With the recent holiday season
mistletoe was everywhere. I ended up with a couple pieces that had
been gathered here locally. Now as most of us know mistletoe is a
parasite. Of course what most of us know is usually incomplete.
Mistletoe is actually only a hemi-parasite. You'll notice that it is
green. After all that's typically when we see it, in the fall and
winter as a big patch of green in an otherwise denuded tree. And
green plants perform photosynthesis. So mistletoe is producing some
of its own food. So it isn't a complete parasite.
But it does parasitize its host for
water and some nutrients. And especially in dry areas can cause
significant damage to it's host. Though most naturalists will point
out that for a healthy plant a little mistletoe is not a significant
risk to the plant's health. And there might be some that will claim
that large amounts a mistletoe is a symptom rather than the cause of
a plant's poor health.
However our view of mistletoe's role
in the ecosystem is beginning to change. Back in 2001 Australian
scientist, David M. Watson, reported on an experiment he performed.
For a patch of forest he took all the mistletoe out. Which was a
fairly monumental task. It took many months and they removed tons of
mistletoe, then went back the next year and removed a bit more.
And the result? Well individual trees
might have done a bit better, but the health of the forest, at least
in terms of biodiversity went down. Over a third of the bird species
previously found there were gone. Now perhaps you might suggest, this
was due to birds that ate mistletoe berries being unable to find food
and had left. There are birds that are significant eaters of
mistletoe, like our own desert phainopepla. But that wasn't the case.
The bird species that were missing were often insect eaters.
His paper reported that mistletoe, not
having to do much in the way of conserving its resources, since it
was stealing the resources of the larger tree. Was rather free with
dropping its leaves which left generous amounts of highly nutritious
material on the forest floor. Which would decay and provide food for
insects, which in turn fed the birds. So removal of all the mistletoe
in an area had a significant impact on the number of different
species that the forest could support.
This is an example of what in ecology
they call a keystone species. A keystone as you may, or may
not know, is the stone at the top of the arch that locks the whole
arch together. And a keystone species is similar. There may not be
many of them, but they have a large influence on the biodiversity of
an ecosystem.
For example, in 1966, the idea was
first put forward when an ecologist, Robert Paine, noted that when
starfish were removed from an area the mussels quickly push almost
all other species out of the area. Biodiversity is gone.
While many keystone species are
predators (starfish are ferocious predators), not all are. In some
areas the prairie dog is a keystone species due to their extensive
tunnel system having an impact on the environment by providing
habitat for other creatures.
We are always modifying our
environment we can't help that. But we shouldn't treat it like a game
of Jenga® where we go
about removing whole blocks and hoping that the whole structure
doesn't come tumbling down. So to have the world that we want, we
might have to have a few things in it that we don't really like. Our
forest might be a bit better off with some mistletoe in it.
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