Mountain Woodland

Defining mountain woodland is surprisingly tricky - a cause of debate in Scotland and beyond. In Scotland, mountain woodland is sometimes defined as all trees and shrubs growing above 400 m asl; however, in northern and western areas climatic conditions mean that traditional montane species and growth forms occur at lower altitudes. Perhaps the best approach is to recognise mountain woodland as the broad ecotone above the timberline (the maximum altitude at which upright single-stemmed trees occur).

What is mountain woodland?

Where is mountain woodland?

Currently, most high-altitude trees and shrubs are restricted to crags and steep-sided burns where they can escape the pressures of grazing. Some species, such as Salix arbuscula, survive grazing by taking on low creeping forms.

Although studying the past distribution of mountain woodland habitats is difficult, the majority view amongst conservationists is that mountain woodland habitats in Scotland have been restricted to inaccessible refugia by centuries of burning and grazing. It is our view that many species of trees and shrubs have the potential to be much more widespread across the Highlands than is currently represented by the existing fragments.

Montane willows

There are six native montane willow species in Scotland:

• Woolly willow - Salix lanata [Pictured right] -->

• Downy willow - Salix lapponum

• Whortle-leaved willow - Salix myrsinites

• Mountain willow - Salix arbuscula

• Net-leaved willow - Salix reticulata

• Dwarf willow - Salix herbacea

There are also two more submontane species:

• Dark-leaved willow (Salix myrsinifolia)

• Tea-leaved willow (Salix phylicifolia)

Other willow species do also occur at high- altitude:

• Goat willow (Salix caprea)

• Grey willow (Salix cinerea)

• Eared willow (Salix aurita)

• Creeping willow (Salix repens)

6

2

Native submontane willow species present at high-altitudes

Native specialist montane wilow species

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Other willow species which occur at high-altitudes

Betula

Betula pubescens subsp. czeraponazii,
Western Norway

Dwarf birch - Betula nana

Dwarf birch is a small dwarf shrub with a fragmented distribution across Scotland, mostly in areas of blanket bog. However in Scandinavia, dwarf birch is widespread and it may be more suited to growth on mineral soils.

Scottish Mountain Birch - Betula pubescens var. pumila (?)

The existence of a separate variety or subspecies of downy birch at high-altitudes in Scotland is a subject of considerable debate. The most recent paper on the topic (Amphlett, 2022) concludes that most high-altitude birch in Scotland is Betula pubescens var, fragrans, which also occurs at low-altitude. However, there are many old records of Betula pubescens var. pumila/ subsp. tortuosa/ subsp. czeraponazii from across Scotland. This subspecies - true "mountain birch" - is the result of clinal hybridisation with B. nana and is widespread in Norway (photographed near Ulvik, Western Norway).

Rock Whitebeam

Sorbus rupicola, Loch Maree

Rock Whitebeam - Sorbus rupicola
See BSBI Handbook No.14 (Rich et al., 2010)

Rock whitebeam is a shrub or small tree, with characteristics oval leaves. Apart from on the Isle of Arran, it is Scotland's only native whitebeam. The common whitebeam (S. aria) native to Southern England is widely planted, but S. rupicola has narrower leaves of which the lowest part are untoothed.

Rock whitebeam is endemic to Northwest Europe, and is the second most widespread Sorbus species in Britain (only rowan is more widely distributed). This is because, unlike the Arran whitebeam and the many other rare local endemic Sorbus microspecies, rock whitebeam is an old species, whose evolution predates the last ice age.

Rock whitebeam is apomictic, meaning it can set seed without fertilisation. A useful trait for isolated populations!

However, all is not as well as it seems with Scotland's rock whitebeam populations. Many populations are in fact single isolated trees, confined to refugia by intense grazing pressures. The effects of this long-term lack of gene flow due to this level of isolation is unclear.

As a hardy light-demanding species, with significant biodiversity benefits, there is great (so far largely unexplored) potential for rock whitebeam in mountain woodland restoration projects. We recently collected seed from the Loch Maree islands for NatureScot and Forestry and Land Scotland.

Juniper

Juniperus communis subsp. communis, Rothiemurchus Estate

Juniper (Juniperus communis) grows everywhere - well, nearly. We have recorded it from coastal dunes to waterlogged islands, pine forest to upland plateau. It is not, however, tolerant of high levels of grazing, burning and is currently threatened by Phytophthora austrocedra. As a component of mountain woodland, juniper has been lost from many treelines.

To survive in such a range of habitats, juniper takes on a multitude of forms. There are three recognised subspecies of juniper present in the UK, two of which are widespread in Scotland. Both subspecies occur at high-altitude and should not be distinguished by growth form alone.

Dwarf juniper (subsp. nana), is a small, prostrate plant identified by their smaller needles (<15mm - Stace, 1997) which taper abruptly into a point.

Common juniper (subsp. communis) exhibits a number of growth forms from a small tree to a dwarf shrub. The larger needles (<20mm - Stace, 1997) end in a long drawn out (acuminate) point.

Juniper "berries" (really cones) have a long period of dormancy and can be collected year-round.

Designations & Classifications

Montane willow scrub is protected as the Annex 1 Habitat 4080 Sub-arctic Salix scrub (in the UK this habitat falls within the subcommunity Pal. 31.622 - Boreo-Alpine willow brush). This habitat is a qualifying feature for Special Areas of Consevation such as Beinn Heasgarnaich SAC. For a population to qualify as potential Annex 1 H4080 habitat, the population of montane willows at the site must exceed 20 individuals with clusters no more than 100m apart (Sullivan, 2015).

Sub-arctic Salix scrub is a subset of the UK BAP & Scottish Biodiversity List Priority Habitat: Mountain Heaths and Willow Scrub.

Vegetation Communities
The only community of mountain willow scrub described in the NVC is W20 Salix lapponum-Luzula sylvatica scrub. However, there is significant variation in montane willow scrub habitats not recognised in the NVC due to their rarity. For example, stands of Salix myrsinites on limestone do not conform to existing NVC communities.

H4080

W20

Salix lapponum - Luzula sylvatica scrub

The Annex 1 habitat composed of montane willow scrub

Salix lapponum, Glen Lochay Estate
This population is sufficiently large and contiguous to qualify as H4080

Get in touch to discuss the potential for mountain woodland restoration in your area.