericoid and prostrate dwarf shrubs) less than 5 metres in height'. This provides a useful, if arbitrary, height limit to distinguish sub-alpine 'scrub' from the forest below
2 5 A natural tree-line occurs in only a few places in the British uplands. Creag Fhiaclach in the Cairngorms is the most well-known and authentic. Here, at around 640m, creeping and contorted, and short but straight, and stunted Scots pine (Pinus sylvestris) grow together at an apparently climatically determined upper tree level, growing with jumper. There is a natural progression above to alpine juniper scrub and tall heather, and then to prostrate heather on severely wind-swept ground In some western areas, e.g. above Ballachulish in Glen Coe, patches of birch scrub may be reaching their natural altitudinal limit
2.6 Throughout the bulk of the British uplands natural tree-line woodland and scrub has been destroyed by grazing and burning. The upper limit of the woodland that remains is generally depressed well below its potential, natural limit. The true upper limit of tree growth is represented by scattered trees on crags and in other rocky places inaccessible to grazing animals. Woodland is generally fragmented and represented by scattered patches. Some birch woods in the Highlands, while rarely reaching their natural upper limit, may be equivalent to the sub-alpine birch woods of Scandinavia. However, in most areas in the uplands dwarf-shrub heath and grassland has replaced the natural woodland of the both the sub-alpine and forest zones. Some habitats are azonal e g blanket bog
2 7 Above the natural tree-line the alpine zone is dominated by low-growing shrubs of jumper or willow, and by ericoid dwarf-shrub heaths, dwarf-herb communities, moss-heath, grass-, sedge- and rush-heaths and snow-bed communities. In Scotland low-growing shrubs, such as willow (Salix spp) and juniper, are very local, and are usually confined to steep rocky localities difficult to burn or inaccessible to grazing animals.
2 8 On the European Continent (in particular in Scandinavia) the alpine zone is divided into low, middle and high alpine zones. Above these are the nival zones of rock, snow and scattered mosses, lichens and cushion plants where, on average, snow-fall exceeds snow-melt.
2 9 The low alpine sub-zone is the zone of dominance by jumper, willow, ericoid dwarf-shrub heaths, dwarf-herb communities, moss-heaths and grass-dominated snow-beds. The middle alpine sub-zone is the zone of dominance by sedges, rushes and snow-tolerant mosses. In Scandinavia the middle alpine sub-zone is defined floristically as that in which blaeberry (Vaccinium myrtillus) is squeezed out of the snow-beds because it cannot tolerate very prolonged snow-cover. This definition appears to work reasonably well in Britain where a small range of high-altitude communities, generally only developed above an altitude of about 900m, have a low frequency of V. myrtillus compared with communities immediately below them in altitudinal zonation. In the National Vegetation Classification (Rodwell 1992) the types of vegetation which define the middle alpine sub-zone in Britain are U8: Carex bigelowii-Polytrichum alpinum sedge-heath, U9a Juncus trifidus-Racomitrium lanuginosum rush-heath, Cladonia arbuscula-Cetraria islandica sub-community, U11 Polytrichum norvegicum-Kiaeria starkei snow-bed, and U12 Salix herbacea-Racomitrium heterostichum snow-bed Contrasting low-alpine types immediately below them, in which Vaccinium myrtillus is dominant or frequent, include U7 Nardus stricta-Carex bigelowii grass-heath, U10 Carex bigelowii-Racomitrium lanuginosum moss-heath and H19 Vaccinium myrtillus-Cladonia arbuscula heath.
2 10 The high alpine sub-zone on the Continent is the zone where low temperatures and unstable, raw soils, due to frost action and prolonged snow cover, maintain an open vegetation. According to Poore & McVean (1957) few mountains in Scotland have vegetation belonging to the high alpine. Exposure on the highest tops of the Ben Nevis range and the Cairngorms may limit the development of continuous vegetation in the same way as on the Continent, giving instead open fell-fields of rock debris with scattered plants. There are no NVC types, as currently described, from these fell-fields. We therefore doubt that there is any high alpine vegetation in Britain. The nival zone is absent from Britain
2 11 The widespread loss of natural tree-line scrub means that it is difficult to fix the altitudinal limits of vegetation zones in Scotland. At the only place in Scotland where there is a well-defined natural tree-line (Creag Fhiaclach on the Cairngorms) this attains an altitude of 640m. Pears (1967,1968) based on experiments that took exposure to wind into account suggests that on exposed slopes the potential tree-line is unlikely to exceed 610m while it would probably extend to 685m in sheltered localities. The transition between the forest and sub-alpine scrub is an arbitrary one and has been lost almost everywhere, except on Creag Fhiaclach from where no altitude data for the change are available. Spence (1960) gives altitudes for the probable lower and upper limits of the sub-alpine zone. The figures are based on the mean temperature of the warmest month and take exposure into account. The range of sub-alpine scrub is given as 640-840m for the central Highlands, 300-500m for Rum and 50-220m for Shetland, figures for west Sutherland are 100m lower than for Rum Existing fragments of scrub are found to lie within these limits.
2 12 The above figures are estimates for the lower altitudinal limit of the alpine zone in respectively exposed and sheltered localities According to Poore and McVean (1957) the middle-alpine zone begins at an altitude of 1200m on the Cairngorms and 1000m on
Beinn Eighe in the north-west Highlands, but locally may extend downwards if exposure or snow lie is excessive. According to Rodwell (1992) the lower limits of most of the characteristic communities of the middle-alpine zone he between 823 and 915m.
2 13 The arctic is the treeless tundra north of the polar tree-line, or limit of tree-growth in the far north. The sub-arctic constitutes a natural transition zone (the forest tundra ecotone) between the treeless arctic zone and the vast circumpolar zone of boreal forest (taiga)
(Hustich 1979). The sub-arctic forest tundra is characterised by mosaics of forest or krummholz or tree islands in sheltered places and arctic tundra on exposed ridges (Love 1970). The natural transitions between boreal forest, sub-arctic forest tundra and treeless arctic tundra parallels that between the forest, sub-alpine and alpine zones on mountains further south. The terms arctic and sub-arctic are occasionally used in referring to vegetation zones on British mountains, but such usage is inappropriate
2 14 Boreal is the northern biogeographical region, referring to the regions of northern Scandinavia and Russia with vegetation dominated by the taiga or evergreen coniferous forests. The dominant trees are Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), with needle-like leaves that can withstand prolonged freezing and snow cover, and dry periods. Downy birch (Betula pubescens) woods are well-developed in the sub-alpine zone, above the coniferous forests. A range of bogs, mires and dwarf-shrub heaths, some of them similar to those in Britain, also occur in the boreal regions. There is a range of plants characteristic of the boreal region, some of which also occur in Britain.
2 15 The term boreal is often applied to those kinds of vegetation occurring in Britain, especially in the Scottish Highlands, that are similar to those of the boreal zone. In Britain they form oceanic or Atlantic outliers of Continental boreal types. Notably these include Scots pine woods, Calluna-Arctostaphylos spp heaths, and high-altitude blanket bog.
2 16 Boreo-alpine is usually used as a biogeographical term, referring to plants and animals with disjunct distributions occurring both in Scandinavia and in the Alps or other mountain ranges in central or western Europe. Arctic-alpine is similarly used to refer to disjunct species distributions.
3 1 Ratcliffe and Thompson (1988) and Ratcliffe (1977) preferred to use the
terms sub-altitudinal vegetation zones on mountains in montane and
referring to Britain According to them the sub-montane zone includes all
vegetation derived from forest above the limits of enclosed farmland. The
montane zone includes everything lying above the potential tree-line Therefore,
the upper limit of the sub-montane zone equates with the upper limit of the
sub-alpine zone, and the montane zone is equivalent to the alpine zone of
Continental workers (Fig 2)
3 2 In normal Continental usage these terms are used to refer to the vegetation zones below the sub-alpine and alpine zones i e the upper forest zones (hence they differ from British usage as given in 3 1) In central Europe sub-montane woods are dominated typically by beech (Fagus sylvatica) with some oak.
3 3 (Quercus spp), hornbeam (Carpinus betulus) and Scots pine. Above them montane woods consist of beech mixed with various conifers including spruce (Picea spp), larch (Larix decidua), silver fir (Abies alba) and various species of pine (Pinus spp). Fir and spruce increase in dominance at higher levels.
3.4 Virtually all of sub-alpine woodland and scrub has been lost to grazing and burning in the British uplands. Thus, most of the sub-montane zone (sensu Ratcliffe and Thompson 1988) is occupied by open heaths, typically heather (Calluna vulgaris) moorland, and grasslands. Upland woods lying above the limit of enclosed farmland lie within the sub-montane zone and there is no reason not to refer to sub-montane forest or woodland. One example of this usage is Rodwell (1991a) who refers to Scots pine woodland as being characteristic of the cooler parts of the sub-montane zone in Britain.
Fig. 2. Diagram to illustrate British and Continental usage of terms applied to altitudinal zonations of vegetation in the uplands
3.5 Clearly, confusion can arise over the British and Continental usage of sub-montane
and montane. Our recommendations below (5) attempt to avoid this confusion.
4 1 Forest zone: zone of continuous well-grown forest not severely stunted by
4 2 Sub-alpine zone: zone of stunted, dwarfed or 'krummholz' trees, birch woodland and tall shrubs - up to the 'tree-line1 or climatic limit of tree growth, forming a scrub that may be arbitrarily defined as being of less than 5m tall (grading into the forest below). Also in Britain, within this and the forest zones, there are open habitats of heaths, bogs and grasslands which vary considerably in size and extent.
4 3 Alpine zones: vegetation zones which occur above the natural tree-line This divides into three sub-zones, namely
These are shown in Fig 1
We should endeavour to refer to upland habitats, embracing all land lying above the upper limit of enclosed farmland, using Continental terminology. We recommend use of the following terms for vegetation zones, in ascending altitudinal order
6 1 Terms such as arctic and sub-arctic, sub-montane and montane, and boreal
appear in the EC Habitats Directive (European Commission, 1992) and the CORINE
Manual (CORINE, 1991). Below we clarify usage of these terms in relation to
Scottish upland habitats Numbers refer to the Corine reference number given in
the CORINE Manual or in Annex I of the EC Habitats Directive.
6 2 Sub-Arctic
In Britain this habitat type chiefly corresponds to the NVC type W20 Salix
lapponum-Luzula sylvatica scrub, which is a rare type confined to the Highlands,
primarily in localities inaccessible to grazing animals. Stands of sub-Arctic
willow scrub in the Highlands belong mainly to the alpine vegetation zone,
though some patches of the constituent willows also occur within the sub-alpine
6 3 In the CORINE Manual the only locality given is the Highlands of Scotland. The latest Interpretation Manual of European Union Habitats (European Commission, 1995) also includes Finland and Sweden as having the habitat, since these countries recently joined the EU. As Britain lies well below the sub-arctic regions of northern Scandinavia (lying between the treeless arctic and boreal coniferous forests, 2 13) it may seem odd that this habitat is regarded as occurring here. The habitat is characterised by a group of willow species that occur mainly in northern Scandinavia and in other areas in the far north, representing an Arctic-Subarctic geographical distribution (Matthews 1955) Most of the willows occur as southern outliers in Britain, usually growing at high altitude where climatic conditions resemble the sub-arctic regions of northern Scandinavia.
6 4 Sub-montane and montane (Continental usage)
In normal Continental usage these terms are used to refer to the vegetation zones of moderate elevation below the sub-alpine and alpine zones i.e. the upper forest zones (3 2), hence they differ from British usage (3 1)
6 5 Sub-montane and montane are applied to sub-types of the CORINE Manual habitat type 31 Heath and scrub as follows.
6 6 Alpine and sub-alpine
31 4 Alpine and sub-alpine heaths (EC Habitats Directive Annex I)
Alpine and sub-alpine are used here as in normal Continental usage as defined
above (2 1-2.10)
6 7 Boreal and boreo-alpine
Sections 2 14 - 216 provide definitions of Boreal and boreo-alpine terms.
6 8 The sub-types of 31 4 Alpine and subalpine heaths occurring in Scotland are referred to as 31 45 Boreo-alpine Scottish heaths in the CORINE Manual. The three NVC equivalents of these heaths (H13. Calluna vulgaris-Cladonia arbuscula heath, H15. Calluna vulgaris-Juniperis communis nana heath and H17 Calluna vulgaris-Arctostaphyios alpina heath) are all heaths of the alpine zone of the Highlands and Islands. Floristically similar heaths to the Calluna-Arctostaphylos alpina heath occur in Scandinavia. In the CORINE Manual the term 'boreal' has been applied to Scotland rather than the northern parts of Scandinavia to which it is usually applied.
6.9 36 32 Siliceous alpine and boreal grasslands (EC Habitats Directive: Annex I)
Similarly with Siliceous alpine and boreal grasslands the NVC equivalents of these grasslands (U7 Nardus stricta-Carex bigelowii grass-heath, U8 Carex bigelowii-Polytrichum alpinum sedge-heath, U9 Juncus trifidus-Racomitrium lanuginosum rush-heath and U10 Carex bigelowii-Racomitrium lanuginosum moss-heath) are plant communities exclusively of the alpine zone in Britain. Equivalents of the these communities occur in Scandinavia, though in the CORINE Manual they are referred to as 'boreo-alpine formations of the higher summits of Scotland, Cumbria, northern England and northern Wales'. Revision of the CORINE Manual will be necessary now that Sweden and Finland have joined the EU.
610 Biogeographical regions of the EC Habitats Directive (European Commission 1992) "Alpine", "Boreal" and "Continental" are biogeographical regions legally established under the Directive (Hopkins and Buck, 1995) Great Britain lies within the "Atlantic" biogeographical region. Habitats may occur outside their characteristic biogeographical region.
6 11 We will produce another Information and Advisory Note with an interpretation of the full range of upland EC Habitats Directive and CORINE terms and habitats.
Baxter, C. and Thompson, D (1995) Scotland: Land of Mountains Colin Baxter
Brown, A , Horsfield, D & Thompson, DBA. (1993). A new biogeographical classification of the Scottish Uplands I Descriptions of the vegetation blocks and their spatial variation. Journal of Ecology, 81,207-230
Brown, A , Birks, H.J B & Thompson, D.B A (1993) A new biogeographical classification of the Scottish uplands II Vegetation -environment relationships Journal of Ecology, 81,231-251
CORINE (1991) Commission of the European Communities, CORINE Biotopes Manual Vol 1-3 CEC Director-General, Environment, Nuclear Safety and Civil Protection, Luxembourg.
Ellenberg, H (1988) Vegetation Ecology of Central Europe 4th ed. Cambridge University Press, Cambridge
European Commission (1992) Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora.
European Commission (1995). Interpretation Manual of European Union Habitats.
Directorate-General XI Environment, Nuclear Safety and Civil Protection, Luxembourg
Hester, A J (1995) Scrub in the Scottish Uplands Scottish Natural Heritage Review No 24 SNH, Battleby
Hopkins, J J & Buck, AL (1995) The Habitats Directive Atlantic Biogeographical Region. Report of Atlantic Biogeographical Region Workshop, Edinburgh, Scotland, 13-14th October 1994 JNCC Report No 247 Peterborough
Hustich, I (1979) Ecological concepts and biogeographical zonation in the North the need for a generally accepted terminology Holarctic Ecology, 2, 208-217
Love, D (1970) Subarctic and sub-alpine where and what? Arctic and Alpine Research, 2, 63-73
Matthews, J R (1955) Origin and Distribution of the British Flora Hutchinson, London
McVean, D N and Ratcliffe, D A (1962) Plant Communities of the Scottish Highlands. Monographs of the Nature Conservancy No 1 HMSO, London
Pears, N V (1967) Present tree-lines of the Cairngorm mountains, Scotland Journal of Ecology, 55, 815-830
Pears, N V (1968) The natural altitudinal limit of forest in the Scottish Grampians Oikos, 19, 71-80
Polunin O and Walters, M (1985) A Guide to the Vegetation of Britain and Europe. Oxford University Press, Oxford
Poore, MED and McVean, D N (1957) A new approach to Scottish mountain vegetation Journal of Ecology, 45, 401-439
Ratcliffe, DA (Ed) (1977) A Nature Conservation Review Volume 1 Cambridge University Press, Cambridge
Ratcliffe, D A and Thompson, D B.A (1988) The British uplands their ecological character and international significance In Ecological Change in the Uplands (M B Usher and DBA Thompson, eds), pp 9-36 Blackwell Scientific Publications, Oxford
Rodwell, J S (Ed) (1991a) British Plant Communities 1. Woodlands and Scrub Cambridge University Press, Cambridge
Rodwell, J S (Ed) (1991b) British Plant Communities. 2. Mire and Heaths Cambridge University Press, Cambridge
Rodwell, J S (Ed) (1992) British Plant Communities. 3 Grasslands and Montane Communities Cambridge University Press, Cambridge
Spence, D H N (1960) Studies on the vegetation of Shetland III Scrub in Shetland and South Uist, Outer Hebrides Journal of Ecology, 48, 73-95
Thompson, DBA and Brown, A (1992) Biodiversity in montane Britain habitat variation, vegetation diversity and some objectives for conservation Biodiversity and Conservation, 1, 179-208
Usher, M B and Balharry, D (1996) Biogeographical Zonation of Scotland Scottish Natural Heritage, Perth
Dave Horsfield and Des Thompson
Scottish Natural Heritage
2 Anderson Place
EDINBURGH EH6 5NP
Tel 0131-447 4784
We are grateful to the following for comments or advice Dr Helen Armstrong, Prof
H J B Birks, Allan Drewitt, Joanna Drewitt, Alan Hampson, Dr John Hopkins, Dr
Jayne Manley, Angus MacDonald, Dr Derek Ratcliffe, Prof Michael B Usher, Dr Will
Williams and Marcus Yeo
Back to menu