Many of today’s gardeners prefer to plant species native to their location in their yards and gardens. Nurseries and garden magazines alike tout the natural superiority of native plants to exotic imports, whether it concerns drought and pest resistance, or whether it revolves around the aesthetic philosophy of creating the most “natural” look possible on a cultivated patch of ground. Gardeners are also cautioned against the dangers of planting invasive exotics, such as the infamous kudzu or notorious water hyacinth.
Mark Davis has co-authored an article in Nature that challenges this current orthodoxy. As the Boston Globe summarizes the argument, imported plants (and even animals) should be judged by their performance in the local ecosystem, rather than by some arbitrary criterion of arrival date to the location.
Davis, et al, correctly point out that species migrate and go extinct even without the influence of man, so that to gauge the original status of a local ecosystem by what was observed and recorded when historicizing humans arrived on the scene is to use a false standard of measurement. Instead they urge scientists to examine how the new plants interact within the ecosystem as a whole before deciding to root out the presence of an exotic.
This more cautious approach is perhaps similar to the development of the current practice of wildfire management on public lands. Early in the US National Park system’s history, wildfires were viewed as unequivocal disasters, and every effort was made to prevent them from occurring. When a blaze did spring up, the Park Service fought it aggressively. Today, environmental scientists know that much of the Great Plains prairie ecosystem was the result of managed burns by the American Indians, who took advantage of local fires started by spring thunderstorms to clear out sapling growth and maintain the grasslands needed by the vast herds of buffalo, antelope and elk. Park Service policy is now to allow natural fires to burn within park boundaries, while maintaining enough control to keep them from reaching private lands.
While Davis and his co-authors seem to have been careful to describe their observations in fairly neutral terms, other recent writers on the topic have not been so circumspect. Hugh Raffles of the New School for Social Research compared the antagonism to introduced species to that suffered by human immigrants. Michael Pollan, the food and gardening writer, has even used the term “xenophobia” to describe the fashion for native planting among gardeners.
The new hypothesis has provoked a powerful response from other environmental scientists and botanists. University of Tennessee-Knoxville biologist Daniel Simberloff and 140 others published an impassioned critique of the article in the Letters to the Editor department of the following issue of Nature. And of course, the history of conservation biology is littered with examples of invasive species taking over a local environment when released from the control mechanisms found in predators and diseases of their former homeland.
As the Boston Globe points out, this academic battle is so acrid because it is a war over the rhetoric describing the way species grow and interact, rather than the actual mechanisms of species change in the environment. He who controls the terms wins the war of words.