Introduction

Holdridge (1947, 1967) developed a bioclimatic classification system by which the world's terrestrial biota may be categorized into approximately 120 life zones, each distinguished by climatic parameters that coincide with particular vegetational characteristics. Approximately 68 life zones are in the tropics and subtropics, of which 30 are dominated by forest of various types. Lugo, Schmidt & Brown (1981) estimated that 28 tropical and subtropical forested life zones are represented in Central America and the Caribbean, and 13 are found on the islands of the Caribbean. Despite this diversity, approximately half of the vegetation of Central America and the Caribbean is within the dry forest life zone (sensu Holdridge, 1967).

Dry forests are not infrequently referred to as deciduous forests, but the degree of deciduousness varies greatly (see below). Not all dry forests are conspicuously deciduous, and not all deciduous forests are dry forest. By Holdridge's criteria, tropical and subtropical dry forests are found in frost-free areas where mean annual biotemperature (a special calculation that reduces the effects of extreme temperatures) is above 17 °C, annual rainfall ranges from 250 to 2000 mm, and the ratio of potential evapotranspiration to precipitation is greater than one, to a maximum value of two. By these criteria, 49% (8.2 × 105 km2) of the vegetation of Central America and the Caribbean is considered dry forest (Brown & Lugo, 1980). Africa has the most dry forest (16.5 × 106 km2; 73% of the continent's vegetation); worldwide, about 42% of all intratropical vegetation is dry forest. Global patterns in dry forest distribution and overall ecological characteristics relative to wetter tropical and subtropical forest ecosystems were reviewed by Murphy & Lugo (1986a).