Priority Habitat: Native Hedgerows
1. Encourage better management of hedgerows for wildlife.
2. Increase the number of hedgerow trees through planting in new and existing hedgerows and allowing existing trees to grow to maturity.
3. Rejuvenate existing hedgerows through the use of coppicing, laying and gapping up.
4. Increase the length of new hedge planting, especially on historic field boundaries, or linking existing hedgerows or other semi-natural features such as woodland and scrub.
Vision Statement: For a greater total length of hedgerow in good condition, and increased linkage of semi-natural habitats using hedgerows and their margins.
|1. To maintain the extent of existing hedgerows in the Durham BAP area.||maintain||km||9,600||2006|
|2. To increase the total extent of total hedgerows in the Durham BAP area.||expand||km||10,500||2006|
|3. To increase the total length of hedgerow in good condition in the Durham BAP area.||achievecondition||km||2,500||2006|
|4. To maintain the number and improve the age profile of isolated hedgerow trees in the Durham BAP area.||maintain||number of trees||68,000||2006|
A hedgerow is defined as any boundary line of trees or shrubs over 20m long and less than 5m wide, provided that at one time the trees or shrubs were more or less continuous. (Hedgerow Survey Handbook).
Hedgerows are important in their own right as habitat for common farmland species, particularly butterflies and moths, farmland birds, bats and small mammals, which increasingly depend on them for food, and shelter in intensively managed agricultural landscapes.
For some species they also act as a vital movement corridor between areas of other semi-natural habitat.
Individual hedgerow trees are an important wildlife component of some hedgerows, providing roosting and nesting sites for bats and many birds, including tree sparrow, particularly as they get older (see Veteran Trees Action Plan).
The majority of hedgerows in Durham date from successive periods of enclosure between the 16th and 19th centuries. Most lowland hedges date from the enclosure of village townfields by private agreement in the 16th and 17th centuries. Those in the pastoral uplands and upland fringes were largely created during the enclosure of commons under the 18th and 19th century parliament enclosure acts. More ancient features such as medieval parish and township boundaries are scattered thinly across the area.
In many parts of the UK species-rich hedges are generally associated with ancient hedgerows. Indeed a common method for dating hedgerows is to measure the number of woody species in a 30m length. This methodology does not stand up in Durham, where known 16th Century hedgerows can be (woody) species poor, and more recent hedges relatively species rich.
The wildlife-value of a hedge is therefore only partly related to age (which might confer a more complex invertebrate or microrhyzal community for example), the more important biodiversity features of hedgerows being their condition, species richness and connectivity with other semi-natural habitats in the landscape.
Good condition for a hedgerow has recently been defined in the Defra’s Hedgerow Handbook in order to help monitor the status of hedgerows across the UK. Measuring condition includes an assessment of height, width and gappiness.
Hedgerows depend for their long-term survival on active management. In its absence most will gradually decline into individual lines of trees and shrubs. Neglect is the biggest problem facing hedgerows in Durham, and the length of hedgerows receiving no management has more than doubled to 63% since 1979.
However, much of the existing management does not lead to good hedgerow condition and will in itself lead to decline and loss of hedgerows in the long term. Many managed hedgerows in the Durham BAP are trimmed too regularly and too low.
Hedgerows are widespread within Durham except above the enclosure line in the uplands. Our most recent information comes from surveys in 1979, 1994 and 2006. The 1994 survey found that almost half the hedges on parish and township boundaries had been lost since 1856, or survived only as relics. Of the surviving hedges only about a third were being managed.
Hedgerow trees have also suffered a decline. The 1979 survey found that hedgerow trees occur around one to every 135m in lowland hedges. The number of younger trees that might replace older ones is also low. The ratio of small, medium and large trees in Durham hedgerows of 1:1:1 is below the recommended levels of 3:2:1, and it is estimated that to maintain the hedgerow tree population at its current level (68,000 in 2006) that approximately 580 trees need to be recruited into the hedgerow every year.
The latest survey results show that overall length of hedgerow has declined across the area. In County Durham comparison with the 1979 survey gave an estimate of a 21% loss of hedgerow length. Only 17% of the total hedgerow was estimated to be in good condition, the most common factor for failure being gappiness and a high basal canopy height. These are symptoms either of excessive trimming, overgrazing or neglect.
Although neglect can lead to highly valuable hedgerows with mature trees and shrubs, it will eventually also lead to the hedge losing its function as a barrier. In some cases this may presage removal. Neglect is now the biggest single threat to hedgerows in Durham
Although the Hedgerow Regulations (1997) prohibit removal of ancient and/or species rich hedges, other valuable hedges may fail to meet this definition. The protection of hedgerows also relies on the local planning authority interpreting the regulations strictly, and on landowners applying for permission in the first place. In Durham, it is thought that although a few hedges are being removed for housing development and road scheme, removal is not the biggest threat to hedgerows.
- Over-frequent and badly timed cutting
Over frequent cutting means that shrubs do not have the chance to bear fruit, and hence deprives other wildlife of a food source.
Cutting during the nesting season (from February to August) should always be avoided, and will disturb or destroy birds and their nests. It is an offence to intentionally take, damage or destroy the nest of any wild bird whilst it is in use or being built.
Over frequent cutting of a hedge to a small size allows no room for wildlife, and leads to a gappy and leggy hedgerow with little value for wildlife or use as a barrier.
- Use of agri-chemicals up to the base of hedgerows
Use of herbicide, pesticide or fertiliser on or near the hedgerow base will lead to loss of animal and/or plant diversity, and possibly the decline and loss of the hedge itself.