Borrowdale Atlantic Rainforest

Britain's Forgotten Rainforest

Borrowdale is known for its rain. It is the wettest inhabited valley in England, a deep glacial trough running south from Derwentwater into the heart of the Lake District, where clouds pile against the surrounding fells and release their moisture in quantities that seem, at times, almost tropical. The hamlet of Seathwaite, at the valley's head, records an average annual rainfall of 3,552 millimetres -- roughly three times the national average. It rains here on more than two hundred days a year. The air is saturated. The stone walls drip. The becks are always full.

And in this relentless wetness, something extraordinary survives: fragments of temperate rainforest.

The term surprises people. Rainforest is supposed to be equatorial -- steaming jungles of mahogany and liana, toucans and tree frogs. But rainforest is defined by rainfall, not by temperature, and there is a second kind: temperate rainforest, found not in the tropics but in the cool, maritime margins of the world's continents. Where warm ocean currents meet western coastlines, where rainfall is high and persistent, where humidity rarely drops and frost rarely bites, a particular kind of forest can develop -- one dominated not by the towering canopy trees of the tropics but by ancient, twisted oaks and birches, their branches so thickly coated in mosses, liverworts, lichens, and ferns that the trees themselves seem almost secondary. The epiphytes are the spectacle. The trees are merely the scaffolding.

This is the Atlantic rainforest, sometimes called the Celtic rainforest. Globally, temperate rainforest is rarer than its tropical counterpart. It exists in narrow coastal strips: the Pacific Northwest of North America, southern Chile, Tasmania, New Zealand, parts of Japan, western Norway -- and the western fringe of Britain and Ireland. In these islands, it clings to the mild, wet coastlines of western Scotland, Wales, Devon, Cornwall, and parts of Cumbria and Ireland, wherever the conditions are right: high rainfall, mild winters, clean air, and enough time for the extraordinary communities of lower plants to establish themselves.

Borrowdale is one of the finest examples in England.

The Borrowdale Woods

The rainforest fragments of Borrowdale are not a single continuous wood but a series of separate oakwoods scattered along the valley sides, clinging to the steep, rocky slopes where agriculture never reached and sheep have only intermittently grazed. The most important are Johnny's Wood, on the eastern side of the valley above Rosthwaite; Seatoller Wood, further south near the hamlet of Seatoller; and the woods around Castle Crag, the small but dramatic rocky peak that guards the jaws of Borrowdale where the valley narrows between the flanks of High Spy and King's How.

These are ancient woodlands. They are not plantations or recent growth but remnants of the wildwood that covered this valley after the last glaciation -- sessile oakwoods that have been here, in one form or another, for thousands of years. The sessile oak (Quercus petraea) is the dominant tree, its trunk shorter and more twisted than the pedunculate oak of the lowlands, its branches spreading horizontally from gnarled boles that seem to grow from the rock itself. Among the oaks grow birch, rowan, holly, hazel, and the occasional ash or alder. The understorey is dense in places -- hazel and holly forming a secondary canopy beneath the oaks -- and open in others, where the ground is too rocky or too steep for anything but moss-covered boulders and the exposed roots of the oaks themselves.

The woods have a particular character that distinguishes them from ordinary English oakwoods. The trees are not tall. The canopy is relatively low, shaped by the wind that funnels through the valley and by the thin, acidic soils of the volcanic rock. The trunks and branches are twisted and contorted, bending around boulders and reaching for whatever light the valley provides. And every surface -- every branch, every trunk, every rock, every fallen log -- is covered in a thick, continuous coat of green.

This is the rainforest element: the epiphytes.

The Epiphytes: A Living Coat

The diversity of mosses, liverworts, and lichens in the Borrowdale woods is astonishing. These are among the richest bryophyte communities in Europe -- assemblages of lower plants that thrive in the valley's particular combination of high rainfall, high humidity, mild temperatures, clean air, and ancient, undisturbed substrate.

Bryophytes are the mosses and liverworts -- small, non-vascular plants that lack the roots, stems, and water-conducting tissues of higher plants. They absorb water directly through their tissues, which means they are utterly dependent on atmospheric moisture. In dry environments they desiccate and go dormant. In the saturated air of Borrowdale, they flourish.

The tree trunks are upholstered in deep cushions of moss -- species such as Isothecium myosuroides, Hypnum cupressiforme, and Thamnobryum alopecurum -- that in places form a coat several centimetres thick. Liverworts grow among the mosses, their flattened, lobed thalli pressed against the bark in intricate overlapping layers. The rarer species are here too: leafy liverworts of the genera Plagiochila, Frullania, and Metzgeria, some of them nationally scarce, found in only a handful of sites in Britain.

Lichens add another dimension. These composite organisms -- part fungus, part alga or cyanobacterium -- encrust the branches and hang from the twigs in pale, filamentous curtains. The tree lungwort (Lobaria pulmonaria), a large, lettuce-like lichen that was once common across Britain's western woodlands, survives here. It is an indicator species for old-growth forest and clean air; its presence confirms the ecological continuity of these woods.

Polypody ferns complete the picture. Common polypody (Polypodium vulgare) grows along the upper surfaces of branches, its fronds arching outward from the mossy bark, giving the trees the appearance of carrying their own aerial gardens. In places, a single oak branch will support mosses, liverworts, lichens, and ferns simultaneously -- a miniature ecosystem sustained entirely by the moisture in the air.

The overall effect is of a forest from another age. The green is overwhelming -- not the green of leaves but the green of moss, a softer, deeper, more saturated colour that covers everything in sight. On a wet day (which in Borrowdale is most days), the woods feel primeval, hushed, and ancient. Drops of water hang from every surface. The air smells of damp earth and decaying wood. The only sounds are the dripping of water and the calls of woodland birds -- pied flycatchers, wood warblers, redstarts -- that breed in the oak canopy in spring.

The Rain

Borrowdale's rainforest exists because of Borrowdale's rain, and Borrowdale's rain exists because of geography. The valley faces west-northwest, directly into the path of the prevailing Atlantic weather systems. Moist air, warmed by the Gulf Stream, travels across the Irish Sea and strikes the high fells of the central Lake District -- Great Gable, Scafell Pike, Great End -- which rise to over 900 metres at the head of Borrowdale. The air is forced upward, cools, and releases its moisture as rain. Seathwaite, at 128 metres above sea level, sits at the base of this orographic funnel, receiving the full benefit of the forced precipitation.

The result is extraordinary. Seathwaite's average annual rainfall of 3,552 mm makes it the wettest continuously inhabited place in England. On 19 November 2009, the Seathwaite rain gauge recorded 316.4 mm in 24 hours -- the highest daily total ever recorded in England at the time. The Borrowdale Fells as a whole receive well over 4,000 mm on the higher ground. Styhead Tarn, above Seathwaite, is estimated to receive over 5,000 mm annually.

This rain is not seasonal. Unlike tropical rainforests, which may have distinct wet and dry seasons, Borrowdale receives rain throughout the year. The wettest months are October to January, but there is no dry season. The humidity remains high even in summer, and the cloud cover is persistent. These conditions -- constant moisture, no drought stress, rarely any hard frost -- are precisely what temperate rainforest species require.

Ecology of the Canopy and Floor

The sessile oak dominates the canopy, but the ecology of these woods is more complex than a simple monoculture. The canopy structure is irregular, with gaps created by fallen trees, rocky outcrops, and variations in soil depth. These gaps admit light to the forest floor, creating a mosaic of habitats.

Birch (Betula pubescens and B. pendula) colonises gaps and open ground, its lighter canopy admitting more light than the oaks. Rowan (Sorbus aucuparia) is common on the rockier slopes, its berries providing autumn food for thrushes and fieldfares. Holly (Ilex aquifolium) forms a dense, evergreen understorey in places, its glossy leaves catching the dim winter light. Hazel (Corylus avellana) grows as an understorey shrub, coppiced in places in past centuries for charcoal, poles, and hurdles.

The ground flora is dominated by bilberry, hard fern, and various grasses on the drier slopes, with wood sorrel, golden saxifrage, and opposite-leaved chrysosplenium in the wetter hollows. The soil is thin, acidic, and heavily leached by the constant rain, limiting the ground flora compared to richer lowland woodlands. But the diversity is carried by the epiphytes, not the ground plants. In a temperate rainforest, the real biodiversity is on the trees, not beneath them.

Dead wood is critically important. Fallen trunks and standing dead trees support their own communities of mosses, liverworts, fungi, and invertebrates. The wood-decay fungi -- bracket fungi, coral fungi, earth tongues -- are an important component of the woodland's ecology, recycling nutrients back into the thin soils.

Threats

These rainforest fragments are survivors, but they are not secure. Several threats press upon them.

Overgrazing by sheep has been the most persistent and damaging pressure. Sheep eat tree seedlings, preventing natural regeneration. Where sheep have had free access to the woods for generations, the result is an aging canopy with no young trees coming through to replace it -- a woodland slowly dying of old age. The understorey is suppressed, the ground flora impoverished, and the mosses and liverworts on lower trunks and rocks are damaged by trampling.

Invasive rhododendron (Rhododendron ponticum) is a serious threat. This vigorous, shade-tolerant shrub, introduced from the Mediterranean in the 18th century as an ornamental, has colonised many western British woodlands, forming dense, impenetrable thickets that shade out native plants and smother the bryophyte communities on rocks and lower trunks. Removal is difficult and ongoing.

Climate change poses longer-term risks. Although increased rainfall might seem beneficial, changes in seasonality, increased summer drought events, and rising temperatures could disrupt the delicate balance of moisture and temperature that sustains the bryophyte communities. Species adapted to cool, constantly moist conditions may be unable to tolerate even short periods of drought.

Air pollution, particularly nitrogen deposition from agricultural ammonia and vehicle emissions, affects lichens disproportionately. Many lichen species are exquisitely sensitive to changes in air chemistry. While Borrowdale's air quality is generally good by national standards, background nitrogen deposition remains a concern for the most sensitive species.

Conservation

The Borrowdale woods are designated as a Site of Special Scientific Interest (SSSI) in recognition of their exceptional bryophyte communities and ancient woodland character. Many of the key woodland areas are owned and managed by the National Trust, which has undertaken significant conservation work in recent decades.

The most important intervention has been grazing reduction. The National Trust has fenced sections of woodland to exclude sheep, allowing natural regeneration to occur. The results have been dramatic: within fenced areas, young oaks, birch, and rowan have appeared in numbers not seen for generations. The understorey is recovering. Mosses and liverworts are recolonising lower trunks and rocks from which they had been trampled away.

Rhododendron clearance is ongoing, a laborious process of cutting, stump-treating, and follow-up management to prevent regrowth. Volunteers and conservation teams work through the woods each winter, gradually pushing back the rhododendron and restoring light and space to the native plant communities.

These woods are also part of a broader national effort to recognise and protect Britain's temperate rainforest. Conservation organisations, including Plantlife, the Woodland Trust, and the Alliance for Scotland's Rainforest, have drawn attention to the rarity and fragility of this habitat, arguing that it deserves the same level of recognition and protection as tropical rainforest. The Celtic rainforest, they point out, is a globally rare biome, and Britain and Ireland hold a significant proportion of the world's remaining examples.

The Broader Celtic Rainforest

Borrowdale is part of a much larger story. The Atlantic or Celtic rainforest once covered much of Britain and Ireland's western seaboard -- a continuous belt of oceanic woodland stretching from Cornwall to Cape Wrath. Today, only fragments remain.

Scotland's west coast holds the largest surviving areas, particularly in Argyll, Lochaber, Sunart, and Wester Ross. Glen Creran, Ariundle, and the Sunart oakwoods are among the finest examples, their birch and oak canopies supporting bryophyte communities of international importance.

Wales retains significant fragments in Snowdonia, the Cambrian Mountains, and Pembrokeshire, where the Ty Canol and Pengelli woods harbour rich lichen and moss floras.

Devon and Cornwall hold small but important remnants, particularly in the river valleys of Dartmoor (the Teign, the Dart, Wistman's Wood) and on the north Cornish coast.

Ireland's Atlantic coast, particularly in Kerry and west Cork, supports rainforest fragments that are among the most species-rich in Europe for bryophytes and lichens.

All of these sites share the same essential conditions: high rainfall, mild winters, clean air, and long ecological continuity. And all face similar threats. The Celtic rainforest is a biome under pressure, fragmented and diminished but not yet lost. Borrowdale's woods are a reminder of what once existed across the whole of western Britain -- and of what, with careful management, might yet be restored.

Visiting the Borrowdale Rainforest

The Borrowdale woods are freely accessible to walkers. There is no admission charge, and the paths through the woods are well-established, though often rough, steep, and wet.

Johnny's Wood is reached by a short walk from Rosthwaite, heading south along the valley path. A permissive path enters the wood and climbs through the oaks, with views across Borrowdale to Castle Crag.

Seatoller Wood lies south of the hamlet of Seatoller, at the foot of Honister Pass. Paths lead into the wood from the road.

Castle Crag can be reached from either Rosthwaite or Grange. The path from Grange follows the River Derwent through the jaws of Borrowdale, passing through woodland on both sides of the valley before climbing steeply to the summit. The woods on the lower slopes of Castle Crag are among the most atmospheric in Borrowdale.

The best time to visit for the epiphytes is autumn and winter, when the mosses and liverworts are at their most vibrant and the leafless oaks reveal the full extent of their green coat. Spring brings nesting birds and bluebells. Summer, though the driest season (relatively speaking -- this is Borrowdale), is warm and green.

Sturdy, waterproof footwear is essential at any time of year. The paths are rocky, rooted, and frequently muddy. Rain gear is advisable -- or, more accurately, inevitable. This is a rainforest, after all.

The National Trust manages the Borrowdale valley and provides car parking at Rosthwaite, Seatoller, and Grange. Bus services run along the valley from Keswick. Detailed walking routes are available from the National Trust and the Lake District National Park Authority.