One of the first-hand observations I have made over the past few years is the tendency to homogenize the world’s biota, especially plants. Jacaranda trees native to Brazil are common as ornamentals in Nairobi, Norway maples native to Europe are common on the streets of eastern U.S. cities, and the bird of paradise flower native to South Africa is found in nearly every city in the tropics worldwide. The botanical situation reminds me of the proliferation of franchised fast food restaurants, where you can now find Kentucky Fried Chicken outlets in Cairo and Kampala as easily as in Louisville. The homogenization of biota and the homogenization of cultures disturb me.
I tend to bond with habitats like most people bond with their friends or their pets. I also bond with humans and dogs, so I am not totally weird. But I have a close affinity to every place where I have spent considerable time: the meadows of upstate New York, the riparian habitat along the San Pedro River in Arizona, the sagebrush community in Idaho, the rain forests of Costa Rica, and, of course, the forest around my home in Ithaca. When a real estate agent is asked to name the three most important aspects of a home’s value, they usually say “location, location, location.” Similarly, we biologists often say when asked to name the three most important elements in conservation, “habitat, habitat, habitat.”
Very simply, habitat is where an organism lives. It is comprised of the plants, animals, and microorganisms in a particular location. The species composition of a habitat is determined by many factors, but it includes the climate, the historical path leading to species’ colonization or evolution in that location, the interaction of species over time, geology, soils, and more. Each habitat on earth is absolutely unique—they each have their own physical appearance, their distinctive sounds of birds, frogs, and insects, and their complex blend of odors. I am convinced that if I were blindfolded and dropped into any habitat where I have ever spent any amount of time that I could identify where I was by simply smelling the air. The ponderosa pine forest of the Kaibab Plateau and the cloud forest of Costa Rica come to mind. The sounds would make it even easier—vermilion flycatchers along the San Pedro River, bellbirds and black-faced solitaires in Monteverde, cicadas (different species) in Ohio or Las Cruces.
Now, before my ecology friends jump all over me, I realize fully that habitats are not static. Habitats change over time. The habitats I love will not be the same a century from now. During that amount of time, some ecologists would say that the habitat has changed or matured; some would say that it has become a different habitat altogether. I am not interested in that debate. I just do not want readers to think that I think these entities are unchanging. I have watched the woodland around my house change dramatically in 30 years. Therefore, I am not arguing that we do whatever we can to prevent habitats from changing. That would be folly, and would be an unwise strategy biologically.
But I am arguing that we do what we can to allow habitats to develop along a more or less “normal” path. We can also argue for a week about what is meant by “normal” or “natural.” I am bored with that argument. Simply put, there are certain events or conditions that I define as “unacceptable”, and which I think are an impediment to following a normal path to change.
One of the unacceptables is the human-assisted invasion of a habitat by plants or animals that are native to some other part of the world. That is a no-brainer for me, and a reason I spend many hours per month eliminating Tartarian honeysuckle, multiflora rose, autumn olive, and common buckthorn from my woodland, four species indigenous to Eurasia. I know they were not here a century or so ago, so when I see them it offends my sensibilities. From a conservation perspective, I am not even sure there is a practical reason to eliminate them. Certainly, if they became superabundant, they would exclude native plants from growing there, with the result that some ecological interactions between those native plants and other organisms would be disrupted or extinguished. But when they are in limited abundance, their greatest danger may be that they will not remain at such low densities. I eliminate these plants because I can; the large Lumbricus earthworms that are so common in my part of the world are not native here either, but there is little I can do to diminish their numbers.
To me, there is a certain parallelism between what I observe in our native habitats and what I observe in cities around the world. When I am in a foreign country, the last place I want to eat a meal is in a Pizza Hut or a McDonalds (in fact, I guess they even kind of offend me here). And when I am in a forest near Ithaca, NY, the last plant I want to see growing there is a European or Asian species. In both cases, something is being lost and, although I can not put to words exactly what that loss is, I believe it is important. But it goes something like this for me: The invasion of our landscapes with non-native plants is like a technician at the Louvre deciding to "touch up" the Mona Lisa with watercolors. The average person would not even see the difference, but the art expert probably would. The act of changing the Mona Lisa, the most famous painting in the world, would transform this important and beautiful object from what it was to a different piece of art.
On the other hand, are Costa Ricans or Egyptians offended when they see an American franchise restaurant in their cities? Possibly not. They might even think it is chic that they have this international influence. I don't get offended to see a Chinese restaurant in Ithaca, but seeing a Pizza Hut in Alexandria bothered me a great deal. Maybe I am uncomfortable because I fear that these restaurants, and these invasive plants, will not simply be an addition to what was already there, but that they will come to replace the original. This creeping sameness makes the world less diverse and less interesting, but does that bother anyone else?
So I pull and cut and sometimes spray and my students think I’m that crazy ex-prof who would rather declare war on invasive plants than talk on a cell phone. How weird. And I eat rice and beans in Costa Rica instead of Big Macs, and I eat hummus in Egypt instead of pizza. Is this what happens to us as we age? We rebel at "progress"? We cuss at the automobile for replacing the horse, or lament that email caused the extinction of the hand-written letter. Or that friends were replaced with acquaintances. Or that family time was replaced with sitcoms. I wonder, maybe I just have too much time on my hands.