The biodiversity of plants in the rainforest is staggering. Some rainforests have more species of plant than entire continents, and a single tree in the rainforest may contain more species of epiphyte (plants that grow on other plants) than most countries. But why are there so many plants in the rainforest?
Biodiversity is simply a measure of the variety of life in a given area. Rainforests are the most biodiverse places on earth, from the Amazon River Basin to the African lowlands. Tropical forests and temperate rainforest alike carry more than their fair share of species. But why?
Why are there so many plants in the rainforest?
Of course, it’s pretty challenging to prove that a given factor causes the biodiversity of a rainforest. We can only look at the traits that rainforests and other biodiverse places have in common, and compare that to less-diverse areas.
In other words, our answer to this question is one of “correlation, not causation.” But it’s the best we’ve got!
Stable Year-Round Environment
It’s far easier to adapt to an environment if it stays the same all year long. Both plant and animal species seem to be more biodiverse in temperate or tropical environments.
Rainforests lack the severe rainy/dry season changes characteristic of deserts and savannah, helping explain why not all tropical climates are so biodiverse. “Learning,” in the evolutionary sense, how to deal with tough winters is hard – so fewer species survive in places with seasonal variation.
Rainforests Have Few Extremes
Going along with the idea of a stable year-round environment, most rainforests don’t have much for extremes. The seasonal changes are less dramatic. If there are no annual extremes to kill off different species, more species can survive!
Even the temperate rainforests of Washington, British Columbia, and Alaska are less extreme than neighboring ecosystems. Extreme heat, cold, wind, drought, or flooding can all kill off species and reduce biodiversity. Rainforests lack these killers.
Rainforests are Warm and Humid
Many different plant species (as well as amphibians and some other animals) do best in warm, humid environments. Humid air helps keep plants from losing water through their pores (that’s part of the reason that desert plants have so many weird adaptations). The warmth is also good for plants.
Again, even the temperate rainforests of Alaska are much warmer than the surrounding areas!
Sunlight Keeps Plants Happy
Most rainforests lie along the equator, meaning they get good year-round sunlight. Since most plants need sunlight to survive, this helps more plants thrive in the rainforest.
3D Space Allows for More Plants
Rainforests have more space — and I’m not just talking on the ground level. Even in an area of rainforest that only has an acre of forest floor, the tree species form a tall canopy that allows for lots of epiphytes.
Ferns, mosses, bromeliads, orchids, vines, and many other plants can all survive in the rainforest thanks to this unique 3D habitat. Of course, abundant rainfall and humid temperatures also help these epiphytes survive.
There’s Plenty of Water to Go Around
Rainforests get a lot of rain — that’s no secret. This means that water isn’t a huge limiting factor for the number of individuals that fit into a given area of the tropical rainforests. Paired with plenty of sunlight, a plant-friendly climate, and lots of 3D space, there’s simply a lot going for rainforest plants.
Have you noticed the incredible diversity of the Amazon Rainforest or other rainforests around the world? What did you think was a factor?