"Kay" wrote in message
...
In article , Des Higgins
writes

"BAC" wrote in message
...

I agree that being non-native should not, in itself, be presumed to be
bad.
What bad means in a particular context, of course, is a matter of
opinion.
Plants or animals which are potentially harmful can require careful
management, certainly.



The extremes are easy.
Take plants. In Ireland many species are not native but live happily in
parks and gardens or the wild.
One or two are a real pest though. These include Rhodendron ponticum
(wipes
out native oakforest),
Reynoutria x (cannot remember species or even correct spelling);
Heracleum
mantegazzianum (looks cool
but blisters skin and is invasive; can elbow out native species).

There I'd disagree. If it can elbow out native species, I'd regard that
as an argument for control. But not that it blisters skin. I think it is
for us to learn how to live around things, not to try to exterminate
things that might cause us harm.

These are
pests and I am quite happy to
get support getting rid of them. This is reasonabley clear cut. At the
other extreme are things like cornfield
weeds, some of which are very pretty and many of which are now very
scarce.
These used to be pests and are probably not native (some may be) but it
is sad to seem them go. You also get everything inbtween.

What about dandelions and nettles? Both of these seem to be getting more
abundant. Are they native?
Plantlife or some similar body does a regular survey which suggests that
things like dandelions and nettles are becoming more abundant at the
expense of the flowers (ladys bedstraw, birds foot trefoil etc) that I
remember as being abundant in my youth. I don't know that I'd consider
nettle as being a typical upland limestone plant, but a hell of a lot of
Yorkshire dales cave entrances are stuffed with them!
I'm not claiming any expertise here, just pondering aloud.

Otoh I read a report last week (Guardian? New Scientist?) of a study of
the effect of the Panama Canal allowing species to leak from atlantic to
Pacific and vice versa - the conclusion was that both sides showed an
increase in species richness, and there was no evidence that species on
either side had suffered as a result of the alien invasion. At least,
that was how the research was reported.

If you have not already read it, you might find
www.ben-network.org.uk/pdf/Vol4_5.pdf interesting, at least the first
section 'wildlife'.