Forests are habitats in which the trees are the dominant form of vegetation. They occur in many regions and climates around the globe—the tropical rainforests of the Amazon basin, the temperate forests of eastern North America, and the boreal forests of northern Europe are just a few examples.
The species composition of a forest is often unique to that forest, with some forests consisting of many hundreds of species of trees while others consist of just a handful of species. Forests are constantly changing and progress through a series of successional stages during which species composition changes within the forest.
Thus, making general statements about forest habitats can be difficult. Yet despite the variability of our planet's forests, there are some basic structural characteristics that many forests share—characteristics that can help us to better understand both forests and the animals and wildlife that inhabit them.
Mature forests often have several distinct vertical layers. These include:
- forest floor
- herb layer
- shrub layer
These different layers provide a mosaic of habitats and enable animals and wildlife to settle into various pockets of habitat within the overall structure of a forest.
The forest floor is often blanketed with decaying leaves, twigs, fallen trees, animal scat, moss, and other detritus. The forest floor is where recycling occurs, fungi, insects, bacteria, and earthworms are among the many organisms that break down waste materials and ready them for reuse and recycling throughout the forest system.
The herb layer of the forest is dominated by herbaceous (or soft-stemmed) plants such as grasses, ferns, wildflowers, and other ground cover. Vegetation in the herb layer often gets little light and in forests with thick canopies, shade tolerant species are predominant in the herb layer.
The shrub layer is characterized by woody vegetation that grows relatively close to the ground. Bushes and brambles grown where enough light passes through the canopy to support shrub growth.
The understory of a forest consists of immature trees and small trees that are shorter than the main canopy level of the tree. Understory trees provide shelter for a wide range of animals. When gaps form in the canopy, often times understory trees take advantage of the opening and grow to fill in the canopy.
The canopy is the layer where the crowns of most of the forest's trees meet and form a thick layer.
Emergents are trees whose crowns emerge above the rest of the canopy.