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Re: the more diversity the better?
There are a few different kinds of diversity. Actually, the kind of
diversity which is bandied about the most these days is actually "species
richness" and is "the presence of more species", regardless of whether
the actual number of individuals in a system are mostly of one species.
For example, a stand of Ponderosa pine may have several species of plant
in it, but most of them are Ponderosas. Then there is what is usually
meant by "diversity" in ecological terminology, which is that there are a
number of species, with no clear dominance, like a mixed hardwood forest,
for example.
Then comes the question of diversity over what area. It used to be enough
to enumerate species in a particular area and judge diversity according
to how many species were represented. From this it was concluded that
disturbed areas, or "edge effects" promoted "biodiversity" so cuts into
forests were made and tree harvesting promoted to promote "diversity".
But this "biodiversity" just reflects the number of organisms which have
adapted to taking advantage of disturbed environments. This number in
itself has become artificially high because modern agriculture has tended
to spread those disturbance favored organisms called "weeds".
Now people are starting to look at more than just numbers.You could
increase the gross"biodiversity" of a piece of land in a redwood forest,
for example, by cutting, but you would also get a lot of species that
grow in any disturbed area, and you would have eliminated the species
which survive only in intact redwood forests. To preserve global
biodiversity, you would need to allow disturbance (the inevitability of
disturbance in natural systems is another lecture) but also preserve the
less "species rich and diverse" stable ecosystems, which harbor a
different set of species.
The point I am trying to make is that "biodiversity" is a bit of a catch
phrase which has been given an absolute value, and is applied too
generally. A monocrop system is not analagous to a redwood forest. A
field is like a maximally disturbed environment, and expecting one or
even two crops to be able to monopolize it when Nature has a phalanx of
aggressive species waiting to enter is not very scientific. This is one
of the reasons that three sisters works. The squash and beans help
suppress the weeds that might otherwise over whelm the corn.
--
Karen Stark
ks36@cornell.edu
"Steal a little and they put you in jail,
Steal a lot and they make you King."
Bob Dylan
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