Hedgerows Habitat
Statement
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Summary
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.
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