Seed rain in an agricultural landscape in Los Tuxtlas, Mexico

Background/Question/Methods: Deforestation due to agricultural activities leads to degradation of rain forests; this generates a heterogeneous matrix of forest fragments, pasture lands, cultivated lands and secondary vegetation. In pastures, seeds that arrive by dispersal events are the only sources of individuals for regeneration. We aimed to describe the seed rain in the primary forest, secondary forest and pastures close to a Reserve of tropical rain forest of the Mexican National University at Los Tuxtlas, Veracruz, Mexico. One hundred and twenty seed traps (1m²) were placed in primary and secondary forest and in pastures. Traps were emptied monthly from December 2006 to December 2007. Results/Conclusions:

We identified 140 species from 57 families. In 12 months, we recorded 80,799 seeds from which 89 % were from woody species. Thirty five percent of the woody species recorded in the seed rain were pioneers, from which 24.68 % were species dispersed by animals. More than 40 % of the seeds of woody species recorded in the seed rain belonged to late-successionals, from these seeds, 32.47 % of the seeds species were dispersed by animals. The density of species (F _{(2, 24)} = 21.65, P < 0.0001) and seeds (F _{(2, 24)} = 68, P < 0.000001) was significantly different for each life form (woody or non-woody) in each habitat. In the primary and secondary forest density of woody species and seeds were higher than that of non- woody species while in pastures the density of species and seeds from non-woody species was higher. For all life forms, the density of species (F _{(22, 264)} = 4.83, P < 0.000001) and seeds (F _{(22, 264)} = 4.34, P < 0.000001) was significantly different by month for each habitat: primary forest and pastures showed the highest density of species and seeds in May while in secondary forest the highest densities were recorded in September. The highest density of seeds and woody species dispersed in the primary forest and to pasture was in the rainy season. Meanwhile, in the secondary forest, were seeds are primarily dispersed by wind, the highest densities were found in the dry season. Very few seeds of woody species are dispersed into pastures by animals or wind; most seeds that arrive into pastures are from grasses and herbs.  Thereby, the composition of species of the primary forest may not be reached by natural regeneration alone in open pastures > 500 m from seed sources.