Woodland Flowers

Great Britain and Ireland were connected to each other and the main mass of Europe for thousands of years, allowing free movement of species whenever conditions were suitable. Rising sea levels separated Great Britain and Ireland about 11,000 years ago. Then, about 7,000–8,000 years ago, the final land bridges between Great Britain and the Continent were lost. Doggerland disappeared under the North Sea and the chalk between Dover and Calais was cut through to form the English Channel. However, our woods still remain outposts of those that spread across the Continent, our flora and fauna a subset of that for Europe as a whole. The differences in our woodland flora arise from the peculiarities of our climate and soils, and in the history of land use in Great Britain and Ireland compared to that on the Continent.

A wood in the Pas de Calais, France, but it could be in the Weald of Sussex.

Virtually all our woodland plants can be found somewhere else in Europe. Some species, such as the Oxlip and Italian Lords-and-Ladies, are almost accidental parts of our flora, occurring in only a few places and at the limits of their range. Other species, such as Bluebell, Welsh Poppy, Primrose and Stinking Iris, are more widespread in Great Britain than generally across the Continent and should command more attention in conservation debates. I remember the glee on the local foresters’ faces in Poland and again in Estonia, when they promised to take us to see a ‘rare plant’ that turned out to be Ivy! In Great Britain it is of course common, but it gets scarcer and more confined to ground-creeping, the further east you go. The plant we saw in Poland only grew about 30cm up a tree and then it stopped – any further and it risked being above the snow cover in winter and the buds would have been killed by frost.

Europe can be divided into a series of broad regions that reflect the major differences in its vegetation. The distribution of individual plant species does not correspond precisely to these areas, but the degree to which a plant’s range overlaps different regions may provide clues as to what is limiting their occurrence (Dahl 1998). For example, Wild Madder shows a southerly and westerly distribution (southern Atlantic and Mediterranean regions), Oak Fern Gymnocarpium dryopteris more of northerly (Boreal) and Central European distribution, and Mistletoe an Atlantic and Central European distribution.

Stinking Iris, more common in Great Britain than on the Continent.

Great Britain lies in the Atlantic Zone, which is characterised by low temperature variations between summer and winter. Rainfall occurs in every season, which means that there is usually ample soil moisture for active plant growth through spring and summer. Atlantic species may be limited by winter temperatures further east and north. The distributions of Black Bryony, Bluebell and Gorse, for example, correspond very roughly to a mean temperature for the coldest winter month of +2°C or warmer. Species such as Scaly Male-fern and Great Wood-rush spread further east and north, corresponding roughly to the -4°C line. Hardier plants such as Wild Garlic and Hard-fern can be found within the zone defined by the -8°C line, thus spreading well into the Boreal Zone.

Some species with their centre of distribution in the Boreal and Central European zones occur in Great Britain, for example Beech Fern, Wood Crane’s-bill, Chickweed-wintergreen, Common Cow-wheat and Mountain Melick. Their seed may depend on a period of more intense winter cold before it will germinate; or they may be vulnerable in mild winters, because they rely on snow cover to protect the plant or seeds from extremes of cold and frost, as with the Ivy in Poland.

Coming in from central and southern Europe, and more dependent on high summer warmth, are Southern Wood-rush, Narrow-leaved Helleborine, and the less-demanding Meadowsweet, Toothwort, False Brome and Wood-sedge. Least well represented in our woodland flora are plants from the Mediterranean zone; for example, the Wild Gladiolus now occurs only in the New Forest.

Wood-sedge, a species with central and southern European affinities.

Most of the woodland communities found in Great Britain are linked to those on the Continent (Rodwell & Dring 2001). Our beechwoods are the western end of a vast complex of mixed beechwoods found across Europe, with for example a beechwood over Box in the Cevennes looking not unlike one on the North Downs. Heinz Ellenberg listed the plants in samples taken from a beechwood on fertile soils in the Jura Mountains on the French–Swiss border (Ellenberg 1988). There were of course no bluebells, but the main species – Dog’s Mercury, Bugle and Wood Anemone – are common in British woods. Eleven others, including Ivy, Early Dog-violet, Yellow Archangel and Herb-Paris, would not look out of place in a Chilterns beechwood. Five species in his list occur in Great Britain but are generally rare – Spiked Rampion, Martagon Lily Lilium martagon, Lesser Hairy-brome Bromopsis benekenii, Fingered Sedge Carex digitata and Wood Fescue. This last occurs mainly on ledges in gorges in western Great Britain, but in the Wye Valley it spreads out over the forest floor, mirroring its behaviour in Ellenberg’s Jura sample. Four species from his samples are not native to Great Britain, but two of these, Asarabacca Asarum europaeum and Spring Pea Lathyrus vernus, sometimes escape into woods from gardens. Our acid beechwoods show similar overlaps with the flora of Continental woods: we lack the White Wood-rush Luzula luzuloides as a native species (although it has naturalised in some places, on acid soils, often by streams) but we have a greater abundance of more Atlantic species such as Hard-fern, Butcher’s-broom and Slender St John’s-wort.

Beech over Box in the Cevennes, but it could be the North Downs.

Asarabacca is native on the Continent, but not in Great Britain – here growing in the Botanic Garden in Oxford.

Another of Ellenberg’s lists, from Oak–Hornbeam woods in the Hartz Mountains in Germany, includes Wood Anemone, Yellow Archangel, Wood Meadow-grass, Greater Stitchwort and Dog-violet as the common species. Of the 50 species named, 40 are native to Great Britain and not uncommon in our lowland mixed woods. A further four are British rarities (Martagon Lily, Spiked Rampion, May Lily and Unspotted Lungwort). The Continental additions are then Ground Elder and Lesser Periwinkle Vinca minor, both commonly naturalised in our woods; some less common garden escapes – Liverleaf, Asarabacca and Spring Pea; leaving just a bedstraw that does not occur in Great Britain at all.

The oakwoods of western Great Britain beyond the native range of Hornbeam are distinctive and of international importance because of the richness of their mosses and liverworts, which are favoured by our mild, moist climate. These conditions also encourage an abundance of ferns such as Hard-fern, the Shield-ferns (Polystichum aculeatum, P. setiferum), Male-fern and Broad Buckler-fern, with in places the more frost-sensitive Hay-scented Fern and Filmy ferns (Hymenophyllum wilsonii, H. tunbrigense), none of which are so common on the Continent. However, other species making up the ground flora of our oakwoods (Wavy Hair-grass, Bilberry, Heath Bedstraw and Heather) are the same as those found in acid oakwoods in the foothills of central Europe and around the Baltic.

Young Hornbeam among Oak in Poland, but it could be Hertfordshire.

Ashwoods are more prominent in Great Britain, because in central and southern Europe similar fertile woodland soils are usually dominated by Beech, Sycamore, Norway Maple or limes. Nonetheless where ashwoods do occur on the Continent they have many ground flora species that we would recognise. A grove of Narrow-leaved Ash (a close relative of our Ash) from the northern coastal region of Spain, for instance, boasted Wood Spurge, Bugle, Primrose, Betony Betonica officinalis, False Brome, Remote Sedge, Thin-spiked Wood-sedge and Lady Fern (Polunin & Walters 1985).

Oak coppice in the Czech Republic, but it could be Norfolk.

Other similarities between our ashwoods and the woods of Scandinavian river valleys are indicated by northern montane species such as Stone Bramble, Globeflower, Melancholy Thistle and Wood Geranium. This rich flora is also closely related to that found in traditional northern meadows (Peterken 2013). In northern Europe the wood-meadow was a distinctive part of local culture. Fine examples still survive in Estonia where ‘grassland’ and ‘woodland’ plants form colourful mixtures: Herb-Paris and Lily-of-the-valley hobnob with Cowslip Primula veris and Viper’s-grass Scorzonera humilis. Wood-meadows do not seem to have been widespread in Great Britain. Perhaps, because woodland was less extensive, it was easier to keep the hay meadows and the coppice woods separate.

Estonian ash wood-meadows with a right old mixture of species.

Polunin & Walters (1985) list 21 species from herb-rich birchwood flora from Iceland including Alpine Bistort Polygonum viviparum, Alpine Meadow Rue Thalictrum alpinum, Stone Bramble, Water Avens, Wood Crane’s-bill, Heather and Bilberry. All occur in Great Britain and there are similarities to the assemblages found in the ungrazed birchwoods of base-rich soils in Great Britain, such as Morrone Birkwood near Braemar.

Stone Bramble – a plant found in Icelandic birchwoods, but also at sites such as Morrone Birkwoods near Braemar.

The ground flora of Scandinavian Pine and Spruce woods described by Polunin & Walters (1985) with Wood-sorrel, Bilberry, Northern Buckler-fern Dryopteris expansa, Chickweed-wintergreen, Hairy Wood-rush and Wavy Hair-grass could be from a native pinewood in Scotland. To find May Lily in a Scottish pinewood would be a surprise, but Scots Pine on the Continent occurs across a wider range of conditions as native woodland than in Great Britain. However, in some cases we may have recent planted equivalents. The natural pinewoods on long-established dunes on the Continent find an echo in the older plantations on dunes at Ainsdale, near Liverpool, or Culbin Sands in north-east Scotland. The stunted pines on some Northumberland bogs derived from 17th/18th-century plantations are similar to the pines found naturally on mire systems on the Continent. Some mature spruce stands can have a similar appearance to semi-natural spruce stands in Sweden.

Yew is more abundant in Great Britain than on the Continent, where it now occurs primarily in the understorey of beechwoods. There are few deep groves of pure Yew such as occur on the chalk and limestone in Great Britain. Holly, a southern Atlantic species, also does particularly well with us. However, the understorey of these two heavy shading evergreens is distinctive only in being very poor.

The greater clearance and fragmentation of British woodland cover in the past compared to much of the Continent means that there are few large-scale landscapes where woodland types grade into one another in combination with other habitats. This does happen, though, on a small scale at Roudsea Wood in Cumbria, where the flora of acid and basic, free-draining and waterlogged woodland soils can be seen side by side, along with transitions to lowland raised bog and tidal estuary.

Our biggest rivers are quite small on a European scale. Any surviving strips of alder and willow alongside them are usually hemmed in by arable fields or intensive pastures. The water courses tend to be fixed, preventing the joyous meandering of the main channel that would once have taken down mature trees and exposed new ground to potential tree and herb colonisation. This process can be seen in the few large examples of braided channels that survive, as along the River Spey, or on a smaller scale at Urquhart Bay on the shores of Loch Ness. We have only fragmentary areas of wooded backwaters and swampy scrub, but perhaps more will develop in future in the areas where beavers have been reintroduced. On the Continent, wet woodland also often grades into tall, highly productive, mixed forests of Ash, Elm and poplars. This exists in fragmentary form in the New Forest, but more usually our native Black Poplar and Aspen (as a riverside tree) occur as scattered individuals, such that they are hardly thought of as woodland trees at all.

There are few places in Great Britain where you can see the altitudinal gradients in forest types that are common on the Continent, but at Talladale on Loch Maree a walk can take you from Oak by the lochside up through Birch to Pine at the upper levels. There is a change in the ground flora too, related to changing soil conditions, from Creeping Soft-grass and Bracken under the Oak with Tormentil, Bluebells and Wood-sorrel, to a flora with more Heather, Bilberry and Purple Moor-grass higher up. At Craig Fhiaclach in the Cairngorms there is a clear change in structure of the pinewood with increasing altitude, ranging from tall, little-branched trees, to the low twisted pines found at high altitude, but these are not accompanied by any major change in the ground flora.

Ireland has only about 70% of the vascular plant species considered native to Great Britain (Webb 1952, Preston et al. 2002), and this applies to its woodland flora as well. A surprise to me was the scarcity of Dog’s Mercury, although it is considered possibly native (Parnell et al. 2012). Other scarce or missing species include Herb-Paris, the two Bryony species, Spurge-laurel and Wood Spurge. There may be a temperature factor involved, as these plants have a southerly distribution generally in Europe, reach their north-westerly climatic limits in south-eastern Great Britain, and are largely absent from the West Country, Wales and western Scotland. Some of the species meeting their south-westerly limits in Great Britain, such as Melancholy Thistle, Wood Crane’s-bill and Globeflower (this last occurs in Ireland but in only a few places), might also be excluded by climatic factors. The absence of pinewood specialists such as Chickweed-wintergreen, Twinflower and Creeping Lady’s-tresses is not surprising, as until recently there were thought to be no native pinewoods surviving in Ireland (Roche et al. 2018).

Spurge-laurel, widespread in southern England, but absent as a native plant from Ireland.

Some species may simply not have spread back fast enough from southern Europe to reach Ireland before the split with Great Britain. They do not appear to be climate-limited because they grow well where they have been introduced. Wild Hop, an occasional relic of cultivation, is long-established in some locations; Old Man’s Beard is common, widely naturalised and may be spreading; Wall Lettuce is definitely introduced and now fairly common on limestone pavement, walls and in woodland.

On the plus side, the higher rainfall, and particularly its even spread through the year, increases the richness of the mosses and liverworts in Irish oakwoods. Hard, Hay-scented, Soft Shield and Hart’s-tongue ferns are more common in Ireland than in Great Britain, as is the eponymous Irish Spurge, which in Great Britain is limited to a few locations in Devon and Cornwall. Other ground flora plants that in Great Britain are more often found in woods, grow freely in open country in Ireland, for example Dog-violet, Primrose and Wild Strawberry.

Irish Spurge Euphorbia hyberna, a rare plant in Great Britain.

It is possible to visit Continental woods and find a ground flora that is quite different from anything that occurs in British woods. Polunin and Walters provide an example of Austrian Black Pine forest vegetation made up of Buckler Mustard Biscutella laevigata, Shrubby Milkwort Polygaloides chamaebuxus, Garland Flower Daphne cneorum, Spring Heath Erica carnea, Matted Globularia Globularia cordifolia and Blue Moor-grass Sesleria caerulea; only the last of which is native to Great Britain. However, as long as you do not go too far, the differences are more in the quantity of familiar species, or the replacement of a well-known one by a sister species, Oxlip for Primrose for example, with just a handful or two of totally new species to learn.

Our woods are part of the wide sweep of variation across Europe. These similarities and differences between our woods and those on the Continent have been important in developing conservation priorities (Rodwell & Dring 2001), particularly under the European Habitats and Species Directive. Our beechwoods and pinewoods are significant as some of the most westerly examples of their type, even though we only hold a small proportion of the total European extent. Our ravine and rocky slope ashwoods are floristically rich: they generally lack some of the tree species, such as Large-leaved Lime, that are widespread on the Continent, but they have more of the Atlantic fern species. Great Britain and Ireland have most of Europe’s moss and liverwort-rich oakwoods; we have in our wood-pastures an amazing survival of ancient trees, particularly oaks (Farjon 2017); and in the spring displays of bluebells are a world-class plant spectacle.

Looking across the Channel should give us hope that as the climate shifts more towards that currently experienced in southern and eastern Europe, many of our species may still be able to find a space in the changed woodland communities that develop. We might though reconsider our attitude to species found in European woods that are not native here, but sometimes escape from gardens into the wild. These might be the next stage in the continued development of our post-glacial flora. Often such escapes first appear along hedges or tracks through woodland, illustrating the role that these features play in linking woods into the surrounding landscape at a local scale.