Animals—some found here and nowhere else—lose their habitat and may begin to die out. Plants that depend on the trees also begin to die out. The forest, once lush and wild, becomes more susceptible to fire, and the breakdown of the ecosystem follows.

The Penan, indigenous forest people of the Borneo rain forest, depend on the plants and animals found in and around the rain forest. As trees are cut down and animals leave the area or die off, the Penan face fewer and fewer resources, and their culture itself is on the verge of extinction.

Once numerous, there are now fewer than 30,000 orangutans left in the wild. The most visible symbol of the Borneo rain forest’s plight, the red ape represents the tremendous loss of biodiversity in rain forests around the world.

Although they cover less than 5 percent of the Earth’s land surface, rain forests are home to millions of species of animals, insects, and plants. That number is dwindling every day as rain forest land is destroyed.

In addition to animal species, we lose innumerable plant species as rain forests are cut down. Many modern medicines are derived from plants found in the rain forest—and the vast majority of tropical plants haven’t even been tested yet for their curative powers.

Greenhouse gases, like carbon dioxide, absorb surface radiation, heat up, and reradiate the energy back to the Earth’s surface. More burned or cut trees means more carbon dioxide, which means a warmer planet. And that’s not good, scientists say, since temperature changes could affect major climate patterns, alter species’ habitats, and have other unknown consequences.