I have been taken to task for some of my previous remarks about exotics.
For example " How do you justify the assumption that a preference for
indigenous flora is purely "emotional" and without rational basis".
Actually I don't believe I said anything remotely like that but in case
what I wrote is also obscure to others; part of the arguments for and
against exotics are emotional. Nothing wrong with that in itself, this
would be a dull world if we never got excited about something now and
again, but this emotional preference for or against exotics makes the
subject a difficult one to handle in a calm and objective way. I gave the
example of the annual Canberra Floriade to illustrate the point that what
some people love others hate; with equal intensity. When you are trying to
make a decision about forest management these emotions are usually not very
helpful. They may be the deciding factor of course if an issue comes to a
vote in a system where democracy prevails. What makes people vote yes or no
is usually left for the individual to decide. I think most readers can
recall examples where a political decision has been influenced by what they
consider to be the will of a majority (or a vocal minority), which in their
opinion was wrong but was a response to deeply and genuinely felt emotion.
That is not what I thought the question implied, I was trying to make a
comment on the complexity of the issue and the difficulty of separating
emotion from the things you can add and subtract.
The flora of each country depends a lot on its political boundaries, its
geography (latitude, longitude, altitude) and its biographical history,
things like its physical separation from other land masses, occurance of
ice ages, rainfall patterns, not to mention the effects of humans and their
cultural practices. (There have been people in Australia, lighting fires
for about 50 000 years and this is widely thought to have influenced the
floristic composition of the continent a great deal.) None of this
guarantees that any country has received the optimum mix of plants and
animals. It is a common enough phenomenon to find that an exotic,
introduced into a new environment will perform with a greater productivity
than in its own country or in comparison with species indigenous to the
region. If this increased productivity is perceived as detrimental we call
it a weed ( European gorse in NZ), if we perceive it as beneficial we
congratulate ourselves on our wisdom. Radiata pine is a good example of the
latter case. This has very little to do with "the maintenance of diversity"
as such but may be relevant to that issue if the introduced species so
dominated the new environment that it eliminated one or more native
species. I doubt that radiata pine has eliminated any species anywhere it
has been introduced but I concede immediately that I am no expert on that
matter.
One of the messages I have received mentions that sheep may be detrimental
to rangeland, that the way some people in Australia grow sugar cane and
pineapple results in loss of topsoil. This is quite correct. BUT the title
of this discussion is costs and benefits. I don't pretend that the case for
or against exotics is totally one sided. Usually both costs and benefits
will be present. What I still assert ( as my strongly held opinion) is that
radiata pine, sheep, sugar cane and pineapple are success stories in
Australia, ie the benefits outweigh the costs. I agree that we might
increase the benefits if we removed sheep from some rangelands and planted
pineapples on the contour not straight up and down the slopes to suit
machine collection of the crop.
In 1955 The New Zealand Government engaged an emminent Canadian pathologist
to visit that country to report on the safety of its plantations of radiata
pine. This concern was stimulated by attacks of the wood wasp Sirex
noctilio. The resulting report by J.J.de Gryse states "to ignore the
notorious susceptibility of P. radiata to attack by insects and fungi, the
extreme vulnerability of the extensive monocultures in which it occurs, or
the astounding aggressiveness of radiata under NZ conditions is tantamount
to challenging all the laws of nature". The foretold disiaster has in fact
not happened. The fact is that this exotic tree is the predominant timber
tree in New Zealand and of immense importance in Australia where it has
been grown, as an exotic for about 150 years. It hasn't been all plain
sailing for that time but to deny its overall sucess would be quite wrong.
Ryde James.
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Ryde James | Forestry/Science
Tel: (61+6)249-4330 | Australian National University
Fax: (61+6)249-0746 | Canberra, ACT 0200
|
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email: Ryde.james@anu.edu.au
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