Oftentimes, when discussing ecological change and trends in global forest cover there is a tendency for writers and media to use terms such as tropical forest and rainforest interchangeably. These two forest biomes share similar characteristics, and even display some geographical overlap, however there are a handful of differences that are important to know.

The primary difference between these two biomes can be found in their names. Tropical forests are loosely bound between the Tropic of Cancer and the Tropic of Capricorn whereas rainforests are defined by their yearly precipitation and climate. Though the tropics serve as a general delineation point, ecosystems categorized as ‘tropical rainforest’ — systems that meet both definitions — form a very small percentage of all tropical forests.

Tropical Forests

Finding a singular definition can be difficult due to the nature of their ecosystems. Although the Tropics act as a simple delineation point, given an advantageous climate and sufficient rainfall tropical forests can extend well beyond these limits. In some cases they can even extend into more mountainous territory.

Given such loose constraints, some scientists prefer to further divide these categories into the Neotropical (New World) and Paleotropical (Old World). Depending on the source and its definition of forest biomes, these ecosystems can contain nearly two-thirds of global biodiversity. With such a breadth of flora and fauna to be found, scientists highlight evolutionary differences found in Neotropical South America and Paleotropical Africa and Asia.

Continental separation can also go a long way in developing unique species or genetic variants. This is why, despite shared latitudes, there are strong differences between species found in the Amazon compared to those found in Daintree. The Asian region often can be further divided into Indo-Malayan and Australasian for similar reasons.

Rainfall is key to supporting these environments but is less reliable. Countries categorized by wet-dry seasons often experience some irregularity with precipitation. It is expected that in these regions annual rainfall will be greater than 5 feet.

Importantly, the dry season will not exceed 6 months and experience less than 0.5 feet of rain each month. Though these systems are not traditionally considered to have a consistently high atmospheric moisture content, they still influence global temperature and help provide a cooling effect.

Rainforests

Rainforests are defined by areas that receive anywhere from 79 to 394 inches of precipitation throughout the year. While they are largely concentrated within the tropics, they can also be found in temperate zones of the Americas, Australia, and Russia. In addition, these biomes must remain warm and frost-free. Mean temperatures in these areas have little variation, measuring between 20°C (68°F) to 25°C (77°F).

These systems are divided into four distinct layers: the emergent, the canopy, the understory, and the forest floor. Each layer possesses its own unique conditions and lifeforms. The emergent layer is at the top, with trees stretching as high as 200 ft tall. These trees often have sparse foliage along their trunks and bear waxy, highly absorbent leaves to aid with water retention. Species that you can expect to see as part of the emergent layer can include the Brazil nut tree, the Kapok tree, raptors, butterflies, and bats.

The canopy lies just below the emergent layer with a much thicker foliage that filters out the majority of sunlight and harsh weather to the lower layers. The canopy is typically about 20 ft in depth and many trees are equipped with water-repellent leaves to better sustain themselves in dark, damp, and humid conditions. Representing just a handful of the life in this layer as the most biodiverse are species like fig trees, howler monkeys, toucans, beetles, and lizards.

The understory is more intense in humidity and has less light. Plants here are smaller and have bigger leaves and, in fact, most houseplants sold commercially come from the understory! This layer is favored by flower, seed, and berry-producing flora, some of which produce strong smells to encourage pollination. Species that inhabit the understory can include jaguars, gorillas, mambas, tree frogs, and insects.

Finally, the forest floor. At this level, very little light penetrates which makes photosynthesis extremely difficult. Consequently, it is dominated by decomposing plants and bacteria to help nutrient cycling into the soil. This is not to say that there is no life as pigs, anteaters, scorpions, and more are also in this layer. Rivers will pass through the forest floor which can act as a magnet for biodiversity.

Similar to their tropical counterparts, rainforests also aid in global temperature control. Their high moisture content often produces clouds which help to reflect incoming sunlight and keep the atmosphere cool.

Tropical Rainforests

This term is used to describe forests that meet both rainfall and location criteria. Despite the importance of clarity, at times this term can be used broadly even if it is not precisely correct. The usage likely originated from a need for simplicity when conveying the importance of these biomes. The Amazon, the Congo, the Australasian (think of Indonesia and Papua New Guinea), and Sundaland (places like Borneo and Java) are all territories that fit into both categories.

Certainly, in most conversations in which these terms are used, others will understand the imagery and point in which you are trying to convey. However, the next time you’re discussing global trends like deforestation, conservation, or biodiversity, remember the key difference: Tropical forests are defined by their latitude whereas rainforests are defined by their precipitation.

Why Does Distinction Matter?

The emphasis between the key terms of this article is due to the importance and, at times, overlooked nature of tropical dry forests. These ecosystems account for nearly 40% of all tropical forests. In low-income households throughout Latin America and Africa, they can account for up to 63% of total income. They possess all the key characteristics laid out here along with additional determinants.

Located within the tropics, their dryland environment can experience 6 or more months with very low rainfall. These conditions also support lower-density fauna and unique biodiversity more adaptable to drought conditions. One critically endangered species that inhabit these systems are the cotton-top tamarin. Without more widespread education on the different types of forest ecosystems, their biodiversity, and relationship as income streams for local communities, we run the risk of permanent loss and damage to species habitats

ReWorld’s Efforts
One key reason to place such significance on the difference between these two subcategories: ReWorld is trying to save a tropical dry forest! This category of forest faces particular threat from deforestation and development, which unfortunately is a global trend not limited to South America. To learn more about how you can help preserve tropical dry forests, check out Reworld’s website, or our South American partner, Proyecto Titi.

Tropical Forests and Rainforests: What’s the Difference?