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.