What is a forest? There is no simple answer to this question. But the question is crucially important to an understanding of the current crisis. In order to answer it, we need first to answer two other questions. When does a group of trees make a forest? And how do we define a tree? The FAO provides the answer to both of these questions. According to its definition, a forest is a surface area of over 1.2 acres (0.5 hectares) composed of adjacent trees at least 16 feet (5 meters) tall when fully grown and whose foliage covers at least 10% of the ground surface. This definition gives us a starting point at least, although environmental organizations argue that it fails to distinguish between plantations and primary forests, and between forests that are in good health and those that have suffered significant damage.
Depending on the definitions, the total forested area of the planetís surface varies between 5.7 billion and 15 billion acres. Using the FAOís definition gives us a total of a little less than 10 billion acres, the equivalent of 30% of the Earthís land mass. Between 1990 and 2005, the planet lost 3% of its forest cover, which corresponds to 50,000 acres (20,000 hectares) a day. While forests are dwindling fast in certain countries such as Brazil and Indonesia, in others, especially in Europe, areas of woodland are increasing as a result of people moving away from the countryside, and China is witnessing the same phenomenon thanks to a massive tree-planting program.
The diversity of the situations is equaled only by that of the forests themselves. The first important distinction relates to primary forests, which are free of any evident impact by man and occupy only a third of the planet’s total forest cover, and secondary forests, which have been modified by human interference and are often less species-rich as a consequence. Forests are also classified in terms of ecosystems. A third of the world’s forest is taiga or boreal forest, associated with cold climates and extending from Alaska to Quebec, and from Scandinavia to Siberia. This type of forest is dominated by conifers (larch, pine, fir, spruce). Moist tropical forests occupy 6% of the planetary land mass and are associated with hot climates; they are the most productive and species-rich of our forests, home to two thirds or three quarters of all terrestrial species.