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permaculture - Re: all theory thread DESIGN PRINCIPLES used in our course not

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  • From: Bob Howard <rmhoward@omninet.net.au>
  • To: permaculture <permaculture@franklin.oit.unc.edu>
  • Subject: Re: all theory thread DESIGN PRINCIPLES used in our course not
  • Date: Mon, 04 Sep 2000 08:44:36 +0800


Interesting discussion on weed/pioneer species. One point to bear in mind is
the
difference between 'native' and 'altered' landscapes. In Australia many of the
landscapes are substantially 'native' - that is they are dominated by endemic
species.
The AUstralian flora is substantially diffrenet from other flora's (and
fauna's).
HOwever this is not true throughout the continent. Road verges are a good
indicator - in
West Australia these are corridors of native species and substantially
uninvaded by
exotic weeds. Main Roads and many local governments here have a policy of
controlling
exotic species and replanting local species.

Contrast this with Westerrn Victoria - the only sites that retain the
original plains
vegetation are found in a couple of railway crossings near Melbourne. Road
verges in
Western Victoria are 100% dominated by exotic species.

The introduction of exotic( i.e. new) species to either of these landscapes
requires
different assessments.

There are weed (vigorous, invasive) species in both these environments. The
rate of
invasion depends also on the rate of disturbance in either landscape and upon
the
availability of niches within the environment. Undisturbed roadside habitats
will
persist with few to minimal weeds without being invaded by plants from
surrounding
farmland or disturbed areas because the available niches are all occupied.

Therefore it is not so much the vigorousness (or exoticness) of the species
per se that
matters but whether it can exploit a niche in space and time in the
surrounding
landscape that will determine it's rate of spread.

Lastly, one should bear in mind the definition of the weed as "a plant for
which no use
has been found. yet".Pc's prescription of 'weed' (i.e. pioneer) species has
always been
posited upon the species being useful. It seems logical to suggest that the
way to
assess a plant that may be 'invasive' is to ask what uis it's use and is it
really going
to be used.

Regards
Bob Howard
Albany W.A.









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