| |
 |
We often hear conservationists speaking about ‘native’
species and extolling their virtues in comparison to their
counterparts – the so-called ‘non-native’
or ‘introduced’ species. But what do we really
mean when we describe a species as native?
The terms ‘native’ and ‘non-native’
are used to distinguish between those species, the natives,
which we believe would have been found growing in the United
Kingdom if humans had never been here, and those, the non-natives,
that appear to have arrived with a helping hand from us. This
‘helping hand’ may have been deliberate –
for example many plant species have been deliberately introduced
for cultivation as foods or ornamentals – or, in many
more cases, accidental.
There are numerous ways in which species may have been accidentally
introduced. Many farmland species, such as wild-oats and the
corn cockle, were quite probably introduced as impurities
in crop seed brought across from the continent, through trade
or in the supplies of invading forces. Some species may have
travelled from further afield as seeds in soil carried on
ships with deliberately introduced plants. When we consider
one suggestion that seeds may also have arrived in the padding
of horse collars, we begin to realise that the opportunities
for human-mediated transport are immense, and, with the burgeoning
of trans-global air transport, growing.
We can further divide the category of ‘non-native’
species into those which are ‘naturalised’ and
those which are not. Naturalised species are non-natives that
are found in the wild as self-sustaining populations –
they grow and reproduce successfully of their own accord.
By contrast non-naturalised species are either confined to
domestic conditions, such as gardens, farmland or plantations,
or only occur in the wild as direct escapes, with no self-sustaining
wild populations, in which case they are described as ‘casuals’.
Page 1of 2. Next: What
makes a native species important? >>>
|
|
