[permaculture] Exotic Species: #2 Cause of Extinction?

Bob howard rmhoward at omninet.net.au
Fri Jul 5 08:27:25 EDT 2002

Kirby Fry wrote:
> Hello,
> Has anyone heard the figure that exotic plant species are the number
> two cause of species extinction in the U.S.A? 

I'd like to know what you think is number one... I've always learnt that
habitat destruction is the most conclusive cause of local extinction. 

Species extinction has to be assessed on a species/habitat by
species/habitat basis. Habitat and species are for all reasonable
purposes inseparable. 

Habitat size and isolation are the primary determinants of extinction
risk. Small isolated islands with a unique species of flightless dodo's
are always primarily at risk. 

One should think of isolated patches of wild land as islands. As the
islands become smaller and more separated the risk of extinction

On islands the cause of extinction can be the invasion of a new species
and this in turn is due to some disturbance - the visit of a ship, a
wildfire, a new road or bushwalking track. 

Isolated islands get few disturbances but are highly vulnerable. Islands
close to other islands or sources of disturbances have a higher rate of
invasion etc. 

> My question, however, is how much money and time do we spend on exotic
> / invasive (including native invasives) species eradication? Has there
> ever been a species eradication project that didn't require perpetual
> maintenance?  Can exotics naturalize in a symbiotic manner?

The Bradley sisters in the Royal National Park in Sydney long ago
established three principles for bush regeneration that stand most bush
regeneration projects in good stead. These are a result of their
experience 'weeding' the National Park of exotics.

1. Work from the 'good' areas to the bad
2. Minimize disturbance
3. Work at a rate of natural replacement. i.e. don't weed faster than
the bush will naturally regenerate - fill the holes you've left.
Variations on this theme are pratcied to good effect by local councils
thorughout Australia.

This could be considered a practical Aussie feminist response to Fukuoka
- but I wouldn't dream of suggesting such a thing! :->


Bob Howard

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