Hedges are more than just lines of shrubs. They usually have some sort of herbaceous growth at or near the base and many contain mature trees. They may be set on banks and can have ditches along one or both sides. Some have wide margins, often referred to as buffer strips or headlands, which are managed differently from the arable or grass crop.
It is important that all these different components; shrub layer, mature trees, base/bank, ditch and margins are considered when deciding how to manage a hedge. About two-thirds of Priority Species make significant use of at least two hedge components, and one-third three components or more.
Hedges can buzz with activity during the summer months and often provide a fascinating interlude for even the most casual observer of wildlife. Single trees provide song posts for yellowhammers and goldfinch-es, and assembly points for some butterflies. The flowers provide nectar and pollen for the bees and hover-flies that pollinate flowers (including those of commercial crops). Scrubby components provide nesting sites for many birds and even the delightful dormouse.
The base of the hedge and adjacent field margins pro-vide breeding sites for a huge array of animals, from bumblebees to hedgehogs and grass snakes. Each uses a slightly different structural component such as grass tussocks, protective accumulations of twigs and branches, and even bare exposed soil in which to bur-row. Nature will find a way of using what at first appears to be of little value!
What is more, hedges and their associated banks, field margins and ditches support huge numbers of common insects that form the essential diet of the birds, mammals, reptiles and amphibians that make the hedge their home or feeding grounds.
Bumblebees feed on pollen and nectar from shrubs and trees in the spring and from flowery margins in the summer. They nest and hibernate in the base of the hedge or in tussocky grass margins. When they move around the countryside, between their nests and food supplies, they follow hedges rather than cross open fields, so benefit from a network of connected hedges. All these elements need to be in place for the bees to thrive. If they do well then through their pollinating activities shrubs like blackthorn and hawthorn will produce more berries, which will in turn feed birds like wintering redwings and fieldfares.
The yellowhammer, like many other farmland birds, nests in the shrub layer or basal vegetation of hedges and feeds its young on invertebrates caught in flower-rich margins. They seek refuge from predators and adverse weather in the shrubs, and use trees as song posts. In the winter, seeds in the field margins form a valuable part of their diet. Once more, we see that several hedge components need to be present for a species to thrive.
The five components of a hedgerow
Shrub layer: The woody part of the hedge consisting of bushes, which are usually multi-stemmed and much branched, together with young trees, and is less than 4m high.
Tree layer: The woody part of a hedge which is normally more than 4m high, but may also be represented by substantial shorter pollards and coppice stools. Both isolated trees, where the canopies do not touch, and lines of trees are included here. Isolated trees usually have a single stem and are at least twice the height of the any shrub layer. Lines of trees may or may not have a shrub layer beneath them. Includes ancient trees and those with veteran features (e.g. deadwood, rot holes, splits and sap runs).
Base: The bare or vegetated ground beneath the canopy of the shrub and tree layer, where any perennial plant communities are at least partly shade tolerant. Includes any bank, but not any ditch. Banks may be turf or stone faced, and may support herbaceous vegetation or be bare, in whole or in part.
Margin: The ground adjoining the base towards the field centre. Include grass buffer strips, arable conservation headlands and field margins managed to benefit biodiversity, whether it be, for example, rare arable plants, bees and other insects dependent on nectar and pollen, or farmland birds. Margins will normally be managed differently from the main cropping or grazing area of fields. They may extend a considerable distance away from the hedge; no cut-off point is given, reflecting the main aim of the research to explore interactions between components, not their comparative importance to biodiversity.
Ditch: Any watercourse closely associated with the hedge. May be shallow or deep, and carry water permanently, seasonally or just in response to heavy rainfall events. Ditches may be under the canopy of the shrubs or trees or outside this line. Hedge banks are often formed from the material excavated from ditches.
The different uses of the components
Growing substrate: The hedge soil, leaf litter, twigs, branches or stems upon which fungi, lichens or plants grow.
Food: The use of the hedge as a source of food, whether for larval or immature stages or for reproductive adults.
Breeding: The use of the hedge for reproduction including finding mates, nesting/oviposition and provision of food for larvae. (For most invertebrates where larvae use a hedge for food the species concerned will also use it for breeding).
Shelter: The use of the hedge specifically to provide protection against adverse environmental conditions or predators, both for both active and dormant individuals. Includes the provision of hibernation sites (e.g. for some mammals) and overwintering sites (e.g. for insect eggs, larvae, pupae or adults).
Landscape connectivity: Some species populations have a significant dependency on more or less intact hedge networks, for commuting movement to and from food sources and breeding sites, or for dispersal.
The comparative importance of each type of component in supporting priority species and farmland indicator species
|Component||Number (%) species using specified component either on its own or with other components|
The great majority (81%) of species with a widespread distribution are dependent on more than one component. These include all farmland biodiversity quality indicators (comprising various butterflies, birds and bats). These largely comprise species that are representative of the agricultural landscape. In contrast, over half (57%) of species with a more restricted distribution are dependent on just one component on the basis of current knowledge. They are largely species that occupy highly defined and specialist niches.
The number of species using one, two, three, four or five structural hedge components, and the relationship between distribution (widespread or restricted) and number of components used.
|Component combinations||Number of species||% of all species||Number of species with restricted distribution (% of total number of species with restricted distribution)|
|1 component only||37||35%||25 (57%)|
|2 components||33||31%||13 (30%)|
|3 components||27||25%||5 (11%)|
|4 components||6||6%||1 (2%)|
|More than 1 component||70||65%||19 (43%)|
|More than 2 components||37||35%||6 (14%)|
|More than 3 components||10||9%||1 (2%)|
The information above was extracted from Understanding the combined biodiversity benefits of the component features of hedges, a Defra funded research project (need to upload and provide link to this on research page).
The importance of hedge trees
Hedge trees are traditionally part of the UK landscape and havens for wildlife. Yet, of an estimated 1.8 million hedge trees, nearly a third are over a century old and may disappear from the landscape at any time over the next 25 years. Without an immediate effort to establish new hedge trees, there will be profound changes to the UK landscape and its biodiversity. Since the late 18th century the abundance of hedge trees has dramatically declined. Periodic changes in farming techniques and agricultural needs, increased use of machinery, hedge removal, Dutch elm disease, neglect and lack of replacement have all taken their toll on the hedge tree population.
Why hedge trees matter
Hedgerow trees are important for several reasons. In the past they were highly valued for timber and with changing emphasis on renewable energy may once more come be useful for fuel. In livestock areas they are significant for shelter and shade, especially so as the climate changes and our summers become hotter, our winters wetter and we have more storms and gales. They are of great importance for wildlife and in some parts of the country they are notable as a source of fruit and other ingredients for food and drink. Trees in hedgerows often also screen eyesores and unsightly developments, and can protect privacy. Many of our most valued landscapes are dependent on hedgerow trees; without them, huge tracts of countryside would be bleak indeed.
The hedge tree population
In ancient hedges trees were selected and grown for a variety of specific uses. Oak, ash and elm were grown for timber amongst other purposes and appear to have been the commonest hedgerow trees. Willows and poplars were also frequent hedge trees and these species were often pollarded. Some minor trees species including field maple, aspen, holly and hornbeam also appear to have been specifically grown in hedges. In some places beech became a widespread hedge tree, and Exmoor’s landscape is famous for its 19th century beech hedges.
Along with timber species many fruit trees were also grown such as crab apple, wild cherry, hazel, elder and wild pear. These trees provided food in the autumn when other food supplies were beginning to run short.
Britain’s hedges contain an important collection of mature, over mature and ancient trees. In fact 30% of the hedge tree population is over 100 years old (CS2000). Part of the reason for this is the historical management they received. One of the main management techniques employed historically has been pollarding, which involves cutting the crown off a young tree at around 1.8-4.5m (6 to 15 ft) from the ground leaving behind a permanent trunk. Pollarding retains the tree in a state of greater vitality by interrupting the normal aging process and, since the crown is smaller, reducing the likelihood of storm damage. Pollarding trees has therefore allowed many to grow for several hundred years and some for much longer.
Why hedge trees are important for wildlife
Hedge trees provide a whole range of habitats in one small area. Together with the hedgerow, they provide shelter, food, nesting sites, song posts and hiding places, as well as stepping stones between woodland habitats. Many farmland birds use hedgerows trees: buzzards build their nests in the canopy, while woodpeckers and tree sparrows breed in holes. Bats, including rarities like the barbastelle and Bechsteinâ€™s, roost in crevices and tree holes. The trunks of veteran trees can support rich lichen communities. Butterflies like hairstreaks may be seen foraging for honey dew from aphids and laying their eggs high up in oaks and elms.
Rotting wood in living and standing dead trees within hedges is especially important for providing habitats for a wide variety of dead-wood beetles such as the lesser stag-beetle (Dorcus parallelpipedus) and others, some of which are very rare.
How to establish new hedge trees
There are several ways of establishing new hedge trees. You can select existing saplings (or promising coppice re-growth) already in the hedgerow; plant trees in existing gaps; create new gaps in which to plant by cutting notches in the hedgerow; plant trees beside the hedgerow rather than within it; or earmark saplings in a new hedgerow to become full-grown trees. Do think carefully about overhead services such as power lines which may cause future problems, and the risk of obstructing roads, tracks and rights of way.
When looking for existing saplings, select ones that are growing straight up all the way from the base. This should produce a good strong trunk if protected from cutting. Trees grown from stems that have been flailed, laid or coppiced may be so badly damaged that they are weak and unstable when mature. Itâ€™s often easiest to select and protect suitable saplings at the same time as laying or coppicing a hedgerow.
Many hedgerows will not contain suitable saplings, particularly dense single-species hawthorn and blackthorn hedges. Here it may be better to plant trees in gaps. Use existing gaps if possible because there will be less competition from existing plants. Otherwise, plant into a notch cut into the hedgerow.
Planting trees beside hedgerows may take up more space, but has the benefit of increasing the hedgerow width and its wildlife value. It may also be easier to cut the hedge in the future. There will be less root competition for nutrients and water, so the trees will probably grow faster. However, avoid planting trees on valuable habitats such as herb-rich grassland.
Planting trees when creating a new hedgerow is a very effective way of producing new hedge trees. Ideally, use species which are already growing in the locality, and invest in sturdy plants. Stakes or other supports are now only considered necessary for trees which are more than 1m tall and only for their first year. Once planted, use a marker stake and tree tag if necessary, to help prevent the trees being cut along with the rest of the hedgerow.
The Tree Council’s Hedge Tree Campaign
With urgent action needed to establish new hedge trees and prevent greater changes to the landscape and its biodiversity, The Tree Council, in partnership with Network Rail, is leading the Hedge Tree Campaign to increase awareness of why hedge trees matter and to halt their decline.
To champion the cause of hedge trees, the Tree Council is enlisting the support of its 7,500 volunteer Tree Wardens throughout the UK, its member organizations, local authorities and other supporters including farmers, landowners and contractors who are key to the success of the campaign. As many members of the general public as possible are also being encouraged to become involved.
The campaign will help to achieve the targets of local and national Biodiversity Action Plans for hedgerows. It will also help to maintain the overall number of hedgerow trees, estimated to be 1.8 million in Great Britain, through ensuring a balanced age structure. One way to ensure that there are hedge trees in the future is to mark newly-planted trees or existing saplings with easy-to-see tags. This will help whoever cuts the hedge to avoid the tagged young trees, allowing them to grow to maturity.
For more information visit The Tree Council’s website at www.treecouncil.org.uk
For more detailed information about hedgerow trees including how to establish them refer to our Hedgerow Trees Leaflet.