|By Maryann Whitman
Cup-Plant Runneth Over
The notion of invasiveness in native plants
is one that is
distasteful to contemplate. Usually we prefer to say
that a native
plant is a “strong spreader” or an “aggressive
spreader.” At some point
it may be necessary to stop splitting hairs. I’m
of cup-plant (Silphium perfoliatum). It first
caught my attention
when it appeared in a news item as having spread aggressively
along a riparian stretch in upper New York state, where
it is not native. It had been introduced by a landowner
galloped on from there. It is now “potentially
invasive” and banned in Connecticut.
In my own
yard in southeastern Michigan I introduced it as
seed some years ago, oblivious of the fact
that it is not native to my own county.
It is spreading quite aggressively.
Fortunately it grows quite large, is hard to miss,
and therefore easy to chop down.
This is a clear example
of a native plant that behaves well in
its traditional plant community, in its
traditional habitat only to become a pest
when moved by humans into areas that it might
not have moved into on its own.
No-Till, No Problem
A brief article was published
recently in the Journal
of Environmental Quality relating no-till
farming practices and increased emissions
of greenhouse gases – most
notably nitrous oxide. Since natural landscaping
also employs essentially no-till methods
it may be a short, though erroneous, leap
in logic, in some minds, to connect natural landscaping
and increased emissions of greenhouse gases.
important to know the rest of the story:
The problem of greenhouse gases arises when fertilizers
are spread on top of last year’s
crop residue of corn stalks or soy straw,
landing several inches above the mineral
soil. When the fertilizer is injected several
inches below the surface of the soil, greenhouse
gas emissions are no longer a problem.
natural landscaping does not use fertilizers
in any case, it is safe to conclude that
gardening methods using minimal soil disturbance
will not result in the increased emissions
of greenhouse gases.
It’s All One Piece
In the early 1990s deformed
frogs with oddly shaped, missing, and extra
limbs were discovered in a pond in Minnesota.
To date, 40 states have reported similar
discoveries, and speculation runs rife
as to any causal relationships – exposure
to pesticides like Atrazine; exposure to
ultraviolet light from the thinning ozone. Pieter
Johnson, a researcher at the University of Wisconsin,
says his theory is supported by the most
solid evidence so far. He says that all
the frogs with deformed limbs that he has studied
were infected by flatworm parasites, called trematodes.
He believes that agricultural and residential
fertilizers are contributing to the parasite’s
The relationship is not by any means
a direct one. The parasite’s life cycle
involves birds, in which it releases its
eggs, that end up in bird droppings, some
of which fall in pond water and hatch; pond snails,
which are the primary host of the parasite
through maturity; and finally frogs, into whose
joints the adult parasites burrow, interfering
with limb development. Birds eat the frogs
and the cycle is repeated.
Johnson believes that
human land-use practices have contributed
to the increased populations of trematodes. “With
this trematode parasite in frogs, what we’ve
been finding is that nutrient pollution or eutrification,
basically elevated levels of nitrogen and phosphorus
in aquatic systems, can have a really strong promoting
effect on the parasite.”
Here is the rest of
the relationship that follows from what Johnson
has found evidence for: eutrophication
promotes the aquatic plant growth that
feeds increasing numbers of pond snails. Eutrophication
also decreases the percentage of dissolved
oxygen in the water. The primary predator of
the snail is the crayfish; crayfish require high
percentages of dissolved oxygen in their habitat.
there it is – all odds in this complicated
tale are stacked in favor of the parasite. And
by the way, while many states have banned the use
of phosphorus in lawn products, it is still widely
used in agricultural fertilizers and some dishwasher
soaps. Phosphorus does not break down easily in
soils – it can persist
from 20 to 100 years.
Maryann is Editor of the Wild Ones Journal, and comes to the position with an extensive background in environmental matters of all kinds.
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