Cambios en la estructura y composición de la vegetación relacionados con los a？os de abandono de tierras agropecuarias en la selva baja caducifolia espinosa de la reserva de Dzilam, Yucatán

the dry forests in the northern yucatan peninsula are highly important not only for science but also for the conservation of biodiversity because of their unique biogeographical and ecological characteristics. the combination of arid climate, stony soil and relative isolation from other biogeographical regions, has resulted in their sheltering an important proportion of the peninsula's endemic taxa. nevertheless, this region suffers from such human pressures as cattle ranches and the exploitation of limestone banks. this scenario makes it necessary to describe the ecological changes on the land once it has been abandoned after being used for agriculture, because there is no pristine forest in yucatan. we compared the structure and composition of trees and shrubs on abandoned agricultural land of different ages. all sites were derived from tropical dry forest, a vegetation type which contains several endangered species. the changes in composition and relative abundance of the subfamilies belonging to the leguminosae (papilonoideae, mimosoideae and caesalpinoideae) were also reported, since this family was the most abundant at the study site. average tree height and density and shrub richness showed larger changes with increasing number of years without management (anova, p< 0.05). younger plots (1-5 years and currently in use) were more similar among themselves than to older sites (more than five and more than ten years). the leguminosae were the richest family in species in all the plots and one of the most abundant, possibly indicating a history of intense use. agriculture tends to deplete nitrogen from the soil, which gives a competitive advantage to legumes. papilonoideae were the most abundant in older sites (more than five and more than ten years), whereas mimosoideae dominated recently abandoned sites (five years or less) and those currently in use. metopium brownei, bursera simaruba and plumeria rubra were the most abundant species in the oldest site. the fir