Friday, September 25, 2009
I am a purist when it comes to thinking about habitats for plants and animals. I want it to be the way it used to be. I wish I could go back and see North America 500 years ago. I wish I could live another 300 years to see what the forest around my house will become. But there are many factors that cause a natural habitat to deviate from what it could be, or to be different from what it once was. In most of the world, we cut down whatever was there originally and planted food crops, built houses, or just abandoned the land after we harvested the original inhabitants.
I guess we are pretty lucky in the northeastern U.S., from a naturalist’s perspective. After the massive clearing of those fantastic deciduous forests, humans attempted agriculture and most of it failed economically. That process has allowed that vast area to regrow itself over the past six or seven decades in a process known as secondary plant succession. For example, the hill on which I live was a cattle pasture until 1960, so I now own a forest that is about 50 years old. This old pasture is developing as a forest mostly on its own. The trees are getting bigger and older, they flower and produce seeds, new seedlings appear and grow, develop into saplings, and so on.
So why am I on edge all the time about the biological process I am witnessing every day around me? For starters, we have a major mammalian herbivore living here—white-tailed deer. Deer eat many of these tree species, as well as various non-woody plants, and deer, therefore, influence the species composition and relative abundance of tree species in the future forest. In my forest, they seem to prefer maple, oak, magnolia, and tuliptree, and avoid ash, cherry, aspen, juneberry, and hornbeam. Given that deer densities in this region may be about 10 times their original density, they can have a significant impact on what our future forests become. Realize that I love deer; after all, I conducted my Ph.D. dissertation on Columbian white-tailed deer in the Pacific Northwest. But they have become the bane of my existence as a conservation biologist in upstate New York.
Second, there seems to be a new tree disease in the region every time I ask an expert. Chestnut blight decimated American chestnuts decades ago, Dutch elm disease pummeled American elms, and beech bark disease infected American beech; more recently we have to worry about the woolly adelgid on hemlocks and the emerald ash borer in ash trees. All of these have the potential to significantly reduce populations of these tree species and every tree disease listed above has something else in common—none of them are native to North America. The pathogens all got to this country from Europe or Asia. Introduction of non-native or exotic organisms is a major problem for the conservation of biodiversity globally (one of the so-called “Four Horsemen of the Environmental Apocalypse”).
And finally, there is the “invasion” of non-native shrubs in the forests of the U.S. In my area, the offenders are usually Tartarian honeysuckle and multiflora rose. I have both of them in abundance in my woods, or at least I did until I declared war a few years ago. I have spent many hours walking and pulling, or walking and clipping, or even walking and spraying the tough ones with the herbicide “Roundup.” And with the elimination of every individual comes that feeling of satisfaction that I am putting the system on the right track. We may not know all the species that were in this habitat centuries ago, and we may not know the relative abundances of the various native species back then, but we know that Tartarian honeysuckle and multiflora rose were not part of it.
Now that I am retired, I continue to patrol for deer with my Labrador retriever, pull up exotic shrubs, and monitor my trees for any mysterious death. I’d have to live until 2309 to see if I made any difference at all. And most of the time, I feel I am just spitting in the ocean, because the forces of degradation are enormous and the majority of the public will never know the difference. It sure is getting lonely out there.