Restoration of biodiversity: Seed, rain, and recruitment of woody species in a Mexican secondary dry forest

The elimination of perturbation may be enough to increase biodiversity in low diversity secondary forests dominated by few pioneer species. In January 2006, eight sites of 0.25 ha were excluded from cattle ranching in Sierra de Huautla, Morelos to evaluate seed rain and recruitment of woody species in established secondary vegetation. At all sites, all woody vegetation with DBH > 5 cm was tagged and identified, seed rain was evaluated monthly and recruitment of woody species was measured once. We found 33 woody species (14 families) in the secondary forest. After 6 months of seed rain we recorded 152 morphospecies and 17184 seeds, an average of 38 seeds /m²/month but only 19 % of those identified correspond to woody species while 80 % were seeds from herbs.  Only 9 % of the seeds recorded (11 species) belonged to woody trees found in mature forest, while 10 % belonged to woody trees usually found in perturbed sites (8 species). Recruitment of woody species was very poor compared to existing vegetation: 169 seedlings (13 species) were recorded, from which 92 % belonged to three pioneer species: Mimosa benthamii (Fabaceae, 63 adults), 81 recruits; Acacia cochliacantha (Fabaceae, 151 adults), 51 recruits and Ipomea pauciflora (Convolvulaceae, 99 adults), 23 recruits. Woody seed rain was composed of an even proportion of pioneers and non-pioneer seeds, however, only pioneers are recruiting individuals. Our results suggest that plantation of non-pioneer species that experience strong dispersal and establishment limitation is necessary to increase biodiversity in these sites.