In the Preface to this book, we asked, are tropical forests more fragile than forests at higher latitudes? Are tropical forests, especially rain forests, particularly susceptible to disturbance? Is recovery following activities such as logging and shifting cultivation slower and more difficult than recovery of temperate zone forests? The answers to these questions have important implications for managing tropical forests for non-timber forest products as well as for wood. To answer these questions, we examined the literature on structure and function of tropical forest ecosystems. Results suggested that tropical forest ecosystems are different from higher latitude forests in ways that make tropical forests more fragile. The five major categories of differences are:
• high diversity of species;
• high frequency of cross-pollination;
• common occurrence of mutualisms;
• high rate of energy flow through primary producers, consumers, and decomposers;
• a relatively tight nutrient cycle.
The high diversity of species means that there are fewer individuals of any species per unit area, and thus the probability of some species becoming locally extinct following logging or other disturbances is relatively high.
The high frequency of cross-pollination means that at least two rather than one individual per species must remain per unit area to prevent losses of genetic diversity, and in some cases even local extinction.
The common occurrence of mutualisms in tropical forest ecosystems means that elimination of one species of plant or animal can result in the elimination of other species of plants or animals. For example, tropical tree species are frequently pollinated by animals that may become extinct due to large-scale disturbances.
The high rate of energy flow through moist tropical ecosystems means that decomposition is rapid, and thus there is high potential for loss of soil organic matter and nutrients. Soil organic matter is critical for the continued health of the whole forest ecosystem.
The tight nutrient cycles on or near the soil surface in moist tropical forests are more easily disrupted by logging and other activities than nutrient cycles in forests where nutrients are held more readily in the deeper mineral soil.
Because of this high susceptibility to disturbance, tropical forests must be managed with special care, if the forests are to reproduce and maintain their productivity in the long term. To ensure reproductive success, care must be taken that sufficient individuals of each species remain in close proximity, and the network of mutualisms must be left relatively intact. To ensure that sufficient organic matter remains on or in the soil, and that nutrient cycling mechanisms remain intact, the basic structure and function of the forest must be maintained.
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