There are three ways
that hedges have been produced.
Hedge-planting is
familiar and well documented; nearly all more ecent hedges have
certainly been planted. .
Hedges also arise
whenever a ditch, bank, lynchet, or earthen wall is neglected for a
few years not too far from a source of tree seed; a hedge will
result. Fences turn to hedges by birds sitting and dropping seeds;
the fence protects the incipient hedge.
Hedges arise in a
third way as the ghosts of woods that have been grubbed out leaving
their edges as field boundaries. The marginal trees, often already
forming a hedge to protect the wood's interior, may be left as a
hedge having woodland, rather than hedgerow,
characteristics.
There are three
hypotheses to account for the observation that older hedges have
more species:
1. A hedge acquires
further species as it gets older. Tree and shrub seeds are
constantly being brought by chance and birds. They germinate and
occasionally get established.
2. In earlier times
it was the custom to plant hedges with more species than later.
Enclosure Act hedges were generally planted with one species only,
usually hawthorn. As with other fashions, it is not easy to
determine why, but the large scale and commercial character of the
operation encouraged simplicity. Georgian enclosers usually planted
hedgerow trees; after the felling of the original trees the
regrowth of the stumps gives the hedge a second species. Victorian
enclosers often omitted the trees. Pre-Georgian hedges were often
planted with two or more species.
3 The older a
hedge, the more likely it is to be natural rather than planted, and
therefore to be mixed from the start. Both kinds of natural
hedge- ghosts of woodland boundaries and accidental hedges
springing from the base of fences- are unlikely to be specifically
documented; but conditions for them to arise have probably been
much less rare in the past than they are now.