[permaculture] Are we a weed?
rmhoward at omninet.net.au
Thu Mar 27 07:40:04 EST 2003
Toby Hemenway wrote:
> I was interested in the possibility that one-way weed travel is just a myth, since people have cited a few counter-examples (though the examples are mostly of animals, which have very different dispersal systems than plants). I pulled down my copy of Ecological Imperialism: The Biological Expansion of Europe, by Alfred Crosby, and browsed around. He cites data showing that of 500 farmland weeds (plants) in the US, over half are from Europe, and in Canada, over 60% are European. Roughly the same numbers are found in Australia and S. America. But in Europe, less than 10% of the weeds are not from Europe or Asia. Not a single Australian or NZ weed was found in Europe until after 1920. The only major weeds in Europe from North America are two fleabanes, Canadian waterweed, and a handful of others. Most of the most aggressive US weeds, like ragweed, goldenrod, and milkweed, haven't gained a foothold in Europe. Yet roughly the same amount of shipping goes to Europe as from it, s!
> think just as many species have been imported both ways.
I agree with your point about guilds further down. The "before 1920" date is pretty significant for Australia. Many environmental weeds in Australia are garden escapes or deliberate releases. In Australia, in the 19th Century there was a naturalization movment that sought to introduce deliberately european plants and animals into Australia. The fox and the rabbit were both deliberate introductions as well as many plants.
The reason there are no australian weeds in Europe is emphatically that the traffic has all been one way. Not that tehre is any intrinsic virtue or virulence to the european variety. In australia some of the most destructive environmental weeds are from other parts of australia. Plants such as acacia saligna and hakea suavolens to name but two.The latter is a declared weed in south africa where it has become established in the wild as have a number of australian acacia species which have been deliberately introduced into Africa..
Again get over this obsession that there is something intrinsically virulent or virtuous about Europe. It's total garbage.
> Thus the (mostly) one-way weed establishment is a fact. One reason for this, in addition to those I cited in my last post, is that counter-directional species usually travel alone, separate from their guilds, while European weeds travel with their guilds: We bring cattle, sheep, and all the other animals that have adapted with Euro-weeds (which have burrs adapted for our livestock, pass through their guts unharmed, etc); we bring pollinators by the millions (European honey-bees love Euro-weeds), and we bring many of the other insect and plant associates that are allies of the weeds. That broad-band traffic doesn't go the other way, and thus non-Euro-weeds don't thrive. You could say they die of loneliness.
> For a look at my book on ecological gardening,
> Gaia's Garden: A Guide to Home-Scale Permaculture, visit
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