Invasive Plants- its not evolution

"So why aren't people just another means of plant dispersion? Isn't the spread of non-native species just an example of an organism evolving into a new environment?" If ever there was an argument invasion ecologists would love to put to bed, it is that one. Though never reaching wide acceptance, this idea has existed in the gardening world in varying degrees of extremity for as long as the term 'invasive plant' has been known beyond the realm of theoretical ecology. Such arguments usually run along the same theme: the case against non-native plants is at best anti-humanist and at worst an expression of latent xenophobia. The argument is summed up quite nicely in "Against Nativism", a New York Times article by noted science writer Michael Pollan from 1994. It may not be quite fair to hold words written by Mr. Pollan, whose books I quite like, fourteen years ago against him (though he apparently reconfirmed his convinctions more recently in the blogosphere). But I only read the article recently, and its a good medium from which to make a few points.

I'm going to leave the philosophizing aside. Of course such conjecture about the extent to which humans should influence the natural world is a value judgement. In a broad sense, I actually agree with quite a bit of this article. There are roughly fifty thousand introduced plants in use throughout the United States. Of those, only a fraction are considered invasive, with as few as thirty marked as high conservation priority in New Jersey. Many naturalized weeds confine themselves to old lots and other waste places, such as the wild carrot to which Mr. Pollan refers. Such plants can hardly be thought of as invaders and, much like the House Sparrow, their global distribution has become part of the story of human immigration. Of course one can say, "well they still occupy a place a native plant could be", but ultimately their impact is miniscule compared to more pressing issues.

But what of the thirty that do not behave themselves? Here, Michael Pollan's argument takes a turn that took me by surprise. Here's what he had to say:

"There's no question that these migrations are sometimes destructive of the ecological status quo, if indeed such a thing even exists. But migrations of species by whatever means is an abiding part of natural history; in any event, they're almost always irreversible. Turning back the ecological clock to 1492 is a fool's errand, futile and pointless to boot. It seems to me we gardeners would do better to try to work with the mongrel ecology we've inherited -- to start out from here."

Coming from the champion of food production as a complex system, I was struck by the over simplification implied in this statement. An ecosystem is a mind-bogglingly complex thing, this we've already established. To suggest that a plant out of its ecological context, free of its natural predators, pests, and competitors, will merely be a blip in our region's natural history seems incredulous. Its like throwing a rock at a glass house and not only expecting the house to rebuild itself, but to find a useful place for the rock as well. Can we truly call this evolution? I would argue that we can't. To me, evolution is the sum of a species' trials and tribulations, the series of influences that defines its niche. In absence of this, is a species truly evolving? In a strictly biological sense of course, but in an ecological context its role becomes boundless and therefore meaningless. A different word is in order, and 'invasion' certainly describes what happens quite well.

I am also bothered by the suggestion that human transport represents merely another form of migration. I don't think it is quite that simple. While I'm sure there is a myriad of reasons one could point out as to why thats true, a big one come to mind for me. First of all, these introductions are not random. Most invasive plants were purposely selected and brought here for horticultural purposes. Given the harsh nature of formal landscape, a species' resilience is often heavily considered. I wrote more about the ecological issues associated with this idea here, so I wont go into detail. But if we accept that this "human selection" plays a role in vetting invasive species, how can such a 'migration' be akin to movement by wind or water? Mr. Pollan is right to say evolution will draw no distinction, but he fails to consider the fact that we've already taken care of this before a plant can even make it to the natural environment.

Ecology is very much a "sum of all its parts" concept. I certainly do not prescribe to the idea that humans play no role in shaping the natural world, but I am skeptical that moving plants between natural environments at distances of thousands of miles constitutes a helping hand or represents a natural process. The level of disruption is too great for me to accept that it is merely a change in status quo. Trying to frame the results of biological invasion in philosophical argument stems from a failure to recognize that we as a species are quite capable of being a negative influence on the natural world. If believing such makes me anti-humanist, than so be it.

Anyway, I'm sure there will be more on this later. For now it is a great day and I'm going back outside.