Shades of Green: Earth's Forests -- Biodiversity

Natural forests offer a far greater variety of habitats than "second-growth" forests that grow after people have cut down all the original trees. Large mammals especially need large expanses of natural forests. Over 2.5 times as many mammal species were found in an old-growth forest as in a second-growth forest in the same area of the United States. As more and more natural forests are cut down, the animals that depend on them disappear, and biodiversity is lost.

As would be expected, the larger an area of forest, the greater the number of species. There is simply more room in a large expanse of forest. This means that it can support a greater overall population of any particular kind of animal -- for example, beetles. A larger forest is likely to contain varied habitats and microclimates, and so this larger overall population of beetles will contain more individual species that are adapted for specific conditions.

A very general rule is that an area of forest that is ten times larger than another will have twice as many species.

In the tropical rainforest, a whole extra "layer" of diversity is added by the presence of mini-ecosystems right in the branches of trees. Epiphytes or "air plants" which grow in the tree canopy provide habitat for a variety of specialized insects and small animals. Photo by Maya Walters.

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