Introduction

Conversion of tropical dry forest to agriculture and pasture is occurring at alarming rates, and entails nearly total destruction of forest structure and composition, and disruption of ecosystem functions. In this chapter the driving forces of this process are briefly discussed, the general pattern of the transformation is described, and the consequences of the conversion for ecosystem functioning are analysed in some detail. Particular attention is given to specific environmental conditions and management practices that determine or alter the extent of the perturbation.

Causes and patterns of forest conversion

Driving forces

Janzen (1986) considers dry forest as the ‘most endangered major tropical ecosystem’ because the distribution of these forests has been reduced to a small fraction of the original area. Less than 0.1% of the original dry forest has conservation status in Pacific Mesoamerica. The status of dry forest is just as critical, or worse, for regions of Australia, Southeast Asia, Africa, and major parts of South America (Janzen, 1986, 1988). Actual rates and the extent of dry forest conversion are analysed by Murphy & Lugo (Chapter 2). They have pointed out that we will never know the true original or potential extent of dry forest because many savannas and scrub or thorn woodlands are thought to be derived from disturbed dry forest (Murphy & Lugo, 1986; see Menaut, Lepage & Abbadie, Chapter 4).

There are ecological, social, political and economic factors involved in forest clearing for agricultural purposes. Often subsistence farmers are blamed for the massive deforestation in the tropics, but other groups are also involved in this process. According to Thapa & Weber (1990), those responsible for deforestation can be broadly categorized into three main groups.