Tropical Forest Change

Tropical forest change includes a variety of negative and positive changes in the distribution and content of tropical forests caused by human and natural factors. The initial focus of study was on tropical deforestation, which merely consists of a reduction in forest area. This has since been complemented by the study of forest degradation, which involves a reduction in the quality of forests, as represented by a decline in their carbon density, biodiversity, tree density or other features, e.g., by selective logging. They are defined by FAO 1982 (cited under Monitoring with National Statistics) as “a complete clearing of tree formations. and their replacement by other use of the land,” and “less radical alterations of tree populations,” respectively. Their complementary roles are recognized by the Reducing Emissions from Deforestation and Forest Degradation (REDD+) mechanism of the United Nations Framework Convention on Climate Change. However, since the monitoring and modeling of forest degradation has not received the same depth of study as deforestation so far, it is not discussed in detail here. Increasing attention is now being paid to the expansion of tropical forests, or forestation. This takes the form of intentional tree planting on bare land (afforestation), and the regeneration of existing forests, through both natural and human assisted means (reforestation). Tropical forests encompass a wide range of different forest types in the tropics, a zone situated between the Tropics of Cancer and Capricorn (latitudes 23 degrees N and 23 degrees S, respectively) which consists of both the humid tropics, a band centerd on the Equator, and drier and more seasonal regions at higher latitudes. Tropical moist forests, found in the humid tropics, cover about 1,100 million hectares (ha) and have traditionally received most attention in monitoring and modeling studies, because they are the easiest to survey. Tropical dry forests, on the other hand, have been poorly studied, even though they may account for 40 percent of all tropical forest area. Tropical forests are of global importance because they cover about 1,800 million hectares (ha), or about 45 percent of all forests in the world, and contain about half of all plant species in the world and of all carbon stored in vegetation. There is still great uncertainty about the area of tropical forest and how rapidly it is changing. It is not the aim of this review to critically evaluate different estimates or give reasons for this uncertainty—references are provided below to direct readers to suitable sources on this. The aim instead is to provide an overview of the many decades of scholarship in this field, and to show how this has led to the accumulation of knowledge on changes in three of the most important attributes of tropical forest: area, carbon, and biodiversity.