TYPES OF RAINFORESTS

Tropical Rainforests

Rainforests exist across the world, not only in the tropics but also in temperate regions such as Canada, the United States, and parts of Eurasia. Like tropical rainforests, temperate rainforests receive high levels of rainfall year-round and support rich biodiversity beneath a dense canopy. However, they lack the consistent warmth and intense sunlight of their tropical counterparts. This section focuses specifically on tropical rainforests.

Tropical rainforests transition into other types of forests depending on factors such as altitude, latitude, soil composition, flooding patterns, and climate conditions. This complex mosaic of ecosystems contributes to the extraordinary biodiversity of the tropics.

Equatorial Evergreen Rainforest vs. Moist Forest

Tropical wet forests fall into two primary categories: equatorial evergreen rainforests and moist forests, the latter including monsoon forests and montane/cloud forests.

Equatorial rainforests, often regarded as the "true rainforest," receive over 80 inches (2,000 mm) of rainfall annually, distributed relatively evenly throughout the year. These forests support the highest levels of biodiversity on Earth and feature a distinct multi-layered canopy structure. Roughly two-thirds of the world's tropical wet forests fall into this category, found primarily in lowland Amazonia, the Congo Basin, and the rainforests of Southeast Asia and Papua New Guinea. Located near the equator, these forests experience minimal seasonal variation, with nearly constant temperatures and daylight hours year-round.

Tropical moist forests, by contrast, occur farther from the equator, where rainfall and day length fluctuate seasonally. These forests receive at least 50 inches (1,270 mm) of rain per year, but unlike equatorial rainforests, they experience a pronounced dry season. During this period, many trees shed some or all of their leaves, reducing canopy cover and allowing more sunlight to reach the forest floor. This increased light fosters a denser understory, setting these forests apart from their equatorial counterparts. Moist forests can be found in regions of South America, the Caribbean, West Africa, and parts of Southeast Asia, including Thailand, Myanmar, Vietnam, and Sri Lanka.

Primary vs. Secondary Forest

In discussions of tropical rainforests, the term "primary forest" refers to old-growth forests that have remained largely undisturbed by human activity. These forests retain their original structure, with towering canopy trees creating a dense overhead cover. The limited sunlight reaching the forest floor results in sparse ground vegetation. Occasionally, when a large tree falls, a "light gap" forms, allowing sunlight to penetrate and triggering the growth of understory species. Primary forests harbor the greatest biodiversity of any forest type.

Secondary forest refers to rainforest that has been altered by natural or human disturbances, including selective logging, agriculture, or storms. These forests often feature a less complex canopy, smaller trees, and lower species diversity. With more sunlight reaching the ground, secondary forests tend to support dense, fast-growing vegetation. The term "jungle" is sometimes used to describe secondary forests with thick undergrowth, though it is also applied to certain moist forests where seasonal shifts encourage lush vegetation.

According to the Food and Agriculture Organization (FAO) of the United Nations, primary forests account for roughly a third of the world’s remaining forest cover but are rapidly declining due to deforestation and logging. The loss or degradation of primary forests is estimated to occur at a rate of millions of hectares per year. Selective logging—where a few high-value tree species are harvested from an area—can degrade forests at rates exceeding deforestation figures, as it disrupts ecosystem balance and increases vulnerability to further degradation.

The time required for secondary forests to regain the structure and biodiversity of primary forests remains uncertain. Research conducted through the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) suggests that some trees in the Central Amazon may be several hundred years old, indicating that primary forests take centuries to develop.

Lowland vs. Montane Forest

Lowland tropical rainforest refers to the majority of tropical rainforest, growing on flat lands at elevations generally less than 3,300 feet (1,000 m), though this can vary. Lowland primary forest, often consisting of more than five canopy layers, is usually taller and more diverse than montane forest. It supports a greater variety of fruiting trees, which in turn sustain more fruit-eating animals and large mammals. Lowland rainforest is more threatened than montane forest due to its accessibility, more fertile soils suitable for agriculture, and the high value of its hardwood trees for timber. In many countries, much of the original lowland primary forest has been cleared, while montane forests still persist.

Tropical montane rainforest grows at elevations above 3,300 feet. High montane forests, found between 6,600 and 10,000 feet (2,500-3,000 m), are often classified as "cloud forests" because they receive much of their moisture from mist and fog rising from the humid lowlands below. Cloud forest trees are typically shorter than those in lowland forests, leading to a less-developed canopy, but they are often covered in epiphytes such as mosses, orchids, and bromeliads that thrive in the abundant moisture.

Cloud forests are found in places such as the Andes of Ecuador, Peru, Colombia, and Venezuela; Central America (particularly Monteverde in Costa Rica); Borneo (Mount Kinabalu); and parts of Africa, including Ethiopia, Kenya, Rwanda, the Democratic Republic of the Congo, and Uganda. These forests are often green with dense mosses and home to many endemic species, as they are isolated by surrounding valleys, ridges, and cliffs. Cloud forests provide habitat for numerous hummingbirds, frogs, and specialized epiphytes. However, large mammals are relatively scarce due to the limited availability of fruiting trees.

Montane forests are particularly threatened in the Andean region of South America, where they have been extensively cleared for agriculture. Many of the continent’s endangered species are found in yungas, the regional name for tropical montane forests in the Andes, yet these ecosystems remain poorly studied.

Above 10,000 feet (3,300 m), cloud forests transition into sub-alpine and alpine ecosystems, where rainfall is lower, trees become sparse, and biodiversity declines compared to lower-elevation forests.

Other Types of Forest

Seasonal or Monsoon Forest

Monsoon forests are tropical moist or seasonal rainforests found primarily in Asia (from India and Sri Lanka to China), West and East Africa, northern Australia, and eastern Brazil. These forests experience distinct wet and dry seasons, with a pronounced cooler dry period. Compared to equatorial rainforests, monsoon forests tend to be less diverse and have smaller trees.

Monsoon forests are highly threatened, especially in West Africa, where over 90 percent of coastal rainforests and monsoon forests have been cleared for agriculture.

Igapò Forest

Igapò forest refers to rainforest that is regularly inundated during the flood season, sometimes for much of the year. These forests are best known from the Amazon Basin, where they cover approximately two percent of the total rainforest area. Igapò forests contain shorter trees due to the instability of wet, poorly drained soils. These forests are sometimes called "swamp forests" and are dominated by tree species such as Cecropia, Ceiba, and Mauritia palms (aguaje palm). Many trees here have stilt roots or buttresses for stability, and fish play a key role in seed dispersal.

Várzea Forest

Várzea forests are floodplain forests that experience seasonal flooding. Unlike swamp forests, they benefit from nutrient-rich sediment deposited by whitewater rivers, making them more suitable for agriculture. As a result, várzea forests are among the most threatened ecosystems. Even in the Amazon, where most várzea forests are found, they are rapidly disappearing due to agricultural expansion and development.

Heath Forest

Heath forests grow on well-drained, nutrient-poor sandy soils and are characterized by trees that tolerate poor, acidic conditions. These forests are more stunted than typical rainforests, allowing more light to reach the forest floor, which results in dense undergrowth. Also known as blackwater or caatinga forests, they are primarily found in the Amazon Basin (notably in the Rio Negro drainage) and parts of Southeast Asia.

Peat Forest

Peat forests occur in parts of Africa, northeastern South America, and large areas of Southeast Asia (especially Borneo and Sumatra). These swamp forests develop in areas where dead vegetation accumulates as peat. The peat retains moisture and absorbs monsoon rains, but when drained for agriculture, these forests become highly flammable. During the dry El Niño conditions of 1997-98, thousands of fires burned in Indonesia’s peatlands, proving extremely difficult to extinguish.

Terra Firme Forest

Terra firme, meaning "firm earth," refers to rainforest that is not affected by seasonal river flooding. These forests are noticeably taller and more diverse than flooded forests and contain important species such as Brazil nut trees, rubber trees, and tropical hardwoods.

Mangrove Forest

Mangrove forests grow in silt-rich, brackish water habitats worldwide, particularly along river deltas, estuaries, and coastal areas. These forests have low tree diversity but provide crucial ecosystem services. Mangrove trees have adaptations such as breathing roots (pneumatophores) that allow them to survive in oxygen-poor mud.

Many unique species inhabit mangrove ecosystems, including mudskippers, which spend more time on land than in water, and Anableps, the "four-eyed fish" that can see both above and below the waterline.

Mangrove forests are among the most threatened ecosystems due to coastal development, agriculture, and aquaculture. Studies indicate that 20 percent of the world’s mangroves have disappeared since 1980. Shrimp farming is a major cause of deforestation, especially in Southeast Asia. The loss of mangroves has severe consequences for coastal fisheries, storm protection, and erosion control.