Site index Introduction Trees have been called the structural elements of the ecosystem. They form the most noticeable living objects except in the driest and coldest climates.
Trees have whole communities of other organisms associated with each type.
Some birds or insects are found only in broad-leaved trees, others in conifers. In addition, trees form levels in which these communities of other animals are found. Blackburnian Warblers are found at the tops of trees, Canada Warblers lower down. Nuthatches, Brown Creepers, and Woodpeckers are typically found on the trunks and larger branches. Other definitions are used, but they are similar.