Rainforest

Rainforests are complex ecosystems defined by a continuous, closed tree canopy and high humidity. They are characterized by moisture-dependent vegetation and the presence of epiphytes and lianas. A key feature of these forests is the absence of wildfire. Because they support such massive amounts of life, they are incredibly important to the planet. Estimates suggest that between 40% and 75% of all biotic species are indigenous to these forests.

The structure of a tropical rainforest is organized into distinct vertical layers. Each layer provides a unique habitat for different plants and animals. The highest level is the emergent layer. This layer contains a small number of very large trees called emergents. These trees reach heights of 45 to 55 meters, though some grow as tall as 70 to 80 meters. Because they sit above the rest of the forest, they must withstand hot temperatures and strong winds. Eagles, butterflies, bats, and certain monkeys inhabit this high zone.

Below the emergents is the canopy layer, which forms a continuous cover of foliage. This layer contains the majority of the largest trees, which are typically 30 meters tall. The canopy is a center of massive biodiversity. It is estimated to be home to 50 percent of all plant species. A quarter of all insect species also live here. Epiphytic plants, which grow on other plants, attach to trunks and branches to get water and minerals from rain and debris. Exploring this layer is difficult. Scientists use a field called dendronautics to study it. They use methods like airships, balloons, cranes, or even crossbows to fire ropes into the trees.

The next level down is the understory, also called the shrub layer. This area lies between the canopy and the forest floor. Only about 5% of the sunlight hitting the canopy reaches this level. Because it is darker, the leaves of plants here are often much larger. This layer is home to birds, snakes, and lizards. Large predators like jaguars, boa constrictors, and leopards also live here. Many seedlings that will eventually grow into canopy trees begin their lives in the understory.

The bottom-most level is the forest floor. This layer receives only 2% of the sunlight from above. Because of this low light, only specific plants adapted to darkness can grow here. Away from riverbanks or clearings, the floor is often relatively clear of vegetation. The floor is covered in decaying plant and animal matter. In the warm, humid conditions, this matter disappears quickly due to rapid decay. Many types of fungi live here to help break down this organic waste.

Rainforests are generally classified into two main types: tropical and temperate. Tropical rainforests are found near the equator, typically within 10 degrees north or south of it. They have a warm, wet climate with no substantial dry season. These forests exist in places like Southeast Asia, Sub-Saharan Africa, and South America.

Temperate rainforests occur in cooler regions. These are found in parts of North America, Europe, East Asia, and South America.

There are also other types, such as dry rainforests. These have more open canopies and occur in areas with less rainfall.

Despite the lush greenery, the soil in tropical rainforests is often quite poor. High volumes of rain wash nutrients out of the soil very quickly. The soil is also highly acidic, which makes it hard for roots to absorb nutrients. Because nutrients are scarce deep down, most trees keep their roots near the surface to catch minerals from decomposing leaves. If these trees are cleared, the exposed soil can suffer from erosion, leading to flooding. Rainforests are vital to humans; they are called the "world's largest pharmacy" because over one quarter of natural medicines are discovered there. However, they are disappearing rapidly due to deforestation and pollution.