The Ecology of Hedgerows and Verges Plants
Species composition of hedgerows and verges have an infinite variety where not only are no 2 the same, but they are different every 100 yards or sometimes every few yards. The situations they are found in vary almost as much. From a hedge between two fields of differing crops to riverside and canal hedges, from small road hedges and verges through to wide motorway bankings, railway embankments and narrow rock cuttings. With soil types of all kinds.
Added on to this, the management regimes can alter composition dramatically. i.e. regularly mown of grazed verges tend to favour finer leaved, shorter plants such as fescues ( Festuca spp) and common bent (Agrestis capillaris) as well as rosette species e.g. dandelion (Taraxacum officinale spp.), greater plantain (Plantago major) and creeping buttercup (Ranunculus repens). Whereas the absence of this mowing or only mowing in autumn or winter, encourages coarser grasses and taller plants such as cocksfoot (Dactilis glomerata), Yorkshire fog (Holcus lanatus), meadow buttercup (Ranunculus acris) and large umbellifers such as cow parsley (Anthriscus sylvestris) and hogweed (Heracleum sphondylium).
Besides these differences a few themes run throughout. Although not all hedges are on banks or have ditches and not all verges have hedges. Where ditches are present sometime they have running water, sometimes standing water used as a soak away or may even be dry ditches where the water only appears in heavy rain or runs underground.
Verges can often, depending on their size, be divided into 3 zones which can usually be very easily distinguished.
Found at the road edge and is usually no more than 6 inches (15cm) wide though occasionally can be larger, and is greatly influenced by pollution (usually saline, now that lead is not such a problem), compaction by pedestrians or vehicles and disturbance. As can be expected it has a characteristic flora and often include halophytes (salt tolerant plants).
The soil at some places has the equivalent saline level of a salt marsh, which has far to high a level of salt for most common grasses which will die out leaving bare patches, which are then in tern colonised by halophytic plants.
Also sodium is known to play an important part in flocculation of clay (the action of the small clay particles clumping together). Therefore improving the soil texture and crumb structure as well as aeration and drainage. However an excess of sodium causes the flocculation process to break down and once again the clay particles form a dense compacted and impermeable layer.
Typical species include; Greater plantain(Plantago major) , ribwort planatin (P. lanceolata) , pineapple mayweed (Chamomilla suaveolens), scented mayweed (Matricaria perforata), red bartsia (Odentites verna), creeping cinquefoil (Potentilla reptens), corn spurry (Spergula arvensis), daisy (Bellis perennis), annual meadow grass (Poa annua), perennial ryegrass (Lolium perenne).
Most verges are now mown off at certain times of the year. Some are only mown in autumn which does not impact to dramatically, however the majority of ‘A’ and ‘B’ roads are now mown twice. Once in June or July and then again in the autumn. Except for motorways and some ‘A’ roads, this usually consists of a 1 metre strip along the roadside edge of the verge which is increased, for safety reasons, in width at corners and junctions for visability. These extra cuts can go back all the way to the hedge and are known as sight lines.
The action of this cut on the verge is described above and often overlaps in inner and outer zones.
The inner zone is not under as much pollution pressure as the outer zone, nor tends to be walked or driven over so its flora can grow unhindered. Its width varies considerably and is in some places absent altogether, due to mowing, where the whole verge is 1 metre or less in width. Where it is in place, it can vary from 1 or 2 metres to 20 to 30 metres in some cases, but generally speaking, the further from the road then the more stable the environment will be and the greater the variety of the slower growing flora.
With the exception of when it is very wide, the inner zones humidity, light and soil conditions tend to be dominated by the hedge. This zone has a generally undisturbed environment for the plants growing there (management aside). The plants that colonise these areas will also attempt to spread into the outer zone but rarely survive for long.
Dominant and common plants in this zones are; hogweed (Heracleum sphondylium), cow parsley (Anthriscus sylvestris), mugwort (Artimisia vulgaris), common knapweed (Centaurea nigra), thistle (Cirsium spp.), silverweed (Potentilla anserina), wild carrot (Daucus carota), hawkweeds (Hieracium spp.), common toad flax (Linaria vulgaris), birds foot trefoil (Lotus corniculatus), field forget-me-not (Myosotis arvensis), goatsbeard (Tragopogon pratensis), campions (Silene spp), white dead nettle (Lamium album), yarrow (Achillea millefolium), clover (Trifolum spp.), timothy (Phleum pratensis) and smooth meadow grass (Poa pratensis).
Ditches are absent as often as they are present, dependant on the soil type and drainage structure of the ground. When they do occur then it tends to be nearly always on one side. Ditches may vary in size from a shallow gully that is dry most of the year, through permanent water filled ditches that may be flowing or may be standing water, to large dykes commonly found in the eastern part of England which can measure tens of metres across and behave more like small rivers and have enough current to keep themselves relatively silt free.
With permanent standing water
The standing water ditch resembles an elongated pond, with a layer of mud at the bottom which may become short of oxygen and smell quite foul.
The following plants are commonly found growing on dryer parts of the ditch bottom although they are quite used to the wet and muddy conditions. These include fools water cress (Apium nodiflorum), marsh marigold (Caltha palustris), meadowsweet (Filipendula ulmaria), brooklime (Veronica beccabunga), water forget-me-not (Mysotis scorpioides), water figwort (Scrophularia auriculata), watercress (Nasturtium officinale), water crowsfoot (Ranunculus aquatilis), starwort (Callitriche stagnalis) as well as duckweeds (Lemna spp.) which is the only one not to have roots in the soil but to be free floating.
The tendency for mud to accumulate in ponds, lakes and still water ditches, as plants die year after year and sink to the bottom, to rot and be broken down by the water borne invertebrates and bacteria, creates a situation where the water gets progressively shallower. The edges then dry out and cause the mud rooting plants to be replaced by more vigorously growing plants that share the dry ditch environment. This action is called Hydro sere, and if left unchecked will dry up the ditch completely. Where ditches are regularly cleaned out, however, this process is stopped.
Ditches which become dry in the summer but wet in autumn, spring and winter provide a very unstable environment for colonisation according to the vagaries of the weather and can go from dry hard ground to flowing flood sometimes in a matter of minutes in heavy rain and then back to dry ground again.
Very few plants, with the exception of horsetails, can survive these conditions and so end up rooting themselves on the firmer, dryer sides of the ditch but there are a few that manage to get a hold in the mud. Commonly found in these conditions are common comfrey (Symphytum officinale), which could even have a commercial interest due to its high protein content and is a food source of the scarlet tiger moth (Callimorpha dominula) which is one of the most striking of diurnal moths. Also found here are marsh woundwort (Stachys palustris), lesser burdock (Actius minor), hemp agrimony (Eupatorium cannabinum), winter cress (Barbarea vulgaris), marsh thistle (Cirsium palustre), common horsetail (Equisetum arvense), great willow herb (Epilobium hirstutum), marsh bedstraw (Galium palustre), hogweed (Heracleum sphondylium), and common valerian (Valeriana officinalis).
With permanent running water
The flora of running ditches are basically river living plants whose evolution has created then to be rooted in the substratum, or on the surface of stones with floating and/or submerged leaves, such as river water crowsfoot, starwort, Canadian pond weed and willow moss (Fontinalis antipyretica). At the water edges, mud areas are found that give rise to mud rooting plants as above.
Hedges are sometimes planted on banks of earth, especially at roadsides. These banks can range in size from several metres, where a road passes through a cutting to less than a foot in flat areas. Where a ditch is present, then the effects of the bank are increased on the ditch side.
Like verges the larger banks can be divided into 2 zones. The distribution between these two zones varies greatly in size, whether north or south facing, and with the flora of the verge inner zone or ditch.
The Lower zone
The lower zone tends to be dominated by the humidity of the soil (which tends to be relatively high if adjacent to a ditch, or low if adjacent to a road that is well drained.), and the organic matter from previous years plants. Possibly the greatest influence however comes from the shading effect of the hedge plants above, especially on a North facing bank.
If the soil conditions of the lower zone are quite damp then this will favour mosses and ferns as colonising plants with lords and ladies ( Arum maculatum) , harts tongue fern (Asplenium scolopendrium) , black spleenwort (A. adiantum nigrum), male fern (Dryopteris filix-mas), polypody (Polypodium vulgare), cut leaved cranesbill (Geranium dissectum), herb robert (G. robertianum), marsh bedstraw (Galium palustre), red campion (Silene dioica), rough chervil (Chaerophyllum tementum), lesser celandine (Ranunculus ficaria), creeping buttercup (Ranunculus repens), hedge woundwort (Stachys sylvatica), sweet violet (Viola odora), meadow fescue )Fuestuca pratensis), common st John’s wort (Hypericum perforatum), primrose (Primula vulgaris), bluebell (Endimion non-scriptus) , dandelion (Taraxacum spp.) and herb bennet (Guem urbanum).
The Upper zone
On the whole the upper part of the bank is drier than the lower zone, courtesy of the root systems from the hedge above, which can have a selective effect on the flora growing there. The plants found here are pretty much the same as those found in the inner zones of verges with the exception of the greater stitchwort (Stellar holostea) which tends to be restricted to hedge banks as its habitat.
The shrub and tree zone
As it sounds this section comprises of mainly woody stemmed bushes along with mature trees and saplings which are sometimes incorporated into the hedge.
However also sharing the environment are the climbing and rambling plants such as herbaceous white byrony (Bryonia dioica), hedge bindweed (Calystegia sepium), hop (Humulus lupulus), black byrony (Tamis communis), woody old mans beard (Clematis vitalba), ivy (Hedera helix), honeysuckle (Lonicera periclymenum), bittersweet (Solanum dulcamara) and brambles (Rubus spp.).
These plants root in the soil and then clamber or climb up through the hedge by means of either tendrils, like white byrony, which can be commonly seen on vetches and other pea family plants, or by twisting around the shrub stem as in bindweed.
Many species produce fruit which acts as an important source of food for birds and mice during the autumn and winter, complementing the berries found on the hedge plants themselves.
Common woody species found here are;
hawthorn (Crataegus monogyna) and or midland thorn, hazel, elder, dogwood, blackthorn, privet, holly, spindle, wayfaring tree, guilder rose, dog rose, field rose and as trees; field maple, ash, oak, elm, sycamore, crab apple, wild cherry, damson, beech, whitebeam, willow, mountain ash, birch, and chestnut.