Predação pré-dispersão, chuva de sementes e dinâmica de saída do banco de sementes em florestas jovem e madura da caatinga

Abstract

Forest conversion to agriculture areas modify attributes and ecological processes required for forest regeneration. We aim (i) investigate how the conversion of a mature forest in a abandoned agriculture area affects predispersal seed predation, the seeds size and mass, (ii) verify the annual, seasonal variation and dispersal modes effect in the seed rain, and (iii) investigate the effect of the forest age, season and seed deposition in the dynamics of soil seed bank of woody species. Both forests are located Caruaru, PE, Brazil. Fruits and seeds of the species, Mimosa arenosa and Croton blanchetianus, we collected and measured the seed size and mass, observed the predispersal seed predation. Seed rain was monitored monthly in both forests by seed traps. Output seed bank of the species, M. arenosa, C. blanchetianus and Piptadenia stipulacea were monitored in mesh bags, and placed on the surface and buried at 0-5 cm in the forests. Predispersal seed predation was 18.8% for M. arenosa and 4.3% for C. blanchetianus in the mature forest. In young forest, predispersal seed predation were 16 % and 4.0 %, respectively to M. arenosa and C. blanchetianus. Seed size and mass of the C. blanchetianus differed between mature and young forests. To C. blanchetianus, only the seeds of mature forest showed a significant effect of the size on predispersal seed predation. Seed rain in mature forest had significantly higher density in young forest. Richness and density differed between seasons and higher in the dry season. Richness and seed density also differed between dispersal modes. In the young forest, richness of autochorous, anemochoric and zoochorous species were 25, 21 and 10, while the densities were 159 seeds•m-2•month-1, 16.5 without•m-2•month-1 and without 2.7•m-2•month-1, respectively. The floristic similarity between forests was 0.79, and the year I was 0.75 and was 0.68 in year II. The failure in the output seed bank of M. arenosa suffered significant effect only on the forest age. To C. blanchetianus. Season and seed deposition influenced inn the output seed bank with higher failure in the dry season and seeds buried. Season affected the success in the output seed bank M. arenosa and C. blanchetianus being higher in the rainy season for M. arenosa and in the dry season to C. blanchetianus. Output seed bank of P. stipulacea was not affected. In general, the young forest has features of the initial stages of succession, but the time of abandonment was enough to recovery some ecological process of the populations.