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Contents
Walk on the wild side
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| Herring Gulls like this juvenile 'foot-paddle' to attract worms to the surface. |
David Harper and David
Streeter BIOLS
Autumn is now in
full swing. The two main ways in which plants cope with the winter is by
shedding their leaves or by stopping growth, so the grounds staff increasingly
face the chore of clearing fallen leaves rather than mowing the grass.
Virtually all of the thousands of trees on campus are deciduous, including one
of our three native conifers, Larch (one of which can be found on the
north-west of the Science Car Park). Our only common evergreens are the other
two native conifers, Yew and Scots Pine, and a broad-leaved shrub, Holly.
The natural
seasonal partner to Holly, at least in folklore, is Ivy. Our only evergreen
liane unusually has its main flowering period in the autumn. The clusters of
small yellow-green flowers are in bloom from September to November. Nectar is
produced on the surface of the central disc at the base of the prominent
stamens and is thus accessible to short-tongued bees, wasps and flies that
congregate in large buzzing crowds on sunny days. As well as feeding on the
nectar, wasps no doubt take advantage of the easy pickings from the range of
small insects that also gather at the feast. The flowers are produced only on
the mature shoots, which lack the familiar lobed leaves of the young stems that
trail along the ground and clothe the base of the trunks.
The dramatic
changes in vegetation during the autumn reduce the shelter and food available
to animals. Combined with the shortening days and worsening weather, they mean
that invertebrates on campus are rapidly becoming scarce. Most insects, for
example, spend the winter as eggs, larvae or pupae hidden in crevices or the
soil. Insect-eating birds therefore face a treble whammy: less food; shorter
days in which to find it; but longer, colder nights to survive.
By contrast,
some nocturnal predators such as Tawny Owls and Foxes are enjoying a food
bonanza. The lengthening nights coincide with the annual peak in small mammal
numbers. This year, Bank Voles are especially obvious, even by day, in the
bushier areas of campus.
Along with
voles, nuts and berries, autumn is the season of worm-casts! The amazing
landscaping abilities of worms were first highlighted by Charles Darwin in Vegetable Mould and Earthworms, where he
describes in extraordinary detail the part played by worms in converting the
leaf fall to humus. Surprisingly he failed to spot that the species that lined
their burrows with leaves were different from those that produce casts. In a
chalk valley on the North Downs in Kent similar to campus, he calculated that
the worms produced annually 18.1 tons of worm casts per acre! This gives some
idea of the food supplies available to any animal that can catch worms. Look
out for Herring Gulls 'foot-paddling' on lawns to attract worms to the surface.
Contents
Friday 2 November 2001
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