Rainforests play a critical role in Earth’s biodiversity. Despite covering only 2 percent of Earth’s surface, rainforests harbor an estimated 50 percent of all animals and approximately two-thirds of all plant species. Biodiversity is the degree of variation among life on a genetic, species, or ecological level and is essential for the resilience, productivity, and survival of Earth’s ecosystems. This blog will explore the biodiversity of two types of rainforests, tropical rainforests and temperate rainforests, and how their differing biodiversities can be attributed to their unique characteristics.

Two Types of Rainforests: Tropical vs. Temperate Rainforest

A rainforest is an area that is densely composed of tall, lush trees that receive at least 1750 millimeters, or a little more than 5.5 feet, of rainfall on an annual basis. The most widely known rainforests are tropical rainforests, which are found in tropic zones of the Earth. Tropic zones are located between the Tropic of Cancer in the Northern Hemisphere and the Tropic of Capricorn in the Southern Hemisphere. Temperate rainforests are found in the more coastal, temperate regions of the Earth such as New Zealand, the Pacific Northwest of North America, or Tasmania. Both types of forests are essential for sustaining the Earth’s biodiversity. 

Proximity to the Equator and Biodiversity

Geographic location has an immense impact on a rainforests’ biodiversity. The location of a rainforest dictates how much solar energy it receives. Higher amounts of solar energy often lead to higher biodiversity. Since tropical rainforests are located near the equator and receive lots of sunlight throughout the year, tropical rainforest biodiversity tends to be higher than temperate rainforest biodiversity. 

Their proximity to the equator also means tropical rainforests experience consistent, stabilized warm temperatures year-round. Throughout the year, tropical temperatures can reach around 77 to 86°F (25 to 30°C) and humidity levels can surpass around 77%. These stable temperatures increase the rates of photosynthesis and decomposition, leading to flourishing vegetation. The combination of stable, humid temperatures and water availability allows tropical rainforest biodiversity to flourish. 

Temperate rainforests are located further from the equator and experience cooler-temperatures. Rather than having constant warm temperatures, temperate rainforests experience all four seasons with cold winters and hot summers. By experiencing all four seasons, temperatures can range anywhere between 40°F and 70°F (4°C to 21°C). With a more dynamic and varying climate, temperate rainforests often undergo a temporary loss of species which decreases their ecological diversity. 

How Glaciation Affects Rainforest Biodiversity

Tropical rainforests have also been largely unaffected by glaciation, the process of glaciers forming, traveling, and reshaping the Earth’s surface, for millions of years. This has allowed tropical rainforests to avoid major disruptions in their climate and avoid species extinctions. 

On the other hand, temperate rainforests have been disrupted by glaciation, having suffered from extreme climatic disturbance and species loss throughout history. Although temperate rainforests typically don’t receive as much rainfall as tropical forests, they still can receive plentiful rainfall and experience fog and mist to sustain their moisture levels. 

Tree Structure and Flora

The solar energy that a rainforest receives based on its geographic location has a crucial impact on its tree structure and flora. Tropical and temperate rainforests differ greatly in structure. Where tropical rainforests are comprised of tall, dense vines and multi-layered canopies, temperate rainforests have shorter trees and moss covering tree branches and the forest floor. The forests’ structures greatly impact their species variety.

Tropical Rainforests’ Layered Structure

Tropical rainforests are known for their prosperous and multi-layered vegetation with towering trees, thick vines, and numerous epiphytes. The vegetation in tropical rainforests is so dense that plants grow in layers. Within each layer of the forest, different species can grow. This intricate structure creates a vast array of habitats and microclimates that can sustain different species and allow species to coexist within the same area. 

Most of the species in tropical rainforests can be found in the canopies, which are the dense, upper layers of the forest. The canopy acts as a roof that protects the animals and plants living beneath it and creates a dark, humid environment on the forest floor. Because of the constant warm temperatures and plentiful rainfall, the forest floor often has eroded, nutrient-poor soil. This may seem like a negative impact on tropical rainforests; however, plant species have adapted to survive in these nutrient-poor environments. 

Each layer in the tropical rainforest, starting from the forest floor to the highest canopy, offers a unique habitat where different species can grow. The high humidity, varying light levels, and dynamic soil conditions further contribute to the plethora of habitats existing in the tropical forest. This structural complexity allows tropical rainforest biodiversity to reach exceptionally high levels.

Temperate Rainforests’ Open Structure

Although not as biodiverse as tropical rainforests, temperate rainforests still have unique structures that nourish many different types of plant and animal species. Because of cooler temperatures, temperate forest trees are limited in height and are characterized by moss-covered branches. These forests have a more open, spacious canopy structure than the tropical rainforests’ dense, complex canopy structure. This allows more sunlight to touch the forest floor, where the majority of the plant species are located. Despite temperate rainforest biodiversity being generally lower, temperate rainforests have more nutrient-rich soil, which allows plant diversity to increase in these environments. Trees commonly found in temperate rainforests include redwoods, cedars, oak, and maple trees. 

Speciation and Fauna

The structure and primary productivity of plants in rainforests gives rise to speciation over time. 

Speciation is an evolutionary process where new species emerge from their original lineage over time. This occurs when a group within a species separates from other members to meet the demands of a different environment and develops their own distinctive characteristics. This process occurs frequently in tropical rainforests, remarkably increasing their ecological richness. Based on the general pattern of “the taller the trees, the more the layers, the more the niches, and the more the species,” tropical forests are widely diverse while temperate forests are more ecologically succinct. 

Animal Biodiversity in Tropical Rainforests

The elaborate, multi-layered canopy structure of tropical rainforests promotes niche species to develop over time. Each layer is its own nuanced microhabitat that supports the different needs of different species. Niche specialization occurs when species are able to adapt to an environment and utilize certain resources in distinct ways. This process reduces competition amongst species, allowing them to prosper. For example, several bird species can cohabitate on one layer within the tropical rainforest canopy by feeding on different types of seeds or insects found. This variety of nutrients reduces competition of resources for animals. Animals such as monkeys, toucans, and poison dart frogs are animals that are commonly found in tropical rainforests and benefit from this layered structure. 

In addition, the steady heat and generous rainfall provides bountiful resources for different species, contributing to the biodiversity of tropical rainforests. These consistent conditions are conducive for species to specialize and fulfill specific roles within an ecosystem, rather than needing to become generalists in less stable climates, such as temperate rainforests. 

Animal Biodiversity in Temperate Rainforests

Temperate rainforests have shorter trees and fewer forest layers than their tropical counterparts. This leads to less niche specialization since there are less unique microhabitats where different species find the resources they need to survive. Their varying climatic conditions also limit biodiversity, since species must become generalists in order to adapt to a broader range of conditions. Animals commonly found in temperate forests are owls, salmon, cougars, and black bears. 

Despite their differences in biodiversity, both types of forests are home to rare and endemic species. Endemic species are species that can only be found in a specific geographic area. These species contribute to the astonishing nature of tropical and temperate rainforests. 

Famous Tropical Rainforests: The Amazon Rainforest

The Amazon Rainforest is the world’s largest tropical rainforest, located in South America. It constitutes an estimated 2.1 million square miles and is considered the most species rich forest in the world. Not only does it contain approximately a third of the world’s species, but it is also home to a quarter of the world’s freshwater and 200 indigenous and traditional communities. Additionally, the Amazon River, the largest river in volume in the world, flows through the rainforest. This further highlights the Amazon Rainforest’s astounding biodiversity and importance to the world’s environmental health. 

Amazon Rainforest Species

Below are a few of the extraordinary species that are predominantly found in the Amazon Rainforest:

Amazon River Dolphin: Amazon River Dolphins are famously known for their pink skin when they mature and are also named the “Pink River Dolphin” or the “Boto.” It is the largest of all other river dolphin species and does not survive in salt water. They use whistling tones for communication that are unique compared to other dolphin species.

Giant Otter: The Giant Otter is the morphologically longest member of the weasel family. It can grow up to nearly 6 feet and has dense fur that makes it impermeable to water. They are able to swim 330 feet in less than 30 seconds. 

Bald Uakari: The Bald Uakari is a type of monkey and is characterized by its distinct bald, red face. They spend around 90% of their time dwelling in high canopies and feed on a variety of plants and insects. 

Famous Temperate Rainforests: The Tongass National Forest

The largest temperate rainforest in the world is the Tongass National Forest, located in Alaska. It is 26,250 square miles in size and stretches along the coastline of Southeast Alaska. It surrounds the popular Inside Passage and contains national monuments, such as Admiralty Island and Fjords. The forest has been home to indigenous groups such as the Tlingit, Haida, and Tsishian Peoples, for thousands of years. 

Tongass National Forest Wildlife

Some famous species that are primarily found in the Tongass National Forest include:

Alexander Archipelago Wolf: The Alexander Archipelago, named to honor the Tsar Alexander II of Russia in 1867, is a group of over a thousand islands that span the coast of Southeast Alaska. The Alexander Archipelago wolves are a subspecies of the gray wolf and have a lifespan of 6-8 years. 

Bald Eagle: The Tongass National Forest is home to the majority of the bald eagles in the world. Bald eagles have a long lifespan, with the oldest bald eagle recorded living up to 38 years. It was declared the American national bird in 1782. Their diet is primarily made up of fish, other birds, snakes, and lizards. 

Sitka Black-tailed Deer: The Sitka Black-tailed Deer are a subspecies of mule deer. They are characterized by their short, black tail and typically around 3 feet in height. They are hunted by wolves, coyotes, mountain lions, and bears, and primarily eat vegetation such as grasses, tree leaves, and shrubs. 

Biodiversity in tropical and temperate rainforests make them home to innumerous rare and remarkable species. This underscores the importance of learning more about these rainforests and protecting their vitalities. 

Learn More About Rainforests

Tropical rainforests and temperate rainforests are both essential to the health of the planet, yet they are at risk for destruction. These forests face threats such as deforestation, climate change, and habitat fragmentation. These threats can lead to the extinction of plants and animals that live in these forests, thus severely depleting the well-being of Earth’s ecosystem. Therefore, learning about the biodiversity of these forests are essential for their safety. World of Difference: The Amazon is a lesson that is part of the Counting on People: K-5 Activities for Global Citizenship curriculum that teaches students the importance of preserving the biodiversity and richness of temperate and tropical forests. Students compare the biodiversity of temperate and tropical forests and explore the impacts of human-caused deforestation. This lesson not only presents fundamental science, math, and social studies concepts, but also fosters key skills for students to become strong stewards of the Earth. 

Image credits: Tropical rainforest in Johor Bahru (Sofiya Muntyan from Russia, CC BY 2.0, via Wikimedia Commons); Aerial view of temperate rainforest (Temperate rainforest from above by Ruth Hartnup is licensed under CC BY 2.0); Rainforest vegetation (Tropical Rainforest, Queensland by Steven Penton is licensed under CC BY 2.0); Temperate rainforest trees (John Haynes, Typical temperate rainforest trees, CC BY-SA 2.0, via Wikimedia Commons); Toucan (Rainforest Resident by LASZLO ILYES is licensed under CC BY 2.0); Blackbear cub (Blackbear Cub by GlacierNPS is Public domain); River in the Amazon rainforest (Jlwad, CC BY-SA 4.0, via Wikimedia Commons); River dolphin (Diogo Luiz, CC BY-SA 4.0, via Wikimedia Commons); Giant otters (Giant Otters (Pteronura brasiliensis) resting in the sun … by Bernard DUPONT is licensed under CC BY-SA 2.0); Red bald uakari (Kevin O’Connel, CC BY 2.0, via Wikimedia Commons); Waterline of Tongass National Forest (Best of the Tongass National Forest by Forest Service Alaska Region, USDA is Public domain); Alexander Archipelago wolf (Alexander Archipelago wolf by Bob Armstrong is licensed under CC BY-NC-ND 2.0, via U.S. Fish & Wildlife Service); Bald eagle in Tongass National Forest (Bald eagle taking off from iceberg by Forest Service, USDA is Public domain); Deer (Sitka black tail deer Alaska zoo Anchorage by Watts is licensed under CC BY 2.0.)