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
utilizable timber.
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
montane when
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
climate
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
zone.
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
Publications, Grantown-on-Spey
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