The understory is the section of the forest close to the ground, in contrast with the canopy, the high point of the forest. In rainforests in tropical and temperate regions of the world, this section is a totally different environment, fostering unique plants and animals. This area of the forest is also of great interest to humans, since humans must travel through it if they wish to move around in the forest.
A number of traits distinguish understory plants, trees, and shrubs. All of them are capable of tolerating low light conditions, since much of the light is filtered out by the high forest canopy above. These plants also like moist, humid environments, and they tend to grow low to the ground. Seedlings of canopy trees start out in the understory, paired with shrubs, plants, and herbs. Seedlings are often repressed until a canopy tree dies off, making room for the seedling to shoot up into the forest canopy.
The ground in the understory is usually very thick, carpeted with a rich layer of leaves, flowers, animal droppings, and decomposing organic material. Many fungi make their homes there, and the leaf litter also harbors insects, grubs, and a variety of other small creatures. Animals like to nest in the understory, taking advantage of the dense plants for protection and camouflage, and numerous plants provide sources of food in the form of bright, appealing fruit, tender foliage, and habitat for food animals.
Unlike the canopy, which can be quite noisy, the understory is very quiet and still. Especially in the heat of the day, it can feel almost oppressive, with barely a breeze to stir the plants, and no animals on the move. Occasionally, calls from animals high up in the canopy can be heard, along with small rustlings of ground-based animals. This section is also humid, thanks to all the trapped moisture in the leaf litter and plants.
Understory plants tend to grow very rapidly, because they are designed to take advantage of their conditions. If a fire sweeps through this area, new plants germinate within days, and some species are actually specifically designed to germinate after fires. Plants also take advantage of temporary clearings created by dead trees, with the trunk of the dead tree decaying to add to the rich layers of soil and organic material on the forest floor while understory plants quickly sprawl across the area, often breaking the trunk down along the way.