Discovering the Forests of Alaska , Oregon, and Washington

What Is an Ecosystem?

Ecosystems can be studied in terms of their structures, composition, and processes.

Structures: The different physical pieces of an ecosystem and their arrangement. In a forest, examples of structures are large, old trees; young seedlings and saplings; standing dead trees and snags; and dead trees that have fallen to the forest floor.

Composition: The individual species in an ecosystem. Each ecosystem has a group of species that are most typical. There are hundreds of tree species in the world, but only some of these species grow in Alaska, Oregon, and Washington forests. Each forest type has a group of tree species that are typically found in it. Some tree species grow only in certain ecosystems. Other species have wider ranges and are found in several or even many ecosystems. The species of animals, fungi, and plants other than trees also differ among ecosystems.

Processes: The ecological processes essential to a forest are universal in all ecosystems. Plants such as trees sprout from seeds, grow, reproduce more seeds, and eventually die. Animals are born, eat, grow, reproduce offspring, and die. Organic matter, both plant and animal, is recycled back into the ecosystem.