Complex ecosystem in which trees are the dominant life-form.
Tree-dominated forests can occur wherever the temperatures rise
above 50 °F (10 °C) in the warmest months and the annual
precipitation is more than 8 in. (200 mm). They can develop
under various conditions within these limits, and the kind of
soil, plant, and animal life differs according to the extremes
of environmental influences. In cool, high-latitude subpolar
regions, taiga (boreal) forests are dominated by hardy conifers.
In more temperate high-latitude climates, mixed forests of both
conifers and broad-leaved deciduous trees predominate. Broad-
leaved deciduous forests develop in midlatitude climates. In
humid equatorial climates, tropical rainforests develop. There
heavy rainfall supports evergreens that have broad leaves
instead of the needle leaves of cooler evergreen forests. Having
extensive vertical layering, forests are among the most complex
ecosystems. Conifer forests have the simplest structure: a tree
layer, a shrub layer that is sp