Maidenhair Trees (Ginkgo biloba) evolved hundreds of millions of years ago. They are the only remaining survivor of their ancient, and once abundant, plant family. They are now thought to be extinct in the wild, and the individuals that remain have all been planted -- they are now popular ornamental trees because of their resistance to pollution, drought, pests, and their ability to grow in a variety of soil conditions. Photo by Maya Walters.

Biodiversity is built over millions of years and extremely diverse habitats such as tropical rainforests have taken long stretches of geologic time to develop. That's why the extinction of species is such an important issue: once they're gone, not only are they gone forever, but it takes millions of years for new species to evolve in their place. Some extinctions are natural, but a variety of human activities have vastly increased the numbers of species disappearing every day. Habitat destruction is the main cause, especially since the richest habitats with the most species, such as tropical forests, are being destroyed at the fastest pace. Extinction rates are now hundreds or even thousands of times higher than before humans came to be so numerous. Some scientists have estimated that as many as one fifth of all species alive today could be extinct or nearly extinct by the year 2020.

If one species goes extinct, all other plants and animals in the ecosystem are affected. If insects and animals that are essential for pollination are removed, flowering plants suffer, and in turn so do the animals that feed on them. Photo by Maya Walters.

What effects does the loss of biodiversity have on forests, and on humans? The loss of even one species can ruin an entire forest ecosystem of plants and animals. The animals that depended on this vanished species as prey have now lost their food source. In turn, the animals that it fed on have lost a predator, and these species often undergo population explosions which are devastating for the plants or animals that they feed on.

Species in the tropical rainforest are some of the most at-risk, not only because their habitat is being destroyed so quickly, but because most have very limited ranges. There is enormous biodiversity in the rainforest, but many of these countless species exist only in a few hectares of forest and nowhere else in the world. If this area of forest is burned or cut, this species vanishes forever. Other species are scattered widely through larger areas, but if the forest is fragmented into small pieces surrounded by agriculture and development, there are not enough individuals in each area to reproduce.

Tropical forests have the greatest biodiversity of any habitat in the world; they are also being cleared at an increasing pace. Photo by Maya Walters. Tropical rainforests likely once covered nearly 25 million square miles. Estimates vary widely on how much is being lost every year. Many human activities directly or indirectly contribute to deforestation, and almost everywhere that there are lots of people, the forest is being destroyed. Millions of people now live in moist tropical regions. In the past forty years alone, 90 percent of the wet lowland forests in western Ecuador (a country on the west coast of South America) have been cleared. These vanished forests were once home to 10,000 species of plants, and about 2,500 of these were found nowhere else in the world.

Even the remaining North American forests are still being cleared for new development. Photo credit Corel Photo Clipart CD.

While the tropical forests are disappearing fast, others have already vanished. Forests right in the United States once covered millions of acres, but with the pressures of more and more people settling the area, they disappeared in just a few decades. Logging of the Southeastern forests led to the extinction of species such as the Carolina parakeet and the ivory-billed woodpecker. The Carolina parakeet was the only parrot native to the United States, and was once common throughout these Eastern broadleaf forests. The last individual died in captivity around the same time as the last passenger pigeon (likely once the most abundant bird species on earth) died in its cage at the same zoo. The ivory-billed woodpecker was one of the largest and most studied woodpeckers, although it was never very abundant. Each pair of breeding birds required as much as 2000 acres of territory in a mature forest. This made them especially susceptible to habitat loss, and led to their extinction in 1951.