The primary threat to the health of forests around the world comes from humans. As human populations grow, three types of pressure are placed on forests. First, forests are cleared to provide land for agriculture or for the construction of new homes. This process has occurred almost continuously in the temperate regions for thousands of years, but it did not become common in tropical regions until the twentieth century. Often settlers level the forest and burn the fallen trees to clear land for farming (slash-and-burn agriculture) without the wood itself being used in any way. Tragically, the land thus exposed can become infer tile for farming within a few years. After a few years of steadily diminishing crops, the land is aban doned. With the protective forest cover removed, it may quickly become a barren, eroded wasteland.
Second, rising or marginalized populations in developing nations often depend on wood or charcoal as their primary fuel for cooking and for home heat. Forests are destroyed as mature trees are removed for fuel wood faster than natural growth can replace them. As the mature trees disappear, younger and younger growth is also removed, and eventually the forest is gone completely.
Finally, growing populations naturally demand more products derived from wood, which can include everything from lumber for construction to chemicals used in cancer research. Market forces can drive forest products companies to harvest more trees than is ecologically sound as stockholders focus on short-term individual profits rather than long-term environmental costs. The challenge to foresters, ecologists, and other scientists is to devise methods that allow humanity to continue to utilize the forest resources needed to survive without destroying the forests as complete and healthy ecosystems.
See also: Forest Ecology and Resources, Boreal Forest, Temperate Forest, Tropical Rain Forest
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