Composição florística do banco de sementes e da regeneração natural em área de caatinga em processo de recuperação.

Abstract

Floristic composition of the seed bank and natural regeneration in a caatinga area undergoing recovery. The Caatinga Biome is a mosaic of herbs, shrubs and trees most of them adapted to the hot and dry climate. In addition to the climate, human activities may degrade the soil and affect seed bank composition, natural regeneration and plant growth. This study determined the seed bank flora and the diametric classification of adult and regenerating trees established in a recovering caatinga site, located at the NUPEARIDO Experimental Station, Patos-PB, Brazil, by planting pioneer (Mimosa tenuiflora and Cnidoscolus quercifolius) trees in a first moment approximately two years ago, and secondary (Handroanthus impetiginosus and Amburana cearenses) trees. Seed bank composition relied on a 50 sample-set collected and kept in a screened protected environment at the UFCG/CSTR seedling nursery facilities for data collection regarding seed germination and identification of plant species, family and habit of growth. Shannon-Weaver (H’) and Pielou Uniformity (e’) indexes were calculated to estimate species diversity and richness. Adult and young trees had the circumference at breast height and basal diameter measured, respectively, for distribution in diametric classes. Additional data on annual precipitation, soil moisture, and survival of adult secondary planted trees were collected. Seed bank showed to be rich in herbs, especially those from Poaceae, Convolvulaceae and Fabaceae families. Adult M. tenuiflora and C. quercifolius predominated in the diametric Class II. Mimosa tenuilfora young trees were numerous in Class I, while most of C. quercifolius were in Classes II, III and IV. Mortality of secondary planted trees showed to be high, possibly due to factors such as the irregular rain distribution and the low soil moisture.