Traffic in plants and plant seeds

[John Grehan]

Paul Cherubini wrote:

At 06:46 PM 9/18/98 +0000, you wrote:
>Today over 90% of the 40 largest overwintering sites for the monarch
>butterfly (a butterfly native to North America) along the California
>coast occur in ornamental/agricultural plantings of exotic eucalyptus
>trees. 
>
>Good thing for the monarch that plant bigotry was not in vogue in the
>late 1800's when these trees were imported from Australia.

I am curious to know what the intention is here. Is Paul saying that without
eucalyptus the monarchs would have had nothing else to roost on because
people would have not planted anything else? If people did plant local species
there would perhaps have been no need to introduce eucalyptus?

Unelated in some way, but I recall that in some places (parts of Africa I
think)
eucalypts have been planted as the expense of local species, but the
eucalypts have been so efficient (if that's the word) at water intake that 
the surrounding areas have suffered water depeletion and consequent 
reduction in the survival of other species (this is just recollection so I'm
happy to be corrected).

Sincerely, John Grehan