OBERLIN, OHIO. — Oberlin, Ohio -- A basic law of ecology is that living things are tightly dependent on one another, often in ways that are not easy to imagine.
Who, for example, would have predicted that when the last dodo was killed in 1675, that death would lead to the slow extermination of the tambalocoque tree, whose fruits germinate only after passing through the dodo's digestive system? Now no natural stands of tambalocoque younger than 300 years can be found.
Or who would have predicted that clear-cutting tropical rain- forests would so significantly alter local weather patterns that the tropical rainforest biome itself and its vast diversity of life might not survive?
Such interactions are worth noting because of the possible ramifications of a phenomenon that ecologists have just begun to document. Mushrooms worldwide appear to be in a catastrophic state of decline.
Throughout Europe, in countries with terrains as diverse as Holland, Germany, Austria, Czechoslovakia, Poland and England, wild mushrooms are becoming increasingly difficult to find. Those fungi that are found are significantly smaller than those found years ago. Preliminary data suggest that the same troubling situation is occurring throughout North America as well. The decline has been so precipitous that biologists have begun to refer to it as a mass extinction.
The two obvious explanations for the demise of the mushrooms -- habitat destruction and over-picking of edible types by an ever growing human population -- have been ruled out. Sophisticated sampling schemes designed by ecologists control for the fact that there is less land available for wild mushrooms; they have been declining at a rate that far exceeds the rate at which land is being developed. The fact that the decline has affected both edible and inedible mushrooms equally indicates that humans hunting for tasty treats are not the main cause of the problem.
The loss of wild mushrooms worldwide might not seem like that big a deal, but the consequences may well be grave because of the way those fungi interact with other life forms. If the mushrooms die off, ecologists fear that our forests may not be far behind. Many mushrooms live in close association with trees; the mushrooms provide the trees with water and minerals while the trees supply the mushrooms with carbohydrates. The mushrooms' underground filaments often extend much deeper into the soil than do the roots of trees, thus making available to trees resources that would otherwise be unusable.
Ecologists have found that trees lacking mushrooms are significantly more susceptible to environmental stress than those growing with the fungi. Eef Arnolds, an ecologist specializing in mushrooms at the Agricultural University of the Netherlands thinks that ''severe frost or drought could lead to a mass dying of trees.''
Although the cause of the decline has not been pinpointed, most experts believe that the mushrooms are responding to abnormal atmospheric levels of nitrogen, sulfur and ozone. Dr. Arnolds suggests that in Holland the main culprit appears to be excessive nitrogen applied as fertilizer to agricultural fields. Once again it appears that we are seeing the unpredicted effects of our wanton pollution of our environment.
If the experts are correct about the cause of the decrease in mushroom populations, the mushrooms can provide us with some very critical information and insight. Like the canaries that miners used to bring into mine shafts to warn of a lack of breathable air, these small indicator species are warning us about the state of our planet. We can only hope that collectively we have enough sense to begin to pay attention.
Michael Zimmerman is associate dean of the College of Arts and Sciences at Oberlin College.