ABSTRACT
In this chapter we discuss the distribution of seasonally dry tropical forests (SDTFs) in Mexico and Central America, emphasize their distinctive characteristics, and provide a summary of floristic and diversity studies of several sites. As a particular case, we analyze floristic affinities and diversity of the Chamela-Cuixmala Biosphere Reserve and adjoining area in Jalisco, Mexico, with respect to different taxonomic levels and life forms. The analysis is based on 1109 species (1064 native), 570 genera (544 native) and 115 families from all the biotic communities in the region from sea level to c.500 m. The native flora analyzed consists of 229 species of trees, 227 species of shrubs, 40 epiphytes, 371 herbs and 197 vines (86 herbaceous and 111 woody). At Chamela, about 41.5% of the species are distributed on the Pacific slope from Sonora and Baja California Sur to Central America, and it appears that this coastal flora is a relatively homogeneous and continuous floristic province. There is an (as yet) imprecisely defined zone of endemism which may encompass the area from Jalisco to the Isthmus of Tehuantepec in Oaxaca. Comparisons are made with diversity and floristic affinities of other Mexican and Central America SDTF sites. Based on the combination of species richness, endemism levels and other factors, we suggest that further conservation efforts might best be focused on the Pacific slope states of Michoacán, Guerrero and Oaxaca.
