Introduction

Many studies of neotropical dry forest have tended to treat them in a very broad context, typically focusing on how they relate to or are different from moist or wet forests (e.g. Holdridge et al., 1971; Rzedowski, 1978; Gentry, 1982a, 1988; Hartshorn, 1983). Others have taken them as a relatively tractable surrogate for the more diverse moist or wet forests (e.g. Janzen, 1983, 1984, 1988; Hubbell, 1979) where taxonomy often poses severe limitations for the resolution of biologically interesting questions. Other authors have concentrated on the interesting physiological adaptations of dry forest organisms to seasonal water stress (e.g. Medina, Chapter 9; Holbrook, Whitbeck & Mooney, Chapter 10 and included references) or on various aspects of nutrient flow and biomass (e.g. Lugo et al. 1978; Murphy & Lugo 1986a, b). In addition there have been floristic and community ecological studies of individual dry forests (e.g. Troth, 1979; Valverde et al., 1979; Thien et al., 1982; Hartshorn, 1983; Heybrock, 1984; Lott, Bullock & Solís, 1987; Kelly et al, 1988; Rico-Gray et al., 1988; Arriaga & León, 1989; Cuadros, 1990; Saldias, 1991; Dodson & Gentry, 1992; see also summaries for México in Rzedowski, 1991a, b, and for the chaco in Prado, 1993). However, there have been remarkably few attempts to focus on the distinctive floristic composition of dry forests as a whole or on how different dry forest plant communities differ from each other.