Habitat account - Temperate heath and scrub


4080 Sub-Arctic Salix spp. scrub 

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 4080 Sub-Arctic Salix spp. scrub.  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 4080 Sub-Arctic Salix spp. scrub. Click image for enlarged map.

Description and ecological characteristics

 

Sub-Arctic Salix spp. scrub is the UKs highest-altitude shrubby vegetation, occurring on moist, relatively base-rich soils in rocky situations on mountains. It is predominantly a natural habitat, with succession prevented by the harsh climate at the high altitudes at which it is found. It tends to be associated with the more sheltered areas of the upper subalpine and low alpine zones of mountains, and there may be a positive association with moderately late snow-lie. Stands of Salix scrub survive on ungrazed ledges and, more rarely, on lightly grazed, steep rocky slopes or boulder fields, occurring only as small, discrete stands or more scattered bushes. Grazing is believed to have reduced and restricted its occurrence. At many sites its continued future is precarious, since it is confined to often unstable rock ledges and reproducing populations are very small, isolated, and of uncertain long-term viability. The largest continuous stand of this very local habitat type is about 0.5 ha in extent and most stands are very much smaller.

 

The Annex I habitat type consists of a mixture of willow species which have arctic-alpine and arctic-subarctic distributions in Europe. Sub-Arctic species include downy willow Salix lapponum, whortle-leaved willow S. myrsinites, mountain willow S. arbuscula and woolly willow S. lanata. Associated arctic-alpine and northern willows include net-leaved willow S. reticulata, dark-leaved willow S. myrsinifolia and tea-leaved willow S. phylicifolia. The willows grow among a rich mixture of dwarf shrubs, grasses, rushes and broad-leaved herbs, such as bilberry Vaccinium myrtillus, tufted hair-grass Deschampsia cespitosa, great wood-rush Luzula sylvatica and Alpine ladys-mantle Alchemilla alpina, and the habitat supports many rare plants and animals of northern latitudes and high mountains. On the rock ledges Sub-Arctic Salix spp. scrub commonly mixes and associates with stands of 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels.

 

Several willow species may be found on the same site, but the most abundant willow varies from patch to patch of the habitat both within and between sites. Some of this variation may be related to the base-richness of the underlying substrate, the altitude of the stands or, more locally, the effects of grazing. The habitat usually occurs on soils developed on schist, which vary from strongly to weakly calcareous, and also on limestone. Different species of willow demand greater or lesser amounts of lime in the rocks. S. lapponum is relatively undemanding and can grow on lime-poor schist. It is therefore the most widespread species because lime-poor rocks are widely distributed. S. lanata, S. myrsinifolia and S. reticulata are more lime-demanding and are rare because suitable lime-rich rocks are localised. S. arbuscula is more resistant to grazing than other willow species and is found very locally on slopes open to grazing. S. lanata, the rarest willow species, forms patches where there is marked base-rich flushing. S. reticulata is a very low growing shrub which rarely forms scrub and is found more frequently in 6170 Alpine and subalpine calcareous grasslands. S. myrsinifolia and S. phylicifolia occur only at the lower end of the altitudinal range of the habitat.

 

In the UK this vegetation corresponds partly to NVC type W20 Salix lapponum Luzula sylvatica scrub, but other types of willow scrub also fall within the definition of the Annex I type. S. lapponum is not necessarily the most frequent or abundant willow species in all stands of Salix Luzula scrub, and other species such as S. lanata and S. myrsinites may be abundant. S. myrsinites scrub on limestone (a community which is not described in the NVC) is also included in this habitat. Stands of dominant S. lapponum, S. myrsinites, S. lanata and S. arbuscula are all included in the habitat.

 

The constituent willows of Sub-Arctic Salix spp. scrub also occur occasionally in a range of other habitats, including several Annex I types. On slopes open to light grazing, Sub-Arctic Salix spp. scrub gives way to 6170 Alpine and subalpine calcareous grasslands, 6230 Species-rich Nardus grasslands, on siliceous substrates in mountain areas (and submountain areas in continental Europe) and 4060 Alpine and Boreal heaths.

European status and distribution

 

Sub-Arctic Salix spp. scrub is a rare habitat, restricted in the Atlantic Biogeographical Region to mountains in the UK, Sweden and Finland. In Scandinavia Sub-Arctic Salix spp. scrub merges with tree-line birch woodland at high altitudes and high latitudes. Similar types of willow scrub occur more rarely in the mountain ranges of central and southern Europe, but these lack the Arctic willow species such as Salix lanata.

UK status and distribution Click to view UK distribution of this habitat

 

Sub-Arctic Salix spp. scrub is one of the UKs most rare and endangered habitats, and is almost confined to the higher mountains of the Scottish Highlands where it is a relict of post-glacial vegetation. Fragmentary stands of the habitat occur in the Southern Uplands of Scotland and in Cumbria.

Site selection rationale

 

The SAC series reflects the UKs special responsibilities for conserving montane willow scrub. The sites selected hold a high proportion of the largest known patches of scrub and include stands with the best-developed community structure and regeneration. They contain the largest known populations of the constituent willow species, in particular the sub-arctic species Salix lapponum, S. myrsinites, S. arbuscula and S. lanata. Site selection has also taken account of ecological and floristic variation over the geographical and altitudinal range of the habitat, and encompasses different rock types on which the habitat type occurs.

 

The SAC series covers the main geographical range of the habitat in the Breadalbane Hills, eastern and central Highlands, together with outliers in the north-west Highlands. Most sites have representation of W20 Salix Luzula scrub, while Inchnadamph, Ben Alder and Ben Lawers (which has fragmentary Salix Luzula scrub) support willow scrub types not fully described in the NVC. Fragmentary stands south of the Highlands were considered too small and lacking adequate habitat structure and function to be included as qualifying SAC features.


Site accounts

Ben Alder and Aonach Beag Highlands and Islands
This site in the central Highlands is selected to represent high-altitude (950m) Sub-Arctic Salix spp. scrub on highly calcareous schist and limestone. It has the largest known population in the UK of woolly willow Salix lanata, the rarest of the sub-Arctic willows. Downy willow S. lapponum and net-leaved willow S. reticulata are frequent, and whortle-leaved willow S. myrsinites is also represented. The willows are associated with an area of 6170 Alpine and subalpine calcareous grasslands on steep, rocky and remote ground.
Ben Heasgarnich Eastern Scotland, Highlands and Islands
Ben Heasgarnich is one of four sites selected in the Breadalbane Hills of the southern Highlands and represents Sub-Arctic Salix spp. scrub up to high altitude (950m) on highly to moderately calcareous schist. W20Salix lapponum Luzula sylvatica scrub is widely-developed on the site, although it is virtually confined to crags and rock ledges, where the individual colonies of willows are small. The most abundant willow species are downy willow Salix lapponum, mountain willow S. arbuscula, whortle-leaved willow S. myrsinites and net-leaved willow S. reticulata. The scrub is associated with a rich flora of tall herbs and with stands of 6170 Alpine and subalpine calcareous grasslands.
Ben Lawers Eastern Scotland
Ben Lawers is one of four sites selected in the Breadalbane Hills of the southern Highlands and represents Sub-Arctic Salix spp. scrub with mountain willow Salix arbuscula. The site has the largest known population of S. arbuscula in the UK, developed on steep, rocky slopes and crags that are difficult for grazing animals to reach. It also occurs on some open grazed areas where it is highly prostrate. Ben Lawers also supports fragmentary stands of W20Salix lapponum Luzula sylvatica scrub on calcareous schist at moderately high altitudes. Other willows are restricted to crags and rock ledges. Species include downy willow S. lapponum, dark-leaved willow S. myrsinifolia and net-leaved willow S. reticulata, together with scattered plants of woolly willow S. lanata. Generally the Salix scrub is associated with 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels or 6170 Alpine and subalpine calcareous grasslands.
Ben Lui Eastern Scotland, Highlands and Islands
Ben Lui supports W20Salix lapponum Luzula sylvatica scrub, occurring on highly calcareous schist at moderate altitude. The scrub is well-developed on an extensive series of schistose crags and rock ledges. Unlike at most other sites, the dominant species is whortle-leaved willow Salix myrsinites. This variant also occurs at Inchnadamph (where by contrast the scrub occurs at low altitude on limestone). Net-leaved willow S. reticulata is frequent, mainly associated with areas of calcareous grassland. Mountain willow S. arbuscula, tea-leaved willow S. phylicifolia and downy willow S. lapponum are also represented. The scrub has a rich flora and is associated with 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels and 6170 Alpine and subalpine calcareous grasslands.
Caenlochan Eastern Scotland, North Eastern Scotland
Sub-Arctic Salix spp. scrub is relatively frequent at Caenlochan, growing to a high altitude on highly to moderately calcareous schist. Corrie Sharroch holds the largest single patch (around 0.5ha) of W20Salix lapponum Luzula sylvatica scrub remaining in the UK. The scrub is also found spread across a larger area of crag and steep rocky slope than on any other site in the UK. The most abundant species, and generally the dominant one, is downy willow Salix lapponum, which probably occurs in larger numbers here than on any other site in the UK. There is a relatively large patch of scrub dominated by woolly willow S. lanata, and the site may hold the second-largest population of this species in the UK. Whortle-leaved willow S. myrsinites and net-leaved willow S. reticulata are also present. The associated habitat is mainly 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels.
Creag Meagaidh Highlands and Islands
Creag Meagaidh is representative of W20 Salix lapponum Luzula sylvatica Sub-Arctic Salix spp. scrub on less calcareous schist in the west-central Highlands at moderately high altitude (600750 m). The site includes examples of scrub in an exceptionally wide range of different situations and associated vegetation types. Clumps of willows are widely scattered in corries on crags and rock ledges, along rocky or steep burn-sides, in boulder fields, in Carex Juncus flushes, and in flushed ground in association with mountain saxifrage Saxifraga aizoides. Downy willow Salix lapponum is the most common species, while mountain willow S. arbuscula and dark-leaved willow S. myrsinifolia are also represented.
Drumochter Hills Eastern Scotland, Highlands and Islands
Drumochter Hills is representative of W20Salix lapponum Luzula sylvatica Sub-Arctic Salix spp. scrub on less calcareous schist in the east-central Highlands at moderately high altitude (750m). Patches of scrub are widespread across the site and are thought to constitute the second-largest area of scattered scrub in the UK after Caenlochan. The habitat occurs in a variety of locations, including rock ledges, crags, by rocky burn-sides and, unusually, in wet scree on steep slopes. Exceptionally, in one place the scrub occurs with subalpine scrub of rowan Sorbus aucuparia and downy birch Betula pubescens. The most frequent and widespread willow species is downy willow Salix lapponum, while whortle-leaved willow S. myrsinites and mountain willow S. arbuscula occur locally.
Inchnadamph Highlands and Islands
Inchnadamph is the most northerly site selected for Sub-Arctic Salix spp. scrub and has a unique development of whortle-leaved willow Salix myrsinites scrub on limestone at low altitude. This is the largest area of this form of Salix scrub in the UK. The scrub occurs in and around outcrops of Durness limestone, and Inchnadamph and Rassal are the only siteswhere this habitat type is solely developed on limestone. There are significant transitions to 8240 Limestone pavements, for which the site is also selected.
Meall na Samhna Eastern Scotland
Meall na Samhna is one of four sites selected in the Breadalbane Hills of the southern Highlands for Sub-Arctic Salix spp. scrub and represents W20Salix lapponum Luzula sylvatica scrub on highly calcareous schist at moderately high altitude (around 750m). The wide range of species present is characteristic of calcareous schistose rock, and includes woolly willow Salix lanata, downy willow S. lapponum, whortle-leaved willow S. myrsinites, mountain willow S. arbuscula and net-leaved willow S. reticulata, which are mixed together. The willows are confined to rock ledges and occur in two main patches across a series of crags. They are mainly associated with 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels and 6170 Alpine and subalpine calcareous grasslands, with exceptionally rich suites of associated arctic-alpines.
Strathglass Complex Highlands and Islands
Strathglass is the best representative in the SAC series of W20Salix lapponum Luzula sylvatica scrub on generally base-poor schist up to high altitude in the north-west Highlands. The Sub-Arctic Salix spp. scrub occurs in a series of localities in two widely separated corries, and scattered plants also occur in a few other places. The main occurrences are on ungrazed rock ledges, on steep rocky ground (including boulder fields) and on open slopes, where the willows are heavily grazed. Associated habitats are 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels and herb-rich grassland. While downy willow Salix lapponum is the most widespread willow species, whortle-leaved willow S. myrsinites is also present.

SACs/SCIs/cSACs where this Annex I habitat is a qualifying feature, but not a primary reason for site selection

Beinn Dearg Highlands and Islands
Ben Nevis Highlands and Islands
Cairngorms Highlands and Islands, North Eastern Scotland
Glen Coe Highlands and Islands
Rassal Highlands and Islands
 

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