Rainforest Trees for Beginners
There are many thousands of kind of trees in the world's tropical rainforests. This page is about a few of the most important species, chosen to illustrate aspects of life in the forest.
A surprising number will be familiar to everyone, for the fruits, medicines and materials that they provide.
The Forest Layers
Forests are three-dimensional. If you climb a tree in any forest, you gradually rise through some very distinct layers, each of which is almost a separate world.
In a mature rainforest, this is especially true.
At ground level, the air is hot, damp and very still. Most of the sunlight has been absorbed by leaves above you and it is quite dark.
In contrast, at the highest level of the rainforest, trees are exposed to fierce tropical sun and the full effects of wind and rain.
These very different environments mean that very different kinds of tree grow in the rainforest.
On This Page You Will Find:
- Emergent trees described, with examples.
- Canopy trees, with examples.
- Understory trees, with examples.
Emergent Trees of the Rainforest
Emergent trees are those that rise above the canopy layer and stand out as individuals, visible for many miles. They often provide homes to eagles and other birds of prey.
Some special adaptions of emergent trees:
- very thick, very strong trunks that can climb two hundred feet into the air
- buttress roots to provide extra stability (see photo below)
- canopy trees and emergent trees live a long time and need to resist damage from grazing animals and insects. They produce special chemicals in their tissues that make them bad to eat, like tannins or camphor. Some even use cyanide to poison animals that try to eat them!
Kapoc (Ceiba Pentandra)
One of the largest trees on the planet is the Kapoc. It can grow to two hundred feet tall and have a trunk diameter of nine feet.
The Kapoc came from South America originally, but is now found in many rainforests around the world.
Emergent trees have a very different world to live in than other rainforest trees. Neither wind nor sun reach far beneath the canopy but a tree like the Kapoc is fully exposed to both.
The Kapoc tree uses the power of the wind to disperse its extraordinarily hairy seeds rather like a dandelion or a thistle.
Useful description of the ecology of the tree: http://lee.ifas.ufl.edu/Hort/GardenPubsAZ/Ceiba_pentandra.pdf
Shorea Gratissima (Dipterocarp Family)
The pair of giants pictured above are both Shorea gratissima.
Shorea species are members of the dipterocarp family and dipterocarps are the most common tree in the rainforests of Southeast Asia. In the canopy layer, more than one in ten trees will belong to this family.
In rainforests elsewhere in the world they will be not be found at all.
The Dipterocarpaceae are easily recognized by the fruits that they produce. Each fruit has wings which makes them spin like helicopter blades as they fall. Some of these fruit are pictured below.
Another way of recognizing these trees is by looking at the arrangement of their leaves. From below, you can see a characteristic, branching, cauliflower-like pattern (photo above). The branches start at a high level, at the top of very straight trunks.
All dipterocarps have buttress roots, although Shorea gratissima has only small ones.
An unusual feature of diptoercarps is that they do not flower every year. Instead they mass flower at irregular intervals spaced at 3 to 7 years. It seems that the unusual weather conditions of an El Nino year triggers flowering.
Mass flowering at irregular intervals means that animals like wild pigs or monkeys cannot eat the entire crop and some seeds will survive to grow as new trees.
Canopy Trees of the Rainforest
The canopy layer is the most productive layer of the rainforest. It absorbs most of the light from the sun and leaves here use that light to produce the food that powers the forest.
Most rainforest animals live in this layer, from monkeys to birds and butterflies to snakes.
Annonaceae: Custard Apple Trees
Custard apple trees have a characteristic edible fruit loved by both people and forest animals like squirrels, birds and monkeys. Some of these fruits remind me of chocolate candy bars! They are even sweeter than a banana.
Some species of the Annonaceae family are canopy trees in various parts of the world such as the Philippines, Central America and Africa.
Anacardium Excelsum: Wild Cashew Nut Tree
This tree comes from Central and South America where it is a canopy tree valued for its delicious nuts.
It can grow up to 120 feet tall.
Domesticated cashew nut trees can be quite small -- no more than twenty feet tall. This makes harvesting the nuts much easier!
Shorea Acuminata (Dipterocarpaceae)
This tree is a close relative of the emergent tree, Shorea gratissima, described already, but it is shorter and confined to the canopy.
It has a distinct smooth grey/white trunk that stands out at a distance in the dim light beneath the canopy.
Like all dipterocarps, it produces distinctive winged nuts and flowers at erratic intervals.
If you walk in a rainforest in Thailand or Malaysia, it is the tree that you are most likely to see.
Other Tree Families Important in Rainforest Canopies
Rubiaceae, Lauraceae, Leguminosae, Rutaceae, Apocynaceae and Solanaceae.
Epiphytes: plants that grow on other plants.
It is not just the leaves of the canopy trees that are important for food production. Many smaller plants live on the branches and trunks of trees. At first, the surfaces are colonized by mosses and lichens. The death of these plants makes a kind of compost where plants like orchids and bromeliads can take hold.
Together with the leaves of the tree, Epiphytes make a sort of 'garden in the sky' producing food and hosting animals of all kinds.
Understory Trees of the Rainforest
Trees that grow in the understory are often called pioneer trees. They are the first trees to grow if the mature forest is damaged by fire or storm, or a clearing is created by a tree dying of disease or old age.
As soon as light reaches the forest floor, seeds germinate and the race is on.
Pioneer trees grow faster than canopy trees partly because they invest less effort in defenses against animals that want to eat them or molds, bacteria and viruses that can infect them.
The slower growing giants of the rainforest like the Kapoc and the Dipterocarpacae overtake the pioneer trees eventually, blocking out the light and stopping their growth.
Understory Trees as Food Providers
Many important sorces of food are found in the understory such as bananas, mango, papaya and oil palm.
Spices like cinnamon and medicines like quinine also come from rainforest trees.
Banana trees are perfectly adapted to the understory.
They are fast growing to take advantage of any temporary gaps that appear in the canopy and let in the sun.
The large leaves will catch any light that is available.
Oil Palm (Elaeis guineensis)
Many kinds of palm tree grow in the understory. One of the most notable is the oil palm.
It is a native of West Africa where it grows wild, mainly on the edges of rivers or in freshwater swamps.
It has been transported all over the tropics in the last fifty years because it is an extremely valuable source of oil used for cooking and in cosmetics.
Although it has created a lot of wealth for farmers in the tropics, it has also had bad effects.
The profits to be made from oil palm cultivation have been a major reason for the clearance of rainforests around the world, but most especially in Malaysia and Indonesia.
Many animals, like orangutans, that live in rainforests now face extinction as a direct result of oil palm production.
'Strangler fig' is a name applied to many different species of fig tree. These trees grow around any upright structures, such as rocks, other trees and even buildings.
The name 'strangler' is apt since many trees are killed by complete enclosure.
The fig fruit is one of the most important foods of fruit bats.The large number of species in a rainforest means that a bat can almost always find at least one kind of fig in the fruiting stage.
Human beings can eat many kinds of strangler fig. Early settlers in Florida used Florida Strangler Fig flowers to produce dies and roots for bowstrings and fishing lines.
Cecropia: A Tree Defended by Fierce Ants
Like many plants in the tropics, Cecropia trees have ants that defend them against grazing animals and insects that try to eat them. The ants of the Cecropia tree even attack other plants that might try to overgrow their home.
The tree is hollow and the ants make their nests inside them, well protected from rain and sun. The tree also produces a sugary sap for the ants to feed on.
This kind of relationship, where two living things live together in a way that is helpful to both parties, is called symbiotic.
Pioneer Trees Are Often Weeds
If you live in the tropics, Cecropia species include the weeds that cause most problem for farmers and gardeners. After a single year a tree can grow to a height of several feet.
Looking out of my window, right now, I can see a huge stand of Cecropia that has colonized the backyard of a house left unattended for only a few months.
Understory Trees of the Laurel Family
Laurel trees are a familiar sight in Europe and the US and give us bay leaves for cooking.
Laurels also include the rainforest trees that produce cinnamon, avocado, cassia and camphor.
How Do Rainforest Trees Reproduce?
Trees reproduce in a similar way to flowering plants with pollen spread by wind or insects, fertilizing the female parts of the flower.
Seeds are produced that are spread far and wide by wind, animals, water or gravity.
- Wind: the Kapok has cotton-like hairs attached to the seed that catch the wind.
- Animals: Custard Apple trees have sumptuous fruit that animals eat. The hard, indigestible seeds inside the fruit pass straight through the animals and usually end up far away from where they are eaten.
- Water: many palm trees that live near water drop seeds that float to be spread by the currents.
- Gravity: heavy fruits fall as they mature. Some will bounce from lower branches or roll down hills to get some distance from the tree.
Studying Rainforest Trees
About a quarter of our medicines come from plants but only one in a hundred tropical plants have been studied for their health benefits.
Studying the trees and plants of the rainforest before they disappear is essential.
Rainforests are difficult to study for a whole number of reasons.
The most productive part of the forest is high above ground level. Often, scientists are forced to climb ropes to gather data.
Rainforests are often very hard to move through because of dense undergrowth.
The environment takes a toll on human health. It is very hot and humid. Many plants have spines and cuts are easily infected. Malaria, is a serious issue in most jungle environments.
One way to study the rainforest (and also accommodate school kids and tourists) is to build a canopy walkway. The one pictured below is in Trang Province, Thailand.