Ecological Diversity
Everyone seems to agree that diversity is a good thing to have in an ecosystem. Diversity helps mitigate the effects of disturbance on a population. However, there is very little understanding about all the types of diversity. In a forest ecosystem, there are three types of diversity at work: Compositional, Structural, and Functional.
- Compositional diversity refers to the fundamental elements of diversity: the species, as well as the genetic diversity that makes up the species, plus the communities and ecosystems that provide their context.
- Structural diversity refers to how the fundamental elements of diversity are arranged relative to one another in time and space. Thus, structural diversity includes the size, shape, and distribution of species, habitats, and communities across the landscape plus patterns of change. Habitat fragmentation is a disturbance that might compromise structural diversity. On the other hand in areas where most of the forest land is in private ownership, it is the different management objectives of the owners that can create structural diversity across the landscape. There is little argument that structural diversity is critically important to biological diversity, or that a diverse landscape is important to overall forest health. Spotted owls like structurally diverse forests with everything from "old growth" to open land.
- Functional diversity refers to the diversity of ecological processes that maintain and are dependent on the other components of diversity. Functional diversity includes the many ecological interactions among species (e.g. competition, predation, parasitism, mutualism, etc.), as well as ecological processes such as nutrient retention and recycling. Functional diversity also includes the varying tempos and intensities of natural disturbances (e.g. fire) that many species and communities require if they are to persist. Because functional diversity is less tangible than either compositional or structural diversity, it is often ignored in discussions on biological diversity. However, the ecological processes represented by functional diversity provide the "ecological services" to support all organisms, including humans.
If simplicity was the old model in forest management, the new model is complexity. The pressure is on for forest managers to create and maintain complexity across large landscapes. This requires consideration of the many elements of an ecosystem. Forest management prescriptions can have repercussions on wildlife habitat, hydrological cycles, or wildfire threats to humans. Foresters must also look out over large timescales - most trees take several decades to grow and mature - in order properly benefit the forest and the resources it represent.
Cultural diversity is another important element worthy of discussion, because it is we humans who will decide the sustainability of all life forms, including our own, on earth. Biodiversity cannot adequately account for the phenomenon of our species (Homo Sapiens). With our arrival a new type of complexity and diversity was introduced. We released organic change from its age-old dependence on genetic recombination, and harnessed it to new energies: culture, symbolic language, and imagination. We can never exclude what is human from the sum of biodiversity. The Apollo landings were an astonishing breakthrough both in scientific and biological terms.
A paradox of human existence is that we live in nature and culture (society) simultaneously. Now that the works of humans have reached global proportions and much of the natural world is subject to cultural forces, it is all the more important that we do not obscure the derivative relationship between culture and nature. By accepting human intervention as a natural act, indeed as an inescapable act, we the gardeners discover the limits of cultivation.
Learn more about Ecological Diversity in our Eco-Link Sustainable Forestry or Forest Landscapes
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