invasive plants

I've just finished a graduate seminar on invasive plants, and there are
multiple factors involved in the process, none exclusively responsible for
success.  A few have already been mentioned and include things such as high
numbers of seed set, effective methods of seed dispersal, long-lived seed in
the seed-bank, aggressive growth habit, ability to multiply vegetatively,
ability to colonize disturbed habitats quickly.  Sometimes allelopathy is
involved, and of course, there is the absence of natural checks such as its
own native parasites and/or predators.  In addition, the invaded area may
have milder weather that allows the invader to live longer and produce more
offspring than in its native habitat.  If a waterway is involved, the issue
is complicated by the constant source of water and the ability to disperse
seeds long distances.  Very aggressive growers can displace more modest
natives.  A very interesting topic that has arisen is the idea that woody
species can take decades of establishment as ornamentals or isolated "weeds"
before becoming a truly invasive plant.  Only recently, figs have been
classified as invasive along some California waterways, though they have
been grown here since the time of the first missionaries. 
The kind of adaptation to environment alluded to in the article mentioned in
the previous email can hardly be termed evolution, as "ecotypes", or plants
of the same species more adapted to local conditions, have been known for a
long time.  This is really adaptation rather than evolution, as the species
hasn't yet changed.  I wonder how MUCH genetic variation there was between
their specimens.

The lesson we learn from invasives is to be extremely careful any time you
plant something very far outside its native home, especially if you are near
waterways.  Introductions should be done very circumspectly.

Karrie Reid
Folsom Foothill Gardener
Zone 9
Graduate Group in Horticulture and Agronomy
UC Davis

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I've just finished a graduate seminar on invasive plants, and there are
multiple factors involved in the process, none exclusively responsible for
success.  A few have already been mentioned and include things such as high
numbers of seed set, effective methods of seed dispersal, long-lived seed in
the seed-bank, aggressive growth habit, ability to multiply vegetatively,
ability to colonize disturbed habitats quickly.  Sometimes allelopathy is
involved, and of course, there is the absence of natural checks such as its
own native parasites and/or predators.  In addition, the invaded area may
have milder weather that allows the invader to live longer and produce more
offspring than in its native habitat.  If a waterway is involved, the issue
is complicated by the constant source of water and the ability to disperse
seeds long distances.  Very aggressive growers can displace more modest
natives.  A very interesting topic that has arisen is the idea that woody
species can take decades of establishment as ornamentals or isolated "weeds"
before becoming a truly invasive plant.  Only recently, figs have been
classified as invasive along some California waterways, though they have
been grown here since the time of the first missionaries. 
The kind of adaptation to environment alluded to in the article mentioned in
the previous email can hardly be termed evolution, as "ecotypes", or plants
of the same species more adapted to local conditions, have been known for a
long time.  This is really adaptation rather than evolution, as the species
hasn't yet changed.  I wonder how MUCH genetic variation there was between
their specimens.

The lesson we learn from invasives is to be extremely careful any time you
plant something very far outside its native home, especially if you are near
waterways.  Introductions should be done very circumspectly.

Karrie Reid
Folsom Foothill Gardener
Zone 9
Graduate Group in Horticulture and Agronomy
UC Davis
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