| Summary: | The floristic composition and species abundance of the seed bank and the rain of seeds are described and compared in eight seral communities (1-40 years old) related to milpa agriculture in a pine-oak forest area in the Highlands of Chiapas, Mexico. Sticky traps were used to evaluate the rain of seeds throughout their major production period (August 1988-April 1989). That abundance of buried seeds in the milpa field (112 seeds/m2) and in the old-field (92) was significantly lower than in the mid-successional forest (698) and grassland (578) stands. The floristic composition of the seed bank and that of the standing vegetation were not closely related. Pioneer species accounted for >85% of germinated seeds. Seed banks from the edge of different seral stands were richest in species (74 and 65), and included more exclusive species (9-12) than any of the surrounding communities (1-3). The seed rain showed a broad production and dispersal peak in October-February, and most of the trapped seeds were of pioneer species. An increasing forest fragmentation is occurring in the Highlands of Chiapas as a result of the current land use patterns. This deforestation, together with the biological attributes of pioneer species, allow for their accumulation in the soil of the remnant forested stands, and increase the invasion potential of a weedy and exotic flora.
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