I have to disagree with Paul Peake's point that "weeds do not enhance
biodiversity - they destroy it" (3 Aug 1998).
Rather than damn weeds outright, I feel that weeds should be considered
in the context of a given landscape, ie., its degree of modification and
its biota. I would expect that many naturalists could provide examples
of plant-animal interactions which involve plants declared as weeds and
native birds.
Consider the following simple example. A highly modified landscape (in
the eastern Mt Lofty Ranges, S. Aust.), ie., woodland converted to open
grazing for sheep with only a scattering of old eucalypts, has patches of
Gorse (Ulex europaeus) and blackberry (Rubus spp.) which provide dense
prickly-shrub type habitat utilised by birds such as Red-browed Finch,
Diamond Firetail, Southern Whiteface, Superb Fairy-wren, and
Yellow-rumped Thornbill. This is biodiversity in my opinion. Not ideal,
not what might have occurred there ~200 years ago, but biodiversity now,
in the area concerned. One land manager was about to remove an extensive
area of the above mentioned weeds using an air-tractor to apply
herbicide, but fortunately, when it was pointed out that the weeds were
providing locally important bird habitat, he agreed to 'tolerate' most
areas of the perceived weeds for the sake of the birds. The alternative
landscape in this case, ie., without the Gorse and blackberry, and
given the current land use and its management, would be rough
pasture,...by itself, not at all suitable for the avian species listed
above,...that is, a landscape with less avian biodiversity than at
present.
Obviously, there are examples of weeds undermining the integrity of
biotic communities and populations, and many require appropriate
treatment (possibly weed eradication), but the point I make is that weeds
do not neccessarily destroy biodiversity, they sometimes enhance
biodiversity by providing certain organisms with food or habitat
resources in landscapes otherwise devoid of such. There needs to be an
understanding and recognition of the important role that many so-called
weeds sometimes play in ecosystems which are highly modified by humans,
before we damn all weeds.
Marcus Pickett
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