Mountain Heaths & Willow Scrub

This habitat occurs in the montane zone above the natural tree-line. It encompasses a diverse range of near-natural vegetation. These are found mostly above 600m in altitude, but in the north-west Highlands and Scottish Islands they occur to 300m or, in places, even lower. Some of the types are characteristic of exposed ridges and summits – others are restricted to sheltered situations where snow lies late. They are typically maintained by cool, windy conditions, low temperatures, extreme wind exposure, prolonged snow-cover, freeze-thaw and/or nutrient-poor, thin soils.

 

Montane heaths

These include a range of vegetation types (see below) that occur either above the altitudinal tree-line (i.e. Alpine heaths) or below it in gaps among scrubby high-altitude woods or in place of woodland lost due to grazing and burning (i.e. Boreal heaths).

 

Prostrate dwarf shrub montane heaths

  • The most common and visually distinctive montane heaths are the prostrate heather Calluna vulgaris communities. Here, heather grows in a purple-brown carpet with stems creeping sinuously over the ground away from the direction of the prevailing wind. Although there are species-poor forms, with little other than the heather itself, generally there is a mat of either  Racomitrium lanuginosum moss or lichens such as Cladonia arbuscula, Cladonia rangiferina, and Cetraria islandica.
  • There are similar prostrate bilberry/blaeberry Vaccinium myrtillus and mountain crowberry Empetrum nigrum ssp. hermaphroditum montane heaths, which also have lichen-rich and Racomitrium-rich forms. These are strikingly attractive, with rich green dwarf shrubs spangled with golden bryophytes or crisp, cream-white lichens.
  • Two other forms of prostrate montane heath are far less common. Calluna-Juniperus communis ssp. nana heath is a speciality of the north-west Highlands. Here, the mat of heather is interspersed with patches of dwarf juniper Juniperus communis ssp. nana with its conspicuous mats and clumps of waxy, grey-green, sharp-leaved stems. Calluna-Arctostaphylos heath has a much more mixed and variegated sward, where the prostrate heather intermingles with shrubs such as bearberry Arctostaphylos alpinus, dwarf juniper, mountain bearberry Arctostaphylos alpinus, mountain crowberry, and trailing azalea Loiselurea procumbens.
  • All of the above types are home to an array of small montane species such as stiff sedge Carex bigelowii, Alpine Clubmoss Diphasiastrum alpinum, dwarf willow Salix herbacea and bog bilberry Vaccinium uliginosum, as well as other diminutive upland plants such as Fir Clubmoss Huperzia selago, eyebright Euphrasia officinalis and tormentil Potentilla erecta.

 

Other montane heaths

  • The Vaccinium myrtillus-Rubus chamaemorus community is not a prostrate heath, but has a very short sward of heather or bilberry/blaeberry or both, growing with bog bilberry, cowberry Vaccinium vitis-idaea, mountain crowberry, stiff sedge and, in many examples, cloudberry Rubus chamaemorus and drawf cornel Cornus suecica. It is a damp heath with much Sphagnum capillifolium in the richly-coloured underlay of large mosses.
  • Some examples of the upland heath types Calluna vulgaris-Vaccinium myrtillus, Vaccinium myrtillus-Deschampsia flexuosa, and Scirpus cespitosus-Erica tetralix also occur in the montane zone and include montane species.

 

Summit heaths

The vegetation of high summits, ridges and plateaux consists of distinctive plants that can tolerate extreme environments.

 

Types of vegetation on summit heaths

  • The most widespread and extensive summit heath is Carex-Racomitrium heath. This is commonly known as ‘Racomitrium heath’ and it clothes large areas of high montane ground in a deep, soft, even, golden-green, carpet of Racomitrium lanuginosum moss. In a few places the dominant moss is Racomitrium ericoides. This heath varies from species-poor forms, with little other than Racomitrium moss and stiff sedge, to herb-rich forms, with species like Alpine bistort Persicaria vivipara, Alpine lady's mantle Alchemilla alpina, cyphel Minuartia sedoides, moss campion Silene acaulis, thrift Armeria maritima, and, in some localities, scarce species such as Alpine saw-wort Saussurea alpina, mountain chickweed Cerastium cerastioides, and the mosses Hypnum hamulosum and Aulacomnium turgidum. These herb-rich moss heaths are delightful in summer, when the warm air can be alive with insects, drawn to the nectar of small, bright flowering herbs set against the background moss carpet.
  • Some high altitude Juncus squarrosus-Festuca ovina grassland swards can be classed as montane heath, where they include montane species. These generally occur on thin peat, where they may be an anthropogenic replacement for montane blanket bog.
  • On the stony wildernesses of the highest summits, there are even more attenuated plant communities. These include thin swards of the three-leaved rush Juncus trifidus growing in small clumps or circular patches, together with dwarf willow, stiff sedge, Racomitrium lanuginosum and lichens. On some of the higher summits, lichen-dominated heaths occur. These consist of carpets of lichens, such as Alectoria nigricans, Cetraria islandica, Cladonia arbuscula and Coelocaulon aculeatum, growing in pale patches dotted with bilberry/blaeberry, stiff sedge and dwarf willow.
  • On high montane plateaux snow beds, where the snow is late-lying and the soils are damp, Carex-Polytrichum sedge heath occurs. This resembles grassland from a distance, but actually consists of dense swards of stiff sedge with its distinctive black flower heads.
  • Finally, fell-fields form an unusual type of vegetation that occurs on wind-exposed ridges and summits covered by fine gravel. At first glance they appear devoid of vegetation, but a few species are at home here, such as viviparous sheep's-fescue Festuca vivipara, Alpine lady's mantle, wild thymeThymus polytrichus, starry saxifrage Saxifraga stellaris, great wood-rush Luzula sylvatica, and mosses such as Oligotrichum hercynicum, Polytrichum piliferum and, on basalt, Racomitrium ellipticum.

 

Montane grasslands

The most extensive habitat in the high mountain zone is montane grassland. This near-natural vegetation occurs above the tree-line, where the snow lies too late or too deep for dwarf shrubs to survive. Such grassland characteristically forms large continuous tracts, across summit plateaux and the tops of higher summits and ridges. The flora is characterised by a strong montane element, including several uncommon vascular plants, mosses and liverworts. It is also the most important habitat for Eurasian dotterel Charadrius morinellus, Britain’s only montane wading bird. The vegetation is represented by a range of grassland types whose composition is influenced by contrasting extremes of exposure and snow-lie.

 

Types of montane grassland

  • Most widespread are the Nardus stricta-Carex bigelowii snow-bed grasslands and the Deschampsia cespitosa-Galium saxatile grasslands. The first is the most extensive and conspicuous, with the component matgrass and stiff sedge forming pale swards in spring as the melting snow exposes the remains of last year’s leaves.
  • In addition, in the high north-facing corries of the Cairngorms, patches of montane snow-bed grasslands are dominated by wavy hair-grass Deschampsia flexuosa, growing in a dense, dark-green sward.
  • There are also sub-communities of the largely sub-montane Festuca ovina-Agrostis capillaris-Galium saxatile grassland and Nardus stricta-Galium saxatile grasslands that can occur in the montane zone and include montane species, such as stiff sedge, dwarf willow and Alpine Clubmoss Diphasiastrum alpinum. These, however, are generally an anthropogenic replacement in which grasses have been increased by grazing, trampling and manuring.
  • Finally, late-lie snow-bed communities dominated by bryophytes and dwarf-herbs are included within this habitat.

 

Snow-bed vegetation

Snow-bed vegetation is characteristic of extreme places, where snow lies throughout the winter and into spring or even late summer. It normally includes an array of species that are common to all the snow beds, such as Alpine Clubmoss, dwarf cudweed Gnaphalium supinum, dwarf willow, stiff sedge, starry saxifrage, and heath bedstraw Galium saxatile, in addition to bryophytes such as Conostomum tetragonum, Polytrichum alpinum, and Racomitrium ericoides.

 

Types of late snow-bed vegetation

  • Moss-dominated snow-beds.   These are partially described by the Polytrichum sexangulare-Kiaeria starkei snow-bed community. They consist of a short, tufted, green turf of montane moss species, such as Polytrichum sexangulare, Kiaeria falcata, and Andreaea alpina, which are more-or-less confined to this habitat, and others, such as Dicranum fuscescens, Oligotrichum hercynicum and Racomitrium heterostichum, which are less exacting. Around the upper rims of corries, such snow-beds are classified by deep golden patches of the moss Rhytidiadelphus loreus. Many other snow-beds consist of distinctive emerald-green swards of Pohlia ludwigii.
  • Liverwort-dominated snow-beds.   These appear un-vegetated to the uninitiated, so tiny are the plants. The miniature liverworts form a thin crust over the ground surface, with up to eight different species in a square centimetre! Typical species include Anthelia juratzkana, Barbilophozia floerkei, Gymnomitrion concinnatum, Lophozia sudetica and Marsupella alpina.
  • The remaining snow-beds have a richer array of vascular plants growing with mixtures of mosses and liverworts. The scattering of flowers makes the community easy to pick out in summer. They are encompassed by the Alchemilla alpina-Sibbaldia procumbens dwarf-herb community and part of the Salix herbacea-Racomitrium heterostichum snow-bed sub-community. Typical species include Alpine bistort, Alpine lady's mantle, creeping sibbaldia Sibbaldia procumbens, moss campion, and spiked woodrush Luzula spicata.
  • It is also common to find expansive snow-bed vegetation, consisting of assemblages of typical snow-bed species together with the fern Cryptogramma crispa, the grasses Festuca vivipara, Nardus stricta, Deschampsia flexuosa and Deschampsia cespitosa, and plants such as three-leaved rush, hard fern Blechnum spicant and alpine marsh violet Viola palustris.

 

Montane willow scrub

This is a distinctive habitat that supports many rare plants and animals of northern latitudes and high mountains. It incorporates a mixture of sub-arctic and alpine willow species:

  • Downy willow Salix lapponum is the most widespread and abundant. Other, less frequent, species include mountain willow Salix arbuscula, whortle-leaved willow Salix myrsinites, and woolly willow Salix lanata.

These montane willows are very sensitive to browsing. The habitat is, therefore, limited to inaccessible ledges and slopes, with damp, skeletal soils. Most individual stands are fragmentary and cover barely more than a few square metres. At its best this is a magnificent community, with the willows forming a low, contorted, silvery canopy on wet ledges streaming with water.

The ground flora beneath the willows varies considerably depending on the soil base-status and irrigating water:

  • On more acidic sites, bilberry/blaeberry Vaccinium myrtillus and bog bilberry Vaccinium uliginosum, typically grow through a mat of mosses, dotted with species such as Alpine bistort, Alpine lady's mantle, great wood-rush and hard fern.
  • On more base-rich rocks, this can be an extravagantly herb-rich community, with a luxuriant array of ferns and tall flowering herbs such as globe-flower Trollius europaeus, meadowsweet Filipendula ulmaria, rose-root Sedum rosea, smooth lady's-mantle Alchemilla glabra, wild angelica Angelica sylvestris, water avens Geum rivale, and wood cranesbill Geranium sylvaticum. Together, these form the sort of colourful, exuberant display more usually associated with herbaceous borders than high mountain cliffs.
  • Saxifraga aizoides-Alchemilla glabra banks form a related community of steep, wet montane slopes. It can also be breathtakingly attractive, with dripping mats of yellow and purple saxifrage Saxifraga aizoides/S. oppositifolia, spangled with small plants such as Alpine bistort, Alpine meadow-rue Thalictrum alpinum, Alpine lady's mantle, lesser clubmoss Selaginella selaginoides and smooth lady's-mantle.

 

Important species

In addition to supporting a variety of rare types of vegetation, montane heaths and willow scrub are home to many rare and local arctic-alpine plants and invertebrates. These include:

  • Amara alpina and Phyllodecta polaris beetles;
  • Micaria alpina and Tricca alpigena spiders;
  • Netted mountain Macaria carbonaria and Scotch burnet Zygaena exulans ssp. Subochracea moths;
  • Norwegian mugwort Artemisia norvegica and Whortle-leaved willow Salix myrsinites;
  • Northern prongwort Herbertus borealis moss;
  • Sub-arctic willow scrub and willow snowbeds.

It also provides important nesting habitat for other important upland birds, including dotterel, ptarmigan, purple sandpiper and snow bunting. The golden eagle and peregrine use these montane habitats as part of their feeding range.