Emergent Layer
This is the widely spaced, uppermost layer, which contains the tallest trees that have broken through the forest canopy. Its height ranges from 100 to over 300 feet as in the California coastal redwoods, exposing it directly to the weather. In tropical rain forests, this sparse layer must withstand hotter and drier temperatures than the layers beneath. It is home to birds of prey and insects.
Canopy Layer
Composed of the majority of the largest trees, the canopy ranges in height from 90 to 280 feet. Tropical canopies are dense and flat-crowned, though their branches do not typically interweave or touch, which acts to deter infestations of insects and disease. Most of the tropical animal life inhabits this layer, including insects, frogs, snakes, bats, parrots and monkeys. It also contains the densest biodiversity. Temperate canopy trees consist mainly of spruce, fir, cedar and hemlock, and contain far less animal life than their tropical counterparts. The canopy filters out 70 to 80 percent of the sunlight.
Understory Layer
Constantly shaded, this layer ranges from the ground up to the canopy. Its foliage includes small trees and young canopy trees. The air is calm and humid. Epiphytes, or plants that grow on other plants, are found here in abundance. Tree trunks dominate this stratum, often playing host to epiphytic growth. A tropical understory contains no dominant species, but grows palms, vines, strangler fig, tree ferns, orchids, bromeliads and broad-leaf plants capable of photosynthesizing the scarce sunlight. A temperate understory grows mosses, ferns, nettle, berry shrubs and small shade-loving trees like dogwood or broad-leaf maple.
Forest Floor
The ground layer of a rain forest varies significantly between tropical and temperate. A tropical rain-forest floor grows few plants due to the low sunlight. It is made up largely of tree roots, fungi, soil and decaying matter. The heat and humidity promotes rapid decay by decomposers like fungi, termites and earthworms. The soil is poor, and nutrients are quickly absorbed by the shallow roots of surrounding trees. Temperate rain-forest floors are usually carpeted with thick mosses and lichens that require low light, along with ferns, grasses, wildflowers and fungi. Also present are fallen "nurse logs" from which seedlings sprout and grow. The soil is rich, but nutrients decompose much slower than a tropical rain forest. Most animals in temperate rain forests live here, some examples being elk, bear, mice and slugs. The forest floor receives less than 2 percent of available sunlight.
