What Is a Hedgerow? A Linear Woodland With a Job

The value comes from structure rather than from any single species, since a hedge provides several habitats stacked together:

• •A dense woody core giving nesting cover safe from most predators, which is why hedges support high densities of breeding birds
• •A flowering layer providing nectar and pollen early in the year, when little else is available, which matters for bumblebee queens emerging from hibernation
• •Autumn fruit, with haws, sloes, hips, blackberries and elderberries feeding birds and mammals through the period when they must build reserves
• •A base of rough grass and herbs, which supports invertebrates, small mammals and the predators that hunt them
• •Dead wood and cavities in older hedges with mature trees, supporting fungi, beetles and roosting bats
• •Connectivity, since a hedge links woodlands across otherwise open farmland and functions as a corridor along which animals move, which is its most important landscape role

Hedges have several distinct origins and the differences are readable on the ground. Some are ancient, being remnant strips of woodland left when land was cleared, which is why a few carry woodland ground flora that does not colonise new hedges. Many were planted as boundaries over centuries of piecemeal enclosure, following field shapes that developed gradually. An enormous number date from parliamentary enclosure in the eighteenth and nineteenth centuries, planted as hawthorn in straight lines to fence newly allotted fields, which is why those hedges are geometric and species-poor. Hooper's rule, proposed in the 1970s, suggests that the number of woody species in a thirty metre stretch approximates the age of the hedge in centuries, which is a useful rough guide with well-known exceptions, since planting mixtures, soil and management all confound it. Combining species count with documentary evidence and with the presence of woodland indicator plants gives a much better estimate than any single method.

Britain lost a very large proportion of its hedgerows during the second half of the twentieth century, with estimates of removal running to hundreds of thousands of kilometres, driven by grant-aided field amalgamation to accommodate larger machinery and by the shift to arable in regions that had been mixed. The losses were substantial enough to change the appearance of whole counties. Legal protection arrived with hedgerow regulations in 1997, which made removing an important hedgerow without permission an offence, with importance defined by criteria including age, species and archaeological or historical associations, and the regulations have been criticised as complex and weakly enforced. Removal has largely stopped and a different problem has replaced it: neglect and inappropriate management, since a hedge that is flailed hard every year becomes a thin line of stubs with no flowering or fruiting wood, and one that is never cut at all grows into a line of trees with gaps beneath, and both lose most of the habitat value.

The evidence on management is unusually clear and unusually ignored. Flowering and fruiting occur on second-year wood in hawthorn and blackthorn, so annual cutting removes precisely the growth that would produce blossom and berries, and research has repeatedly found that cutting every two or three years rather than annually multiplies berry yield several-fold at almost no cost. Cutting timing matters equally, since work during the nesting season is prohibited and autumn cutting removes the berries just before they are needed, so late winter cutting is preferred. Raising the cutting height incrementally rather than to the same line each year prevents the thickening knuckle of cut stubs. Leaving standard trees within the hedge provides structure that a uniformly cut hedge lacks. Periodic rejuvenation by laying or coppicing restores a hedge that has grown leggy. Agri-environment payments now fund several of these practices explicitly, which is the mechanism by which habitat value competes with the cost of doing anything other than the fastest possible flail.

A hedgerow combines nesting cover, spring nectar, autumn fruit, a rough grass base and connectivity between woodlands, which is why it supports so much wildlife on farmland. Origins range from woodland remnants to geometric hawthorn lines planted at parliamentary enclosure, and species count per thirty metres roughly indicates age in centuries. Britain lost hundreds of thousands of kilometres to field amalgamation, and the current problem is management, since annual flailing removes the wood that would flower and fruit.