Tropical Rain Forests: Potential Source of New Drugs?

TROPICAL RAIN FORESTS: POTENTIAL SOURCE OF NEWDRUGS? D. D. SOEJARTO* and N. R. FARNSWORTHt It is an accepted fact that the tropical rain forests are the richest biome on earth. It is also an accepted fact that the tropical rain forests still represent one of the last and true great frontiers of wilderness, which still evoke awe and wonderment. Sadly, however, this state ofaffairs may not last long enough into the future for man to unlock all their secrets. In view of the fact that our institution is currently involved with the U. S. National Cancer Institute's recently resurrected plant program 1, and mindful of warnings from conservationists that the tropical rain forests or tropical moist forests or simply rain forests 2 may be decimated within the next decade or so, in addition to a concern brought by personal knowledge of the situation through a number ofyears of field and laboratory experience, we consider it timely to put into perspective the prospect that this tropical biome may still contribute to the alleviation of human sufferings, before it vanishes from the face of the earth. It terms of human existence, the tropical rain forests represent a store of renewable natural resources, which have for eons, by virtue of their richness in both animal and plant species, contributed a myriad of items for the survival and well-being of man. These include basic food supplies, clothing, shelter, fuel, spices, industrial raw materials, and medicine. It is to this last item, medicinal or ethical drugs, that this essay is addressed.? Associate professor, Program for Collaborative Research in the Pharmaceutical Sciences, College of Pharmacy, University of Illinois at Chicago, and Research Associate, Field Museum of Natural History, Chicago, Illinois 60605 (correspondence address). tResearch professor and director, Program for Collaborative Research in the Pharmaceutical Sciences, College of Pharmacy, University of Illinois at Chicago, 833 South Wood Street, Chicago, Illinois 60612. © 1989 by The University of Chicago. AU rights reserved. 0031-5982/89/3202-062101. 00 244 I D. D. Soejarto and N. R. Farnsworth ¦ Tropical Rain Forests Definition and Extent of the Tropical Rain Forests Following the classical definition of Schimper, later adopted by Richards 3, the tropical rain forests are defined as an evergreen plant community, at least 30 m in height, rich in great woody lianas and in arborescent and herbaceous epiphytes, but the woody forms predominate. Mature forests have a closed canopy and contain several more or less distinct strata, thus creating a habitat complexity characteristic ofthe tropical rain forests. Although other definitions, variants of the above wording, have been offered, this definition remains valid to this day and reflects the true nature of this forest ecosystem. Tropical rain forests are a climax vegetation that has developed only in the tropical belt, where the climatic conditions are characterized by constant high temperature and humidity, with abundant rains. This translates into a mean temperature of 24°C or higher and essentially frost-free, with an annual precipitation of 2, 000 mm or more, and not less than 100 mm in any month, for 2 out of 3 years 2, 4, 5. Such areas lie within the boundary of the tropic of Cancer in the north and the tropic of Capricorn in the south, normally occur below 1, 300 m above sea level, and include lowland rain forest, montane (and submontane) rain forest, cloud forest, riverine forest, swamp and bog forest, and wetter forms of lowland seasonal forest 6. Under this definition, the tropical rain forests presently cover an area of about 9 million km2, about 7 percent of the earth's land surface. Of this extension, 5. 1 million km2 are in tropical America, 1. 9— 2. 1 million in Asia (largely in Southeast Asia), and 1. 8 million in Africa, with patches in a few Indian Ocean and Pacific islands 2, 4, 7. Biotte Richness Estimates on the biotic richness of the tropical rain forests place the number of species (both animal and plants) between 3 million and 30 million 4, 5, 8, 9. The great bulk of these constitute the insects, which live in the forest canopies 9. The number of species of seed plants occurring in the tropics. . .