Ecology: Defoliating Viet Nam

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ECOLOGY Defliating Viet Nam U.S. forces are fighting not only Communist troops in Viet Nam but also the vegetation that conceals and feeds them. In thousands of sorties be tween January and September of 1967, U.S. planes sprayed 50 million Ibs. of herbicides* on 1,000,000 acres of foliage and crops in South Viet Nam. The figures this year will be even higher. To what extent is this likely to damage the country's ecology?

In response to angry criticism by home-front scientists, the Pentagon last week released a detailed study of the use and effects of herbicides. Although the report was preliminary and limited, its conclusions were clear: so far, there is no evidence that there will be long-range damage to plant or animal life in South Viet Nam.

The study was undertaken for the Defense Department by the Midwest Research Institute, a nonprofit Kansas City research organization with agricultural experience. Between August and December, MRI scientists culled 1,500 scientific articles, studied scientific and press reports from Viet Nam, and interviewed more than 140 U.S. ecologists and herbicide experts, but were not authorized to conduct on-the-spot investigations in Viet Nam. Sensitive to possible charges that MRI is biased (it has many lucrative Government contracts), the Pentagon asked the National Academy of Sciences for an evaluation of the report before releasing it. The Academy called the report "creditable," but also pointed out that definitive conclusions will require more research and data.

Killing the Kouprey? There is no question in the minds of MRI scientists that chemical defoliation works in Viet

Nam. Used along highways, canals and railroads, it kills vegetation that hides ambushers. Sprayed over forests, the chemicals cause from 40% to 75% defoliation within a month, exposing enemy strongholds and troop movements. And yet, say the scientists, the herbicides used in Viet Nam do not persist in the soil at toxic levels; new vegetation soon springs up.

Unlike insecticides, the study finds, the defoliant herbicides do not concentrate in animal tissue. As a result, dangerous effects on animals and humans are "unlikely." But temporary defoliation over widespread areas could threaten the existence of some animal species that depend on foliage for food and concealment and are already close to extinction. One of these is the douc langur, a colorful monkey that lives almost entirely on leaves. Also endangered are the Indo-Chinese gibbon and the rare kouprey, a remnant of a mid-Miocene ancestor of modern cattle.

Complete defoliation could also cause laterization, the destructive process that occurs in some tropical soils when removal of vegetation exposes them to erosion and sunlight. In South America, lateritic soil has baked into rock-like hardness and become useless with in five years after it was cleared for farming. As yet, there is no evidence of laterizing of similar soils in Viet Nam after defoliation, probably because the ground cover is never completely destroyed and grass and weeds reappear.