Hedgerows habitat statement

Hedgerows are linear features composed of woody species. Ancient hedgerows are those which were in existence before the Enclosures Acts (passed between 1720 and 1840 in Britain). Species-rich hedgerows are those which contain 5 or more native woody species on average in a 30 m length, as defined in Wicks & Cloughley, 1998. In urban areas many hedgerows are of relatively recent origin, having been planted along the boundaries of gardens, parks or open space around schools and other institutions. These hedgerows are frequently composed of non-native coniferous or evergreen species.

When the amount of documented native-species hedgerow is identified by borough, as a percentage of the total native-species hedgerow resource in London, it does give an indication of the distribution of this resource (see Table 1 in the full version of this Audit).

The hedgerows with most intrinsic nature conservation value are mainly those that predate the Enclosures Acts. Many of these hedgerows are remnants of ancient woodland, retained to mark boundaries. They consist of species such as hazel Corylus avellana, oak Quercus robur, hornbeam Carpinus betula and field maple Acer campestre and harbour woodland or woodland edge flora including bluebell Hyacinthoides non-scripta, primrose Primula vulgaris, wood anemone Anemone nemerosa and honeysuckle Lonicera pericylmenum. Hedgerows, as boundary features, are ecologically important for a diverse range of invertebrates. The orientation of the hedge can provide varied micro-climates and associated features such as banks and ditches create additional habitat diversity. As corridors, hedgerows allow species of small mammal such as wood mouse and bank vole to move between nearby wooded habitats. This helps to prevent local extinctions through the isolation of small populations. Bats will also use hedgerows as flight line features and the loss or fragmentation of the hedgerow can result in a reduction in a bat's range.

Old hedgerows are also important from a cultural perspective, often marking boundaries of historical significance or the line of historic green lanes and other rights of way.

Although of less intrinsic nature conservation value than the older native-species hedgerows, mixed and non-native species hedgerows around parks and gardens can provide nest-sites for common garden birds and habitat for a variety of common species of invertebrate as well as some that are rare or declining. The privet hawk-moth, for example, is now rare in London, despite the caterpillar feeding on garden hedgerow shrubs such as garden privet, lilac and forsythia.

Most old hedgerows in London, particularly in the arable farmland of the Green Belt or within the mostly densely urbanised parts of the city, no longer serve their original purpose as stock-proof barriers or markers of parish or property boundaries. Consequently they are subject to 'grubbing out' where their presence hinders agricultural operations, development or expansion of recreational areas - or neglect where they no longer delineate a recognised boundary. Even where a hedgerow may still prove useful as a stock-proof barrier (e.g. where livestock, particularly horses, are paddocked - a relatively common occurrence throughout London's Green Belt) it is often removed - either to expand the effective grazing area, or because of the difficulties of hedgerow maintenance.

The most prevalent form of mismanagement is flailing or cutting too frequently. Hedges which are cut or flailed to the same width and height on an annual basis rarely flower or fruit (depriving animal species of a food supply) and become too dense and compact to provide suitable nesting habitat for many birds. Conversely, a hedgerow that has not been managed (cut, coppiced or layed) for many years eventually loses the essential characteristics of a hedgerow and becomes a line of trees. This habitat is usually considerably less valuable to wildlife. Other commonly encountered examples of unsympathetic hedgerow management are mowing, spraying or ploughing vegetation at the base of a hedgerow; and filling gaps in native-species hedgerows with quick-growing conifers.

Hedgerows have become something a cause celebre, in part because of their historical associations and as symbols of a romanticised view of the English countryside. This cultural value of hedgerows ensures that there is considerable public interest in hedgerow conservation and protection.

Better hedgerow management in London's farmland and semi-natural open spaces can be promoted through targeted advice and incentive schemes such as Countryside Stewardship. The restoration of neglected hedgerows can also be addressed through incentive schemes linked to a growing interest in the traditional skills of hedgelaying and coppicing. Although never a replacement for existing hedgerows, new hedges can be planted and can be particularly valuable in restoring links between isolated areas of semi-natural woodland or scrub habitats.

Traditional hedgerows were a functional element in the landscape. Therefore, restoring a 'purpose' for hedgerows might prove an effective tool for ensuring the management and restoration of existing hedgerows and the establishment of new ones. The Metropolitan Police Crime Prevention Unit has advised that planting thorny hedgerows along boundaries provides a deterrent to burglars. Furthermore, establishing or restoring hedgerows along the boundaries of parks and other open spaces provides a visual barrier to the urban landscape and may filter noise and other pollutants. Hedgerow restoration and management can also be a catalyst for restoring neglected rights of way or re-establishing a sense of neighbourhood by rediscovering and redefining old parish boundaries.