ABSTRACT
The expression of biological diversity is fundamentally based on the genetic composition
of animal, plant, and microbial populations; hence, genetic diversity should logically be the starting point in understanding the dimensions of the issues of biological diversity. For reasons of convenience and scientific investigation, considerations of diversity can be analyzed by recognizing three of its components. Composition diversity includes the commonly recognized populations and species and the ecosystems of which they are a part. Structural diversity pertains to the spatial arrangement of physical units. For example,
structural diversity of trees at the stand level can be characterized by the number of vertical strata within the forest (e.g., overstory canopy, subcanopy, shrubs, herbaceous plants). At the landscape level, the distribution of age classes in a forest or the spatial arrangement of different ecosystems provides a measurement of structural diversity. The third component, functional diversity, represents variation in ecological processes such as nutrient cycling or energy flow. The processes driving the latter component are the most difficult to measure and understand and require long-term ecological studies. Other aspects of biodiversity are discussed in Chapter 25.
