Wrong Trees in Wrong Place Wreak Environmental Havoc

MICHAEL ZIMMERMAN

August 22, 1991|By MICHAEL ZIMMERMAN

Oberlin, Ohio -- We've come a long way from Ronald Reagan's pronouncement that trees are notorious polluters -- maybe too ,, far. Almost everyone in sight these days is promoting the planting of trees as a means of helping to stem the rising tide of greenhouse gases. The problem is that almost everyone, from President Bush on down through the National Arbor Day Foundation, is doing it in what must be considered an environmentally blind fashion.

In a stinging indictment of the tree planting movement, Audubon Magazine columnist Ted Williams claims that tree promoters are actually doing more harm than good. Speaking of average citizens who have been swept along by the tree planting bandwagon, Mr. Williams says, ''It's not that tree-planters don't do lots of good by frequently planting trees in the right places, and it's not that they aren't nice people who mean well. It's just that, in their innocence, they are an environmental menace.''

Their confusion falls into three major categories: Disrupting natural ecosystems by planting non-native species; destroying natural ecosystems by planting trees where, ecologically, none were meant to be; and providing the public with terribly erroneous information in the guise of ecological advice. All three problems are more significant than they might appear at first glance.

While it is surely true that trees are capable of absorbing an awful lot of the most abundant greenhouse gas, carbon dioxide, the wrong tree in the wrong place is capable of causing a large amount of environmental damage.

For the past 70 years, ecologists have known that when non-native species are introduced into new environments, typically without the predators, parasites and competitors with PTC which they co-evolved for thousands of generations, they often out-compete many of the native species and become pests.

The blue gum eucalyptus that was introduced into California from Tasmania is one such example. It has spread so well that it has overrun entire native ecosystems endangering many plants and animals. Huge numbers of the trees that are being pushed are alien to North America, with perhaps the most common being the Afghan pine.

A number of thoughtful local environmental organizations have agreed to participate with the national tree-planting groups only with the guarantee that exclusively indigenous species would be promoted. No such assurances have been forthcoming.

Even when native species are planted, some habitats are ecologically inappropriate for their introduction. The tall-grass prairie, stretching from Ohio to western Kansas, although naturally devoid of trees, is a magnificent ecosystem. Nonetheless, Julius Sterling, the founder of the National Arbor Day Foundation, started the group in 1870 to create ''a grand army of husbandmen . . . to battle against the timberless prairies.'' The organization, as if in bizarre misappropriation of Freud's famed penis-envy theory, still espouses this strange goal. Similarly, many naturally tree-less hillsides in San Francisco have been blanketed with non-native trees while the original native grassland-wildflower communities have been forever lost.

The tree planters have also set their sights on environments that typically have trees but presently do not. The problem is that too frequently these treeless areas achieved their present, naked state as a result of natural environmental occurrences, such as fires and floods. The normal sequence of events is for these disturbed environments to undergo a successionary process whereby a full complement of plants will eventually be re-established.

Rushing in with trees, either native or alien, only disrupts the natural process and makes it less likely that a stable community will be mature. And yet the American Forestry Association-sponsored Global ReLeaf organization has done just this by planting 137,500 trees in South Carolina's Francis Marion National Forest in the wake of Hurricane Hugo. Additionally, in spite of wise resistance from the National Park Service, the National Arbor Day Foundation is advertising that ''millions of trees must be planted'' to help Yellowstone recover from its 1988 fires.

The misleading message from these misguided efforts is that natural processes are incapable of creating a stable ecological balance, that only human efforts are effective at doing so.

Planting trees can be an environmentally sound thing to do. But the specific trees and the specific locations must be chosen with care, knowledge and respect. Environmental interactions are beautifully complex, and heedless tree-planting too often leads to environmental havoc.

Michael Zimmerman is professor of biology and associate dean of Oberlin College.

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