Tropical rain forests are found near the earth’s equator and
contain an incredible variety of life. These lush forests are warm
year round and have high humidity and heavy rainfall almost
daily. Although they cover only about 2% of the earth’s land sur-
face, studies indicate that they contain up to half of the world’s
known terrestrial plant and animal species. For these reasons,
they make an excellent natural laboratory for the study of eco-
systems—communities of organisms interacting with one another
and with the physical environment of matter and energy in which
they live.
So far, at least half of these forests have been destroyed or
disturbed by humans cutting down trees, growing crops, grazing
cattle, and building settlements (Figure 3-1), and the degradation
of these centers of life (biodiversity) is increasing. Ecologists warn
that without strong conservation measures, most of these forests
will probably be gone or severely degraded within your lifetime.
Scientists project that disrupting these ecosystems will have
three major harmful effects. First, it will reduce the earth’s vital

Tropical Rain Forests Are Disappearing

Ecosystems: What Are They

and How Do They Work?

3

biodiversity by destroying or degrading the habitats of many

of their unique plant and animal species, thereby causing their

premature extinction. Second, it will help to accelerate cli-

mate change due to global warming by eliminating large areas

of trees faster than they can grow back, thereby reducing the

trees’ overall uptake of the greenhouse gas carbon dioxide.

Third, it will change regional weather patterns in ways

that will prevent the return of diverse tropical rain forests in

cleared or degraded areas. Once this tipping point is reached,

tropical rain forest in such areas will become less diverse tropical

grassland.

Ecosystems recycle materials and provide humans and other

organisms with essential natural services (Figure 1-3, p. 8) and

natural resources such as nutrients (Figure 1-4, p. 9). In this

chapter, we look more closely at how ecosystems work and how

human activities, such as stripping a large area of its trees, can

disrupt the cycling of nutrients within ecosystems and the flow of

energy through them.

Figure 3-1Natural capital degradation: satellite image of the loss of tropical rain forest, cleared for farming,
cattle grazing, and settlements, near the Bolivian city of Santa Cruz between June 1975 (left) and May 2003 (right).

UNEP/GRID-Sioux Falls UNEP/GRID-Sioux Falls

CORE CASE STUDY