Today’s blog post is brought to you by Xander Kalna
Some of our students in the YCITYSCI Program asked about how plants survive in different climates. Today’s blog post is going to be about the plants that grow in the tropical rainforests! To begin, the tropics is the area between the Tropic of Cancer and the Tropic of Capricorn, which are two lines parallel with the equator. In the map above, you can see approximately where this area is by looking at the green color, which stands for “Tropical forest”. NASA’s Earth Observatory defines tropical rainforests as areas with an average daily temperature of 70-80 ℉ throughout the year, receives over 2 meters (or over 6 feet!) of rain a year, and are between the Tropic of Cancer and the Tropic of Capricorn.
To survive in the rainforest, plants have created many different adaptations to aid their survival. Since rainforests have so much rain, it actually washes away many nutrients from the soil. Due to this, many plants have extremely fast growth rates that enable them to immediately start growing once there is an opportunity. This helps the plant try to stay ahead of the competition of other plants trying to take the opportunity to grow as well. Along with the rain washing away nutrients, it also washes away soil. Many large trees in the rainforest grow buttress roots (like in the picture nearby or in this video!). If you have seen when a tree in the Midwest has roots that run along the surface of the soil, imagine if those roots stuck straight up out of the ground several feet! Buttress roots help support extremely large trees as well as help reduce erosion around them by catching and pooling runoff water and soil. Another unique root adaptation is stilt roots. Stilt roots are roots that grow from various parts of a tree toward the ground. Once they reach the ground they begin to thick and appear to be like another trunk or stem, helping support the plant structurally.
Talking about large trees, rainforests actually have some of the largest trees in the world. Since the rainforest has such an insanely high amount of plants, sunlight is oftentimes the prized resource. As such, many plants grow extremely tall to out reach their neighbors. Of course, other plants have figured out other ways to still compete with these extremely tall plants: growing as vines and growing without soil! While vine plants are not unique only to the tropical rainforests (you can find them in almost any forest in the world!), there are more vine plants growing in the tropics than anywhere else. Growing as a vine has the advantage of being able to grow from the soil and basically use the plants nearby as a ladder to reach the sunlight (see the photo with the large tree covered in vines!). Many vines grow tendrils that reach out and seek nearby plants to wrap around and pull the vine up (See it here!). Others grow suckers that attach the vine to other plants, kind of like the feet of lizards or squirrels. Even more unique than vine plants though are what are called epiphytes (or air plants!). Epiphytes are plants that can grow without soil, meaning that they will grow on the surface of other plants. Epiphytes include orchids, various “air plant” species, and mosses. These plants have root systems that don’t necessarily grow to gather water or nutrients, but they usually are grown to attach the epiphyte to whatever plant it is growing on. Since many epiphytes don’t have roots to collect water, they have small hairs on their leaves called trichomes that collect water from the air. Epiphytes usually reproduce by growing small clones of themselves that then break off and land elsewhere to start growing or by growing seeds similar to a dandelion that the wind can blow away to new areas.
In addition to special roots, some plants have managed to find a way to actually eat bugs! These plants are called carnivorous plants as they have evolved different ways to consume insects or other small mammals to collect nutrients that are in high demand like nitrogen and nitrates. Carnivorous plants catch their prey a few different ways such as the pitcher plant. Pitcher plants grow a unique leaf in the shape of a pitcher (see one of the pitchers in the photo!). Inside, the plant produces a liquid that attracts insects. The top of the pitcher though is slippery and hard for insects to hold onto, so they end up falling into the pitcher once they try to investigate the liquid. While the liquid is sweet or smells nice to the insects, it actually has digestive enzymes that break down the insect for the plant to absorb nutrients (kind of like your stomach and intestines!). Another way carnivorous plants capture insects is with flypaper traps, essentially using an extremely sticky substance to trap insects. In the tropics, the butterworts (Pinguicula) and the sundews (Drosera) use flypaper traps. The butterworts appear as any other small succulent plant, but it’s leaves are covered in tiny hairs that produce a sticky substance. This sticky substance traps insects against the leaf when they land on it looking for water or to rest. Sundews work in a similar fashion except the hairs on their leaves are bigger and the leaves themselves can usually move slightly! Once an insect lands on a sundew, the leaf it lands on may be able to actually move to wrap up the insect, further trapping it and letting the plant digest the insect faster.
References and Additional Resources
NASA’s Earth Observatory – https://earthobservatory.nasa.gov/biome/biorainforest.php
Sciencing.com, Plant Adaptations: Desert, Tropical Rainforest, Tundra – https://sciencing.com/plant-adaptations-desert-tropical-rainforest-tundra-13719230.html
Sciencing.com, Tropical Rain Forest Adaptations of Plants and Animals – https://sciencing.com/tropical-forest-adaptations-plants-animals-8514102.html
BBC, Tropical rainforests – https://www.bbc.co.uk/bitesize/guides/zx8n39q/revision/1
Wikipedia, Nepenthes – https://en.wikipedia.org/wiki/Nepenthes
Rainforest Map image by NASA’s Earth Observatory – https://earthobservatory.nasa.gov/biome/biorainforest.php