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|Vol. 8(5), pp. 12-13||The McAllen International Orchid Society Journal||May 2007|
Tropical Nature: Life and Death in the Rain Forests of Central and South America. Adrian Forsyth and Ken Miyata. New York: Touchstone, 1995. (first published 1984). 248 pp. $14.00. ISBN 0-684-18710-8.
Fig. 1. Cover, Tropical Nature
Among orchid fanciers, the symbiotic relationship between orchids and mycorrhizal fungi is well known. Since orchid seeds are nearly nutrition-less, they require an external source of nutrients for successful germination and growth. Under natural conditions, it is the mycorrhizal fungi that provide the resources needed for a developing orchid to grow into a mature, self-sustaining plant. If there are no fungi present, the unlucky seed that begins to germinate will quickly exhaust its meager resources and die. What is perhaps less well known in this group is the general role played by mycorrhizal fungi in tropical rain forests. As Forsyth and Miyata write:
"The rain forest floor has litter, but it is often a thin layer, rarely more than a few centimeters deep. If you brush it aside with your boot, an intricately interwoven mass of white threads will be revealed just under the surface. This pallid, tangled mass consists of the rootlets of forest trees and strands of fungal mycelia. And if you carefully trace the wandering path of a fungal thread from a rotting fruit or a decomposing leaf, you will often find that it leads to the tiny rootlet of a large tree. The root systems of the massive forest giants are bound together with lowly fungi in complex, mutually beneficial relationships. These relationships, known as mycorrhizal associations, seem to operate in much the same manner as do lichens, a familiar temperate zone symbiosis between fungi and photosynthetic algae. Each member of the association specializes in the production and uptake of different nutrients: the photosynthetic trees provide important sources of energy and the nonphotosynthetic fungi provide certain minerals." (p. 18)
To a person from temperate climes whose only familiarity with the tropics is a potted orchid, mycorrhizal associations may seem to be a strange and rare characteristic of an exotic plant. However, the authors of Tropical Nature reveal it to be a common feature of many tropical rain forest plants, a feature that helps ensure that scarce nutrients remain in that ecosystem and do not wash away in the frequent rains.
Throughout their book, Forsyth and Miyata play with the contrast between temperate expectations and the usually different reality of the tropics. It is here that the authors are at their best. Attentive readers who are mostly familiar with temperate ecologies, will find that each chapter makes them cast aside their preconceptions of how nature works. For instance, a northern reader of the chapter on migratory birds may find the familiar notion that "birds fly south for the winter" being replaced with the idea that "birds fly north for the summer." If the authors are correct, this is not simply a matter of geographic perspective. In another chapter, the authors remind us that the tropics are not the rich, extremely fertile areas imagined by European explorers. Unlike temperate areas where unused nutrients are simply waiting to be claimed by enterprising farmers, in the tropics all available nutrients are locked up in the forest. Practices like slash-and-burn agriculture that release nutrients for a farmer's plants also release them to be easily washed away.
Even readers primarily interested in tropical orchids will find much material to enjoy, and not just general tropical concepts. While reading the chapter titled "Listen to the Flowers" (pp. 65-75), orchidists who never made it through Darwin's The Various Contrivances By Which Orchids Are Fertilized By Insects may well find themselves wondering at the under-handed ways some orchids trick insects into pollinating them. Those who notice the brief passage on Crassulacean acid metabolism (pp. 42-3) may question if they are controlling the humidity of their plants at the right time of day. After reading this book, orchid lovers should have a more complex view of the objects of their attentions. Orchids should no longer merely be beautiful flowers, and for orchidists interested in conservation it should be impossible to think of preserving individual species or genera without also considering the vast, complex fabric of tropical nature that created and sustains these plants.
Tropical Nature is well worth the read for anyone interested in any aspect of the tropics, whether it is the tropics in general or some specific, apparently mysterious, denizen of the tropics. Just be prepared to have some cherished notions over-turned and, if you are a bit squeamish, to have your temperate stomach churn a time or two when you read about the botfly and some of the less savory inhabitants of the tropics.