Any growth of vegetation that casts shade upon growths beneath it is a form of vegetation canopy. Such canopies form an integral part of the ecology of the area under consideration and are studied for the role they play and their effects on the local biological community as a whole. The most noted canopies are those of the large rain forests of the world, which may rise to an average height of about 50 m (165 ft) above the forest floor. These forests are likely to have secondary and even tertiary canopies formed by more shade-tolerant trees and smaller growths. Life forms, both animal and vegetable, that dwell within such canopy layers tend to be well defined for a given region, and each layer has its characteristic climate (or microclimate) conditions. Systems of forest canopies play dynamic roles in the global carbon cycle. Modeling of such processes as photosynthesis, evapotranspiration, and energy transfer for a region must therefore take canopy functions into major account. Some scientists estimate that the Amazonian canopy alone may house half of the world's species, including fully a third of the species of birds.

Bibliography: Lasky, Kathryn, The Most Beautiful Roof in the World (1997); Lowman, Margaret, and Nadkarni, Nalini, eds., Forest Canopies (1995); Moffett, Mark, The High Frontier: Exploring the Tropical Rainforest Canopy (1993).