At left: An open space caused by a blow-down of trees in the Hoh Rain Forest, Washington. Photo: Ed Shay

Three Levels of Biodiversity
In his book Ancient Forests of the Pacific Northwest, Elliott Norse identifies three levels of biological diversity.

1) There is species diversity, the kind that we are most familiar with. It is represented by the incredible variety of different species on the planet,

2) Within any species, there is genetic diversity. This is the variety of combinations possible at the molecular level and is represented by all the possibilities in the coding of the very complex DNA molecule. That gives rise to all the variations in colors or size or all the other slight differences that make individuals within the particular species,

3) The third level of biodiversity is ecosystem diversity. An ecosystem is the result of all the biological, climatic, geological and chemical "ingredients" in a particular area. This total combination of factors gives rise to certain kinds of plant and animal communities whose needs can be met by interacting with all the other parts of the system. (Norse, 1990). "Granted with permission from Ancient Forests of the Pacific Northwest, E.A. Norse, © The Wilderness Society, 1990. Published by Island Press, Washington, DC and Covelo, CA. For more information, contact Island Press directly at 1-800-828-1302, info@islandpress.org (E-mail), or www.islandpress.org (website)."

At right: Ferns growing on mosses growing on a tree in the Olympic National Forest are an example of a two-layer epiphyte, meaning a plant growing on another but deriving its moisture and nutrients from the rain and air. Photo: Ed Shay

The ecosystem of all forests is a complex web of interconnected living and dead organisms. In the temperate regions, the web tends to have high variation over space yet low density of variation of species within the same area, a condition called beta diversity by ecologists; alpha diversity consists of high-density variation within the same area and little change over space, a condition typical of tropical forests. Variation from region to region of a temperate forest may be a consequence of diverse historical conditions, such as fire, insect infestations, or other natural changes, together with soil and altitude conditions. Marchak, M. P. (1995). Logging the globe. Montreal & Kingston, Jamaica: McGill-Queen's University Press, p. 28.

[ Diversity: Ecosystem Diversity / Coastal Rainforest /
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