Woodland Flowers

Ordnance Survey maps may encourage us to think of British landscapes as Green (wooded) and White (non-wooded) land, but many trees and shrubs occur outside woods, in hedges around rock outcrops, in field corners, along roadsides and by streams. Small streams provide a part-shaded, moist microclimate where woodland plants may survive in landscapes largely cleared of woodland, as George Peterken noted in his Lincolnshire study. Streamsides in the uplands may have more fertile soils than the adjacent open hill, allowing greater species richness, and can act as a refuge from grazing animals. Rock outcrops can similarly provide some shelter and more favourable conditions for woodland plants. An extreme example of this is the woodland plants in the deep cracks in the rocks on limestone pavement, such as Hart’s-tongue Fern, Green Spleenwort Asplenium viride and Herb-Robert, and rarer species such as the Dark-Red Helleborine Epipactis atrorubens.

The most obvious of these non-woodland habitats for woodland plants are hedges, estimated to stretch to about half a million kilometres (over 300,000 miles) in Great Britain. Open tracks and paths through woods (often called rides) fulfil an analogous, but reverse, function, allowing shade-intolerant plants to move into and survive within an otherwise largely closed habitat. Rides and hedges form complementary sets of lines through the landscape.

In poorly-wooded counties such as Cambridgeshire the extent of non-woodland trees may be several times that of the woods. Even in well-wooded Hampshire the non-woodland tree cover is the equivalent of half the wooded area (Brown & Fisher 2009). A hedge may be all that remains of a wood that has been cleared: these are sometimes known as ‘ghost hedges’. Some hedges mark field boundaries that may go back to the Iron Age, whereas others were only planted in the last few decades as part of agrienvironment schemes (Pollard et al. 1974, Watt & Buckley 1994). Their composition reflects differences in soil types and climate, but also the history of local landscapes (Rackham 1986). Parts of the country are characterised by small, irregularly shaped fields, with very mixed hedges; in other areas large, more regular, field patterns were formed from the parcelling-up of the farmland under parliamentary enclosure acts in the last couple of centuries.

The wildlife potential of hedges has long been recognised, and the oldest hedges tend to be the richest. The number of trees and shrub species in a 27.5m length very roughly corresponds to the age of the hedge in centuries, although the calculation could be out by 200 years either side! The rule is also invalidated where several species were deliberately planted to establish a mixed hedge. On the Isle of Man, the number of Bramble species present has been linked to hedge age, though the problems of identifying the different Bramble micro-species mean that this approach to aging hedges has not been widely used.

The association of woodland plants with hedges is reflected in the local names collected by Grigson (1975), for example Hedge Garlic and Hedge Poppy (Foxglove). Greater Bindweed is also known as Hedge Bells and Hedge Lily (Somerset), and Old-Man’s Beard as Hedge Feathers (Yorkshire). White Bryony might be called Hedge Grape (Worcestershire), but, as the berries are poisonous, do not use it to make wine. There are Hedge Lovers (Herb-Robert), Hedge Violet (Common Dog-violet, Devon), Hedge Maids (Ground-ivy, East Anglia) and Hedge Pink (Soapwort Saponaria officinalis, Hants). The Dog-rose might be Hedge-speaks in Gloucestershire but Hedgy-pedgies over the border in Wiltshire.

Woodland plants that occur in hedges are often tall-growing species that can tolerate high levels of light and moderately rich nutrient soils, such as Nettle, Hogweed, Cow Parsley, Ivy, Bramble and Cleavers. They need to compete alongside the coarse grasses often found in field margins such as Yorkshire-fog, Cock’s-foot and False Oat Grass. Smaller woodland specialist plants may though occur: even in dry Norfolk, Barren Strawberry, Bluebell and Wood Anemone can be found (Barnes & Williamson 2006), while in wet Wales, Primrose and Hart’s-tongue Fern are common along hedge-banks. The presence of a ditch may allow opportunities for some wet woodland plants such as Meadowsweet and Bittersweet.

If hedges start to thin out at the base through neglect, over-cutting or clearance of the trees and shrubs, the specialist woodland plants may decline but they are not always lost completely. The remnants of Dog’s Mercury, Bluebell or Lords-and-Ladies along a bank may indicate where a hedge used to be. A spreading hedge can equally be a threat, however, since few plants survive beneath the shade of very dense Blackthorn or Hawthorn.

Plants within the hedge may be afforded some protection from grazing by domestic stock, depending on the width of the hedge and whether it has been supplemented by a wire fence. However, rabbits and Muntjac also use hedgerows as the sites for burrows, or as convenient cover for their tracks, making plants in the hedge more vulnerable to being eaten.

Grassy strips along the edges of woods provide some buffering against the drift of herbicides applied to adjacent fields or overspill of fertilisers, as well as adding another element of habitat diversity. Fertiliser and pesticide placement have become more precise in recent years, but there may still be indirect effects where these re-volatilise and are then scavenged by the trees and shrubs in the hedge (chapter 16).

Hedges that are the remnants of old woods may have a rich woodland flora because the plants have just stayed where they were when the rest of the wood was cleared. With new hedges, generally the species have colonised after the hedge was created. Ernie Pollard and Max Hooper, then of the Nature Conservancy, showed in the 1970s that both legacy effects and colonisation could be important. The medieval section of a hedge that had once formed the boundary of Monks Wood in Cambridgeshire contained Dog’s Mercury, Wood Anemone and Bluebell, whereas these species were far less common in a newer, though still 150-year-old, adjacent hedge section. Resurveys of the same hedge in 1998, led by Tim Sparks, one of their successors at the Monks Wood Experimental Station, found all three species had declined in the old sections. By 2011 there had been some recovery in Dog’s Mercury and Bluebell (Mountford et al. 2012) and Wood Anemone was seen again in 2016. These three species seem to be behaving as survivors from an earlier woodland phase. However, other woodland plants such as False Brome, Black Bryony, Groundivy and Germander Speedwell had spread into the new section.

In another hedge study in Northamptonshire from the early 1970s Dog’s Mercury was considered to have spread along two old enclosure hedges attached to an ancient wood at about a metre a year (Pollard et al. 1974). Dog’s Mercury was still there in 2017 and appeared to have spread a bit further away from the wood in the intervening 40 years. However, the hedges had expanded out from the original line, creating a dense Blackthorn thicket, five or six metres wide, with little beneath the bushes. The surviving Mercury patches were not very vigorous, just scattered clumps. There was a clear animal path down the centre of the hedge, so seeds may be being carried along on the coat of a Muntjac. This was probably also the source of a small Bluebell clump established some way from the wood-edge. In another two hedges the Dog’s Mercury was more vigorous and still had a more or less continuous presence along the hedgerow. These were narrow hedges, regularly trimmed, and mainly Hawthorn rather than Blackthorn.

Hedges can therefore be important habitats for woodland plants, particularly woodland generalists, provided they are managed sympathetically. In addition, colonisation of new woods by plants may be quicker and seeds moved further if carried by animals along hedges. However, this role for hedges should not be overstated as there is not much evidence that hedges are critical for the spread of woodland plants from one site to another (Davies & Pullin 2007).

The hedges behind my childhood house in Essex dated from the early to mid-19th century. They had been created to divide up riverside grazing and meadows into separate paddocks, only for the hedges to be taken out again in the late 1970s to make one huge wheatfield. Clearance of hedges, alongside the piping of streams and ditches to create larger fields, was one of the most visible and contentious changes seen in the countryside in the post-war period (Peterken & Allison 1989, Norton et al. 2012).

Hedge removal may not have had major effects on the overall distribution of woodland plants because those in hedges tended to be the commoner ones anyway. However, it thinned their distribution through the countryside and reduced the nectar and pollen available to invertebrates from species such as Hogweed, Cow Parsley, Bramble and Ivy. In recent decades hedge clearance has slowed and new (in some cases replacement) hedges have been established under agri-environment schemes. It will take some decades before these acquire the same value for wildlife as those that were lost, although combining the hedge with sowing a flower-rich field margin will speed things along.

The 19th-century poet John Clare lamented the enclosure of common land, often through the creation of hedges as a tragedy, yet now clearance of those hedges is seen as undesirable from a conservation and a cultural perspective. So much of the general countryside has been impoverished, that small features such as verges, green lanes and hedges have become local hotspots for wildlife and protected by law. In a similar way, glades, rides and roadsides are hotspots for plants within a wood.

Nearly half the plant species in a wood may be found in rides and glades, even though they may occupy only 5–15% of the ground. The term ‘ride’ for the grassy tracks that separate the different blocks of woodland presumably arose because you could ride a horse down them, as opposed to the older, narrower paths where the canopy might meet just above a walker’s head. Many rides originate in the 18th or 19th centuries and were created to allow shots at game or views of a hunt. They are still important in woods managed for shooting today, but also to provide access to the timber crop.

Species often commoner in rides than under the tree canopy include Hedge Woundwort, Bitter-vetch Lathyrus linifolius, Common Figwort, Wood Speedwell and Wood Small-reed. More strictly confined to rides and wood edges are Wood Vetch Vicia sylvatica, Narrow-leaved Everlasting Pea Lathyrus sylvestris and Greater Burnet-saxifrage Pimpinella major. Ride and wood margins are also some of the best remaining sites for the rare Crested Cow-wheat in East Anglia. The woodland ride flora includes species also associated with ancient grassland such as Betony, Bloody Crane’s-bill Geranium sanguineum, Wood Crane’s-bill, Water Avens, Slender St John’s-wort, Adder’s-tongue Fern, Tormentil, Saw-wort Serratula tinctoria, Devil’s-bit Scabious, Ragged-Robin and Globeflower. In Suffolk, Lineage Wood was actually notified as a Site of Special Scientific Interest in 1971 in part because of the rich unimproved neutral grassland in its rides. The rides have become narrower, and the grassland more rank since, but there are still many species typical of the False Oat–Yorkshire-fog grassland type. In other parts of the wood, glades created by the removal of conifers planted during the 1950s and 1960s now include Bee and Pyramidal orchids (Orchis apifera, Anacamptis pyramidalis).

Wide rides where at least part of the vegetation receives direct sunlight at some time during the day are usually richer in plants and insects than narrow ones where the tree canopies meet overhead. Rides running east–west receive more sunlight for a given width and so again tend to hold more species than those running north–south. Rides need to be kept open and the vegetation cut regularly, preferably with the cuttings removed to avoid the build-up of nutrients that favour tall competitive species at the expense of the smaller grassland and woodland herbs. Detailed prescriptions have been developed for cutting the different zones along a ride (Warren & Fuller 1993).

The centre of the ride should be kept quite short with patches of bare ground by means of annual or biannual mowing. This gives opportunities for low-growing annuals such as Field Pansy, Corn Mint Mentha arvensis and Field Forget-me-not. Outside this may be a zone, cut perhaps every other year, of taller grasses (Cock’s-foot, False Oat and Yorkshire-fog) and herbs such as Marsh Thistle, Hemp-agrimony and Meadowsweet. This tall, rather scruffy vegetation is referred to on the Continent by the much more interesting titles of Mantle or Saum vegetation. Giving it a proper name helps emphasise this zone’s importance as a source of food and shelter for a wide variety of species, from bees on the Knapweed Centaurea nigra to leafhoppers sheltering in the grassy tussocks. Between the Mantle and the main tree-crop may be a zone of shrubs and Bramble cut every three to four years.

Peter Buckley and colleagues at Wye College in Kent studied how these different zones developed when previously narrow rides were widened (Buckley et al. 1997). There was an initial increase in plant species richness, often with double the number recorded in new ride-side quadrats compared to those taken under the shade. The additional species, such as Rosebay Willowherb, were mostly associated with disturbed ground. Over the course of a few years, species richness declined as perennial grasses became more dominant, along with tall herbs and scramblers such as Nettle and Bramble. Deer grazing promoted the increase in grass cover in some woods. More shade-tolerant woodland species such as Bluebell, Dog’s Mercury and Yellow Archangel survived where the shrubs were cut and allowed to regrow as a sort of coppice.

Ditches along the edges of rides help to keep them passable to forestry traffic, but also add to the variety of conditions and plants present. In Bourne Woods in Lincolnshire the ditches have Ragged-Robin, Great Horsetail, Yellow Loosestrife and Square-stemmed St Johns-wort. Deep ruts in rides formed by heavy vehicles can subsequently fill with water, forming temporary pools with Duckweed Lemna spp., Water-starwort Callitriche stagnalis and patches of Water-pepper Polygonum hydropiper. If they last long enough, they may provide breeding sites for frogs and attract dragonflies. We could view such ruts as a modern analogue of wallows created by Wild Boar, Red Deer or Wild Ox.

Maintaining the different cutting regimes across a ride can be difficult even on National Nature Reserves. Other priorities or budget cuts mean that the mowing is not done some years. Heavy deer browsing may frustrate efforts to develop the gradation of vegetation heights from the centre of the ride out to the tree zone. Spread of competitive grasses, such as Wood Small-reed, can reduce the abundance of flowering herbs.

Wood Small-reed Calamagrostis epigejos – a clay forester’s nightmare

This tall grass, with leaves up to 2cm wide and 1m long, occurs in Great Britain mainly south-east of a line running roughly from the mouth of the Humber to the Severn, on a wide range of soils, being tolerant of both waterlogging and drought. It is present through most of the rest of Europe but becomes more scattered in the north, on a range of habitats from sand-dunes, meadows and open ground in heavy-clay woods (Jefferson 2006, Rebele & Lehmann 2001). The grass can also tolerate various forms of pollution and has been used on the Continent in land reclamation projects.

Wood Small-reed spreads by underground stems. In clear-fells and ride verges it can form dense stands up to about 1m tall. The feathery flowering heads are quite attractive en masse and it is the food plant for two rare Wainscot moths and a range of flies and bugs. However, dense stands can cover several hectares and are quite species-poor. Young trees, whether planted or naturally regenerated, struggle to grow amongst it. Fortunately, it is not very tolerant of shade, so that once the young tree or coppice growth does start to close canopy the Small-reed declines.

Wood Small-reed may have become more widespread since the 1960s. It is favoured by increasing levels of nitrogen deposition from atmospheric pollution and there are more reports of it invading dry heathland and acid grassland. In semi-natural grassland across the Continent its increase has been linked to reduced levels of stock grazing. Wild Boar eat the underground stems, disrupting dense stands, but as they are not yet in the Midlands Clay Belt of England where Small-reed is most abundant, we cannot say whether they would be effective in its control there.

Wood Small-reed developing at the ride edge.

During the 1970s and early 1980s conservationists found themselves in a quandary. We were trying to stop ancient broadleaved woodland being felled and replanted with conifers (with some success). However, some of the best sites for butterflies and other sun-loving insects were precisely those sites that had suffered the most drastic forestry treatments, such as Bernwood Forest east of Oxford. The felling and restocking had created lots of open flowery rides, rich in butterfly food plants and sources of nectar (Sparks et al. 1996). Not without some soul-searching, Bernwood Forest was designated a Site of Special Scientific Interest, conifers and all.

Many insect species that were formerly common in coppice colonised the rides of replanted woods, because these provided a similar range of open scrubby conditions rich in flowers. On some sites, as the planted trees grew, the rides became too shaded for the plants to flower and the insect richness declined. However, at Bernwood, a change in forestry policy meant that the conifers are being removed to leave an Oak crop, and a stated priority for the Forestry Commission is to encourage butterfly food plants throughout the forest.

A study of butterflies using woodland rides in the Wyre Forest found they particularly liked feeding on thistles and yellow dandelion-like flowers; Bramble, Bugle, Heather, Self-heal and buttercups also came out well (Tudor et al. 2004). Some insects fed across the range of available species; others focused on just one or two. Some less-favoured plant species overall were nonetheless important as food for particular butterfly species; for example, Lady’s Smock was used by only 12 butterfly species compared to 42 using brambles, but Lady’s Smock was critical as a food plant for the Orange-tip butterfly.

The association of woodland butterflies with rides has proved convenient when it comes to monitoring their abundance in woodland. A standard method developed in the 1970s involves the surveyor walking a long a fixed route and counting how many individuals of different species were seen (Pollard & Yates 1993). A similar methodology has recently been adapted for studying bee populations, often in association with setting up bee hotels (collections of small tubes of different sizes bundled together) to attract solitary bees and wasps.

Hedges and rides take on another role when considered in relation to the development of new woods, which form the topic for the next chapter. Hedges can provide a local source of woodland plants for adjacent plantings. Conversely, rides may preserve remnants of the former vegetation. Breckland plants such as Candytuft Iberis amara and Wild Mignonette occur amongst the disturbed ground along the rides in Thetford Forest. In the big upland plantations of Sitka Spruce, rides and road edges contain a higher cover and diversity of species than the stands themselves; a similar result was found in more recent studies of Irish plantations (Hill 1979, Smith et al. 2007).