Communities form the biotic parts of ecosystems. The variety of species in an ecosystem is a function of its structural and functional characteristics and the diversity of its ecological processes, and the physical environment. It is from these large, regional landscapes, such as the Southern Appalachian Highlands, Sierra Nevada, and Northern Continental Divide, that people must derive sustainable yields of resources while perpetuating multiple intact examples of biologically diverse ecosystems. This hierarchy of the parts and processes of biological diversity is admittedly artificial, and it has a distinct human context. However, it provides a focus for a concept that is infinitely varied and dynamic and that must be addressed in light of the full spectrum of human needs and aspirations.
Genetic diversity refers to the variation of genes within species.
Species diversity refers to the variety of species within a region. Such diversity can be measured in many ways, and scientists have not settled on a single best method. Ecosystem components are the inhabiting species in all their variety and richness. But there is much more to consider. An ecosystem dominated by old, tall trees has a different structure than one comprised of short, quaking aspen.