The native pinewoods are Scotland’s most important forest ecosystem, providing a critical habitat for a wide range of species.
The native pinewoods of Scotland form part of the boreal forest, the conifer-dominated forest that occurs all around the northern hemisphere. Although Scots pine is the most widely-distributed conifer in the world, with a range that extends from western Scotland to eastern Siberia, and from north of the Arctic Circle in Norway to the Mediterranean, the native pinewoods of Scotland are unique and distinctive from the Scots pine woodlands that occur elsewhere in Europe and northern Asia, because of the absence of any other conifer tree in them.
Distribution in Scotland
Native pinewoods currently occur at a total of 84 sites in the north and west of Scotland, and these are detailed in the Caledonian Pinewood Inventory produced in 1998 by Forestry Commission Scotland. The combined area of these sites is estimated at 18,000 hectares, but the bulk of that is contained in a relatively small number of locations, where the larger pinewood areas are found. Some of the better known and larger sites include Beinn Eighe; Glen Affric; Glen Strathfarrar; the Black Wood of Rannoch; and those in the Cairngorms National Park, such as Rothiemurchus, Glenmore, Abernethy, Glenfeshie, Mar Lodge and Glen Tanar. Many of the smaller sites contain fewer than 100 mature trees, and some are remote and difficult to access.
In the past, after the end of the last Ice Age, the pinewoods covered much of the Highlands of Scotland, from Perth northwards. At their maximum distribution, about 4,000 years ago, they may have extended to 1.5 million hectares, although trees would not have grown everywhere within that area. From that maximum, the pinewoods were reduced in their extent partly due to climatic changes, as cooler and wetter conditions led to a lowering of the treeline in the mountains and an expansion of peat bogs in some areas. Human activities over many centuries were a direct cause of much forest loss, and by the 18th century the size and distribution of the pinewood remnants were comparable to what they are today.
As their name suggests, the native pinewoods are characterised by the Scots pine, which is the largest and longest-lived tree in the woodlands. Reaching a height of over 35 metres, and living in some cases for over 500 years (some pines in Norway and Sweden are even older, at more than 700 years old), the Scots pine is a keystone species in the forest, creating the structural framework of the habitat, and upon which many other species depend.
Although Scots pine predominates in the pinewoods, other trees also occur in them, including silver birch (Betula pendula), downy birch (Betula pubescens), rowan (Sorbus aucuparia), alder (Alnus glutinosa), aspen (Populus tremula), goat willow (Salix caprea), grey willow (Salix cinerea), eared willow (Salix aurita), juniper (Juniperus communis), holly (Ilex aquifolium), hazel (Corylus avellana) and oak (Quercus petraea). The birches are the most numerous, often forming large stands of their own amongst the pines, while the other species usually occur as scattered individuals or small groups, with, for example, alders growing in a linear pattern along the edge of watercourses such as rivers and lochs.
In many of the pinewood areas, particularly those to the west of the Great Glen, where the valleys are oriented in a roughly east- west direction, the pinewoods are mainly situated on the north-facing slopes (ie on the south side of the glens). The south-facing slopes contained a greater component of broadleaved trees, characterised by oak and hazel, as well as wych elm (Ulmus glabra) and bird cherry (Prunus padus) at lower elevations. Most of those have been lost, due to human exploitation, but the clear difference in north and south-facing aspects can still be seen in the glens, from Loch Arkaig north to Strathfarrar. The increased exposure to the sun of the south-facing slopes means they are generally drier and have lost fewer nutrients to leaching and run-off, so that they can support the more demanding hardwood trees. By contrast, the pinewoods generally occur on more acid soils, which are relatively poor in nutrients.
The pinewoods vary in their characteristics across the Highlands, due to the rainfall gradient from the wetter conditions in the west to the much drier eastern areas. Those in the west have a greater diversity of bryophytes and lichens associated with them, while juniper, which is adapted to drier conditions, is generally more abundant in the east. Silver birch is more common in the eastern pinewoods, while further west downy birch becomes more predominant in higher rainfall areas.
Under the canopy of the trees, the pinewoods have a distinctive field layer characterised by heather (Calluna vulgaris), wavy hair-grass (Deschampsia flexuosa) and shade-loving, acid-tolerant plants such as blaeberry (Vaccinium myrtillus) and cowberry (Vaccinium vitis-idaea), as well as various mosses. Several pinewood sub-communities have been identified, where a number of other species are prominent, including bell heather (Erica cinerea), cross-leaved heath (Erica tetralix) and sphagnum mosses (Sphagnum capillifolium and Sphagnum quinquefarium).
The visual character of the pinewoods varies both from site to site, and within individual sites, depending in part on the growing conditions experienced by the pines when they were young. In some areas, where the pines germinated at a wide spacing, the mature trees are broad and spreading, often with multiple parallel major branches, resembling a broadleaved tree such as oak in their overall shape. In other sites, the pines are straight-trunked and taller, with few lateral branches, indicating that they grew up close together. In more marginal sites, where the ground conditions are wetter, the pines can be stunted and sometimes gnarled, forming a type of bog woodland.
The pinewoods occur at various elevations, ranging from near sea level in some of the western woods such as Shieldaig and the Loch Maree Islands to almost 650 metres at Creag Fiaclach in the Cairngorms National Park. The latter site provides possibly the best example of a treeline woodland in Scotland today, with the pines being stunted and wind-shaped, and accompanied by juniper and montane willows (Salix spp.).
The inability of Scots pine to regenerate under its own canopy means that the pinewood areas are, in effect, mobile over extended periods of time. Young trees will germinate and grow in clearings or at the edge of the existing pinewoods, so that over a period of several centuries, as the old trees mature and die, the areas covered by pines will move around and change within a landscape.
The native pinewoods are ecological communities comprised not just of trees, but of a wide range of organisms, from fungi and invertebrates to flowering plants, birds and mammals, all of which interact with, and are dependent on, other parts of the ecosystem. The pines themselves provide a living habitat for many species, such as the lichens that grow on their trunks and the birds that nest in their canopies.
Fundamental to the stability and resilience of the pinewood ecosystem is the mycorrhizal relationship between the trees and fungi. This mutualistic or symbiotic partnership benefits the trees, which receive nutrients that the fungi access in the soil, passed to them by the fungal hyphae thread-like filaments that sheath the trees’ roots. It also benefits the fungi, as they receive sugars and carbohydrates that the trees produce through photosynthesis, fungi cannot access the sun’s energy directly themselves. Of particular note in the pinewoods are the rare tooth fungi that grow in mycorrhizal association with the pines. They are distinguished by having teeth instead of gills on the underside of their caps, and are listed as priorities for conservation under the UK BAP. A large number of other commoner fungi also form mycorrhizal relationships with Scots pine, and the individual species involved change over time as the trees grow to maturity. Some fungi, such as the chanterelle (Cantharellus cibarius), are mycorrhizal partners for birches as well as pine.
The native pinewoods are noted for a number of special plant species, some of which are quite rare. These include twinflower (Linnea borealis), which is common in boreal forests elsewhere in Europe and North America but scarce and very localised in Scotland, most likely due to its relative inability to recolonise sites from where it has been lost. Creeping ladies tresses (Goodyera repens) is a perennial orchid that spreads by above-ground runners as well as by seed. Several different wintergreens are found in the pinewoods, of which one-flowered wintergreen (Moneses uniflora) is the most significant, because of its comparative rarity.
A large variety of insects and other invertebrates live in the pinewoods, many of them occupying special ecological niches such as dead wood or in the bark crevices of trees. Amongst the most obvious are the wood ants, which make distinctive nests on the forest floor. The Scottish wood ant (Formica aquilonia) and the hairy wood ant (Formica lugubris) are widely distributed, while the slavemaker ant (Formica sanguinea), which enslaves the young of other ant species, is much scarcer. The narrow-headed wood ant (Formica exsecta) is highly localised, only occurring in some of the pinewoods in the Strathspey area. Wood ants are important predators in the pinewoods, controlling the numbers of herbivorous insects, and thereby providing some protection to the trees from defoliation. They also have a symbiotic relationship with aphids, which they ‘milk’ for the honeydew that is an aphid waste product and in return they guard the aphids from predators and parasites.
Wood ants themselves are prey for other species, and the wood ant spider (Dipoena torva) specialises in catching them, hunting on the trunks of pines where the ants ascend to feed from aphids in the canopy. Other notable insects in the pinewoods include two rare hoverflies (Callicera rufa and Blera fallax), which breed in wet rot-holes in standing pine trees and pine stumps respectively.
Invertebrates are food for many of the insectivorous birds that live in the native pinewoods, such as the crested tit (Lophophanes cristatus). This is one of the forest’s characteristic species, and it nests in hollows in standing dead Scots pines. Other important birds in the pinewoods include the Scottish crossbill (Loxia scotica), which is the only bird endemic to Scotland, and the capercaillie (Tetrao urogallus), which is the largest member of the grouse family. It was hunted to extinction in Scotland in 1875 but then successfully reintroduced from Scandinavia in 1837. However, capercaillie numbers have decreased dramatically in the past 20 years, and it is at risk of dying out in Scotland for a second time.
The native pinewoods support a good diversity of mammals, ranging from wood mice (Apodemus sylvaticus) and voles to the badger (Meles meles) and fox (Vulpes vulpes). They are particularly important as the stronghold for the red squirrel (Sciurus vulgaris), which has been displaced from many parts of the UK by the non-native grey squirrel (Sciurus carolinensis). Other key species in the pinewoods include the pine marten (Martes martes) and the Scottish wildcat (Felis silvestris silvestris), which is now very rare and endangered in Scotland. The largest surviving mammal is the red deer (Cervus elaphus), which has adapted to live in the treeless glens, but is by nature a forest-dwelling species for most of the year. Extirpated species that are missing from the pinewoods include wild boar (Sus scrofa), Eurasian lynx (Lynx lynx) and the wolf (Canis lupus).
Despite their official protected status, many of the pinewood areas are not in good ecological condition, and often consist almost entirely of old trees, of 200 years or more in age, with no recruitment of young pines having occurred for two centuries. This is due to an imbalance between excessive numbers of large herbivores, particularly red deer and domestic sheep (Ovis aries), and too few trees, with the consequence that all the naturally germinating seedlings are eaten as soon as they grow above the level of the ground vegetation such as heather. In the final decades of the 20th century, measures to address this problem, either with deer fencing or through greatly increased culls of the deer, were instigated at a number of the main sites, including Beinn Eighe, Glen Affric, Abernethy and Glenmore, amongst others, and a new cohort of younger pines have become established in them. This still leaves a legacy of a missing generation of trees between 40 years and 200 years old, and this will result, in due course, in an absence of veteran or ancient pines in virtually all the pinewoods for many decades, until the younger trees reach maturity. The native pinewoods of the Caledonian Forest are listed as a priority for conservation in the European Union’s Habitats Directive of 1992, which, together with the Birds Directive, forms the cornerstone of the Union’s nature conservation policy. As a result the UK has an international obligation to protect and restore the pinewoods, and this is reflected in their inclusion as a priority habitat in the UK Biodiversity Action Plan (BAP).
Many of the larger pinewood areas are protected as National Nature Reserves (NNRs), including Abernethy, Beinn Eighe, the Loch Maree Islands, Glen Affric, Glen Tanar, Glenmore, and Invereshie and Inshriach. Other pinewoods are protected as Sites of Special Scientific Interest (SSSI), including the Black Wood of Rannoch, Glen Strathfarrar, Coulin, Rhidorroch, Amat, Loch Arkaig and the Liatrie Wood in Glen Cannich. Some of the pinewoods are also protected within Special Areas of Conservation (SAC), a European level designation under the European Union’s Natura 2000 network that was developed as an output from the Habitats Directive.