What Causes the High Rainforest Biodiversity?

Our rainforests are the oldest ecosystems on Earth. Some of them have been around for more than 70 million years. Despite covering only 6% of the Earth´s surface rainforests contain the majority of animal and plant species of our world. Just to give you an impression of how diverse rainforests actually are: You can find “1,500 flowering plants, 750 species of trees, 400 species of birds and 150 species of butterflies” (National Geographic, s.a.) in a 10-square-kilometre rainforest. ¹ But why are rainforests so extremely diverse? In this blog post, I will examine three reasons for the huge rainforest biodiversity.

Reason 1 : The layer structure

Rainforests mostly have a four-layer structure. They differ in terms of water level, air circulation and sunlight. The top layer is also referred to as the emergent layer. Here are some trees that can reach heights of 60 metres. ¹

The canopy is the layer beneath the emergent layer. It creates a thick vegetation layer that acts as a roof over the last two layers. The canopy creates a humid and dark environment by blocking wind and sunlight. This makes the canopy especially important for rainforest biodiversity because it creates the ideal climate for the plants below. To adapt to this environment trees, produce glossy leaves with water-repellant tips. ¹

The Understory Layer and the Forest Floor Layer are the two lowest layers. The understory layer is characterized by small plants with large leaves that catch the remaining sunlight beneath the canopy layer. Plants find it difficult to grow on the forest floor layer due to its darkness. It is, however, an important decay zone for organic matter, attracting decomposers such as worms and fungi. ¹

The four layers can be distinguished based on different microclimatic conditions that do not represent an uncrossable barrier. Species interact with each other across the layers. ¹

Reason 2: A wealth of nutrients

As I mentioned in previous paragraphs, the forest floor layer is rich in decomposers. Fallen leaves decompose quickly. Organisms such as termites, worms, slugs and fungi break down organic matter in its nutrients. Shallow tree roots absorb these nutrients and the decomposers supply nourishment for predators. ¹

However, according to the book Tropical Rainforests: Latin American Nature and Society in Transition, tropical rainforests have poor soil. This is partly the case because of the high acidity and clay content of the soil, which prevents trees from absorbing nutrients from the soil. ²

The reason why the huge amount of nutrients still leads to biodiversity is that heavy rains wash nutrients almost directly into the trees, without much entering the soil. ³

Reason 3: A favourable climate

Tropical rainforests, as the name implies, are primarily found in the tropics. Because of the almost direct solar radiation, the tropics have high temperatures. ¹

High temperatures create a lot of humidity, which leads to a lot of rain. “Tropical rainforests are so warm and moist that they produce as much as 75% of their own rain through evaporation and transpiration” (National Geographic, s.a.). The tropics’ abundant sunlight and moisture create ideal conditions for biodiversity. ¹

Conclusion

The three reasons behind the high rainforest biodiversity are the layer structure, the wealth of nutrients, and the favourable climate. This biodiversity provides important ecosystem services for us as regulating the climate. If you’re interested in learning more about the ecosystem services of rainforests, check out my blog post on the role of forests in water cycles how the rainforest ecosystem helps to create rain.

References:

1. National Geographic, s.a. Rainforest. Available at: https://education.nationalgeographic.org/resource/rain-forest [27.01.2023].
2. Place, S.E, 2001. Tropical Rainforests: Latin American Nature and Society. Wilmington: SR books.
3. Baird, C. S., 2013. What makes the soil in tropical rainforests so rich? Available at : https://www.wtamu.edu/~cbaird/sq/2013/07/12/what-makes-the-soil-in-tropical-rainforests-so-rich/ [27.01.2023].