This need not be, and in most cases cannot be, a lengthy and expensive study. Much can be learned by knowledgeable scientists from a literature review, site visit, and study of topographic maps and aerial or satellite photos. On the basis of this information, an environmental impact assessment is prepared. This includes an analysis of the potential impacts of the various alternatives as well as recommendations of alternatives and mitigation measures. This information is fed back into an environmental management plan for the project siting and design process. The site and project design alternatives are selected and permits and other approvals are obtained.
During the construction phase of the project, environmental monitoring begins. Monitoring may begin before construction if additional, site-specific environmental data are needed. Monitoring to establish a baseline against which to measure future impacts is usually not feasible because of the time, scope, and cost of a study required to define natural variation. Therefore, the monitoring program must focus on environmental parameters and populations likely to be affected during the construction and operations phases of the project. Environmental impacts are assessed and the information is fed back into an environmental management plan that becomes part of the operations plan for the project. Monitoring continues to some degree during operations so that impacts can be assessed continually and the management and operations plan can be modified as necessary.
Once this process is completed, the environmental and engineering information generated becomes extremely valuable to those planning similar developments or different projects in similar habitats. Therefore, dissemination of the results—including both successes and failures—is critical.
Tropical forests are complex environments that support a greater diversity of plant and animal species than any other terrestrial habitat. Most of these species (e.g., insects) have not been named, described, or studied by scientists. Raven (1994) estimates that there are 8-10 million species on earth, though only 1.4 million have been named. Tropical forests are also rich in substances, both medicinal and industrial, that are useful to their indigenous residents as well as society at large (Lewis, 1990).
Tropical rain forests receive 80-300 inches of rainfall a year (Holdridge, 1967). They typically consist of a relatively tight canopy of broad-leafed evergreen trees and two or more underlying layers of trees and shrubs. Undergrowth vegetation is usually sparse because little sunlight reaches the forest floor. Soils are typically acidic and poor in nutrients. Nutrient cycling depends on degradation of leaf litter, fallen trees, and shrubs on the forest floor. Because this cycle is so easily altered by disturbance, tropical forests are among the world's most sensitive environments (Wilson, 1988). The largest remaining contiguous tracts