Banco de sementes no solo em uma área de caatinga em regeneração, Núcleo de Desertificação de Irauçuba, Ceará.

Abstract

The objective of this study is to gather knowledge about the attributes of a seed bank at soil level and to verify which of these attributes reflect the best regeneration of the caatinga in areas of desertification. In order to do that, we investigated the seed bank at the end of the dry season in a area of caatinga suffering the process of degradation/desertification, at the municipality of Irauçuba, Ceará. We analysed the attributes of density, composition, diversity and richness of species as well as germination dynamics. The collections were realized in three areas, at Formigueiro, Cacimba Salgada I and Cacimba Salgada II farms. In each area, we sampled a seed bank at soil level in the experimental portion (fallow) and at the continuous use portion (control). Each portion of each area was divided in sixteen portions of 10 x 10 m, from which were drawn five portions for the study of the seed bank at soil level. In the center of each one of the five portions of 100 m2, a soil sample of 0,25 m2 was removed. The density and the composition of the seed bank at the soil level were analysed using the plantule outgrowth in greenhouse. The bank was composed primarily by therophytes. The densities found were 592, 1804, 2080 seeds/m2 for the experimental portions 1, 2 and 3, respectively, and 680, 1288 and 1408 seeds/m2 for the control portions 1, 2 and 3, respectively. Regarding the richness parameter, we found equal values for both the experimental and control portions (8 and 2 for areas 1 and 2, respectively); area 3 presented greater richness in the fallow portion (15 and 10 for the control and experimental portions, respectively). The equability values of the experimental portions were equal to 0,751, 0,041 and 0,740 for areas 1,2 and 3 respectively and of 0,613, 0,054 and 0,603 for areas 1,2 and 3 of the control portions. Regarding diversity, the values for the experimental portions 1, 2 and 3 were 1,562, 0,028 and 2,004, respectively, and 1274, 0,038 and 1,388 for the control portions 1,2 and 3, respectively, which reveals a major diversity for the areas of fallow, with exception of area 2. The raising diversity and density demonstrate the occurrence of regeneration of the herbaceous component in the fallow areas.