Definitions and Classifications of Forest Ecosystems
Forests, which can be defined as woody plant communities in areas that are large enough to modify the local environment and microclimate (Chang, 2002), currently cover 3.8 billion hectares, roughly 30% of the Earth's land surface (FAO, 2010). Approximately 25% of the world's forested area is located in Europe, followed by South America (21%), North and Central America (17%), Africa (17%), Asia (15%), and Oceania (5%) (Table 1.1). The most extensive forest biomes are tropical, boreal, and temperate (Figure 1.1). Tropical forests cover approximately 1.76 billion hectares (or 42% of the world's forested area), followed by boreal forests with their roughly 1.37 billion hectares (or ~33% of the world's forests), and temperate forests (1.04 billion hectares, or 25% of the world's forested areas) (IPCC, 2000).
Forest ecosystems play a fundamental role in the dynamics of the Earth system and provide services of great environmental, societal, and economic value. They are a major determinant of the regional and global climate (Chapter 2), modulate water and nutrient cycling (Chapter 3), and provide invaluable resources and services (Chapter 5) that have played a crucial role for the social, economic, and cultural development of several civilizations. Depending on how resources derived from forests are used, they can be either renewable (i.e., not depleted) or nonrenewable (Chang, 2002). Moreover, the rise and fall of several civilizations in human history have been determined by their use and overuse of forests (Box 1.1).
This book is concerned with the ongoing phenomenon of global deforestation (Box 1.2). This Introduction and the following chapters will discuss the major drivers along with the environmental and societal implications of deforestation. It will also analyze social-environmental processes that affect the stability and resilience of forest ecosystems and their ability to recover after deforestation.
Box 1.1 Deforestation and the Collapse of Past Civilizations
Geographers and anthropologists have often related the decline of past civilizations to environmental degradation resulting from deforestation. Deforestation might have triggered the collapse of the Viking, Maya, Anasazi, and Rapa Nui civilizations (Diamond, 2005; Turner and Sabloff, 2012). In most of these cases, deforestation enhanced soil erosion, thereby leading to the permanent loss of soil resources. In Chapter 4, we will discuss some positive feedbacks that could prevent forest regeneration.