They provide timber, paper, and fuelwood, the main source of energy for more than half the world's people. Many agricultural crops originated in forests, where their wild relatives still evolve. Meanwhile forest trees, plants and animals provide a huge variety of foods and have been the source of many medicines, including quinine and the cancer-fighting drugs derived from the rosy periwinkle. Rural people, for example, make tanning products from bark, wicker furniture and baskets from rattan, and cooking oil, soap and varnish from oil seeds. Forest cover provides protection against wind erosion and desertification in arid areas, and trees and shrubs help maintain soil structure and fertility all over the world.
Forests help regulate the climate, weather and atmosphere and mitigate the greenhouse effect.
But, despite their value, the Earth's forests are being destroyed at an ever-increasing rate. Air pollution damages temperate forests in Europe and North America. When forests are destroyed, many plants and animals that depend on them are lost too. The first step towards extinction of a species is erosion of the genetic diversity that provides it with a wide enough range of genes to help it adapt and survive. The implications of genetic erosion for humans are also serious.