OPINION: Invasive plants - lovely, but an enemy
August 14, 2009 by JESSICA GUREVITCH
BY JESSICA GUREVITCHJessica Gurevitch is professor and chair of the Department of Ecology and Evolution at Stony Brook University.
There is a lovely nature preserve near where I live and work on the north shore of Suffolk County, with woods and fields, where day hikers come to breathe in the salt air and enjoy nature. Entering the preserve you soon come to a meadow - or what was a meadow, not long ago. Now it is a carpet of a single plant species - an invasive vine called porcelain berry - that blankets everything else that once lived there: full-grown trees, little saplings, shrubs, other weeds, grasses and wildflowers.
I can't say for certain what the effects of the out-of-control porcelain berry vine are on the birds, white-footed mice, turtles and bees that live there - I haven't studied the situation - but anytime you have such substantial structural change you will almost undoubtedly see many different, and complex, impacts. Perhaps some species are helped; it is likely that others are harmed.
Invasive plants such as the porcelain berry are familiar to many of us, because they are everywhere. Kudzu, notorious in the southern United States, is now becoming established here and there on Long Island, moving north as our climate inexorably warms. Hydrilla, a plant that has choked bodies of water across the south, is appearing in the northeast and has been found this summer in Lake Ronkonkoma and at lakes in Sayville and Smithtown.
Some of these plants we actually like. A large percentage were brought in and planted as ornamental or other horticultural plants. But they can do a great deal of harm and raise lots of scientific questions, many practical issues and even some philosophical ones.
We may wonder, for example, why do they keep spreading? And when we pull them out, why do they keep coming back? Is the situation ever going to be "fixed" or is it just becoming worse? Are volunteers doing the right thing by pulling out the intruders? Do their efforts really make a difference? And then, does it really matter whether plants are native or not?
Most invasive species got here in the first place because people transported them (on purpose or accidentally), and a large proportion have been propagated by people and are or once were widely planted by people. After they arrive, some are very good at protecting their self-interests.
The hydrilla, for instance, is originally from Asia and probably got here by being dumped from people's aquariums. It is spread from one lake to another by pieces attached to boats. Once in a lake, it can grow and reproduce astoundingly quickly, tolerating almost any environmental conditions you can throw at it.
Homeowners, landscapers, and various state and federal agencies have used invasive plant species as ornamentals, cattle forage and to prevent soil erosion (for example on slopes adjacent to highways), among other purposes, choosing them because they are pretty, rugged and grow vigorously. Those last two traits also help make them highly invasive and difficult to combat.
We sometimes seem to know better than to propagate them now, but the cat's out of the bag. Invasive plants keep coming back even without our help, because evolution has finely tuned these species to take advantage of conditions that humans are making so abundant - places where trees were cut down and soil dug up, leaving open sites with plenty of sunlight. These are inviting places for a seed to take root or into which an underground stem can find its way.
While some are working to develop legislation on Long Island and elsewhere to limit the sale of invaders and substitute those less damaging to our natural environment, many developers, landscapers and homeowners continue to plant highly invasive species, such as the familiar Norway maples and Japanese barberry bushes.
But it's worse than that. While one group searches for ways to limit invasive plants, others are promoting efforts, with government support, to breed and grow potentially highly invasive plants for the production of biofuels.
Ecological research scientists have recommended using alternatives that are non-invasive, but it is not clear that the message is getting through. Unfortunately, the very characteristics that make plants valuable as biofuels - fast growth, high photosynthetic rates, no known diseases or pests, rapid spread through underground rhizomes and so on - make them ideal invaders of natural habitats.
Is the situation ever going to be fixed? Invasive plants will be here for all of our lifetimes, and more so if we continue to energetically and enthusiastically spread and nurture them. But even if we stop planting them, they will do pretty well spreading on their own. The efforts of volunteers make a huge difference - the difference between choked fields and streams and those in which the native biodiversity is flourishing. Like farmers fighting agricultural weeds or parents raising teenagers, the effort seems never-ending, but neglect and capitulation are not options.
Research professors in the fields of ecology and conservation biology around the world are studying ways to predict, limit and prevent the spread of invasive plants and how to most effectively remove them, mitigate their damage, and restore ecosystems they have invaded. But nature is complex, and not all of these plants are harmful all of the time.
Scientific research on when invasive plants do the greatest damage to biodiversity is ongoing. It is clear that under some circumstances, such as the meadow in the preserve where I go walking, the effects are highly deleterious.
The plants may disrupt ecosystems and cause all manner of mischief in many natural environments we are keen to preserve. For instance, invasive grasses can dramatically increase fire frequency in some environments, killing fire-susceptible native plants.
But in other circumstances, they seem to do little damage. On islands worldwide, the invasion of non-native plants has not resulted overall in widespread extinctions of native species; rather, the average number of species has approximately doubled, as non-native and invasive plants are just added to the native biota.
We simply do not fully understand what effects invaders will have, and when they are likely to be most harmful.
But then, you might ask, what does it matter? Isn't a green plant a green plant, regardless of where it's from?
While many of us fail to notice the differences, and are unaware of the diverse natural world around us, when we open our eyes and minds and perceive those differences, we can learn to identify which plants have evolved and adapted here over eons, and which are the rapidly spreading weeds. Recognizing the differences, our own life is vastly richer, and our ability to protect and preserve our environment is far greater.