What is a hedge?

Most hedges are lines of shrubs and trees planted to form a barrier between two portions of land. They define boundaries of land ownership, control stock animals, protect from wind, noise or prying eyes, provide biomass or simply look attractive. Hedges have incidental value for human foraging, from fruit and nuts to firewood, and help prevent flooding and soil erosion. They capture atmospheric carbon, and filter the air – and wildlife moves in.
Managed hedges are those where there is still some attempt to restrict the natural growth of the trees within them, whereas a relict hedge has been left to grow its own way and may remain as just a few spaced-out crooked trees on an earth bank or become a thick strip of trees and shrubs. 

In addition to these, Oliver Rackham identified the “ghost wood” and the “natural hedge”. The first refers to hedges that retain the outline of a wood no longer there. The species composition in this hedge will reflect its woodland origin rather than intentional planting. A natural hedge arises from neglect of a strip of land, such as along field margins or in ditches, that escapes mowing or grazing.

How do you age a hedge?

Ancient hedges date from medieval and earlier times; enclosure hedges date from the 17th and 18th centuries; and modern hedges are more recent. These support different levels of wildlife interest and merit different levels of protection. In short, the older, the thicker and the more tree species a hedge contains, the better.

In old maps, boundary hedges were often marked differently from fences. Enclosure hedges are dead straight and generally contain up to three tree species (mainly hawthorn and blackthorn) whereas older hedges usually have gentle curves and more species. Perhaps 80% of Britain’s hedges pre-date the enclosures.

Hooper’s Rule, an ecological calculation, broadly says the number of woody species in 30 yards is its rough age in centuries – so seven species suggests 700 years. This highlights that age  - including older trees -  is usually the most important factor in a hedge’s wildlife value. Grubbing out an old hedgerow and replacing it with even double the length of new hedge elsewhere will generally see a loss of biodiversity.
 

How useful are hedges?

All hedges can be important for wildlife, but some are better than others. A good hedge and its associated verge can support anything from ladybirds to nesting birds, from woodlice to harvest mice, from badgers to pollinators. Notoriously static species such as bluebell, wood anemone and primrose growing in a hedge indicate that it may have its origin as a ghost of ancient woodland. They also act as wildlife corridors, connecting small areas of habitat physically and therefore allowing them to support species that suffer in fragmented landscapes. Bats and moths may use hedgerows as scent trails between feeding areas, and the shelter from the wind allows easier travel.

Many declining farmland birds, including yellowhammers, corn buntings and linnets, nest in hedgerows along with dunnocks (once called hedge sparrows), chaffinches, bullfinches and great tits. Their breeding success in hedgerows may be as high as in decent woodland in good years. Good hedges – ones that are tall, wide, old, dense right from ground level and with a wide range of woody species – are vital for wildlife.

Helping hedges

Over 120,000 miles of hedgerow have been lost from the British countryside since the 1950s. To maintain the wildlife value of the remainder, hedges need to be managed.

Traditionally, this involves laying the hedge by hand every 10-15 years. The hedgerow trees are cut part through, bent over and staked. This reduces their height, improves their impenetrability and rejuvenates the hedge for wildlife. Local variations produce distinctive hedges. In Northants, for example, bullock style laying aims to control cattle rather than smaller lambs. Modern management usually involves a tractor-mounted flail or circular saw. It’s quicker but less sensitive, and needs to take place outside the April to August bird breeding season.

Because hedges are so important for wildlife but also so vulnerable, monitoring their extent and condition is seen as a vital tool in assessing the state of our wildlife. Check out the People’s Trust for Endangered Species (PTES)’s new hedgerow surveys and take part here: hedgerowsurvey.ptes.org

This article was originally published in the summer 2022 issue of our members' magazine Local Wildlife.

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