Chuva de sementes em área abandonada após cultivo próxima a um fragmento preservado de caatinga em Pernambuco, Brasil

Abstract

The role of preserved fragments of caatinga in the regeneration of an area of abandoned agriculture 15 years ago was investigated. 105 seed traps were placed in the disturbed area, distributed in five transects of 210 m each, perpendicular to a caatinga fragment. Seed traps were placed in strips to each 10m from the fragment. The seed traps consisted of cylindrical polyethylene recipients with 81 cm of circumference (diameter 25 cm) and 30 cm of height, which were placed directly on the ground and done fasten by wood stakes. All seed traps were monitored monthly from August 2008 to June 2009. For species occurring in the fragment and the abandoned area, 10 individuals were selected (when possible) and monitored for the occurrence of seed production and dispersal. Cutting evidences of were recorded and interpreted as regrowth. The test of Kruskal-Wallis was used to analyze the variation in seed richness and density. A simple linear regression was used to evaluate the effect of distance from the fragment in the allochtonous seed rain. Seasonal differences in the seed rain were tested through the Chi-square test. It was recorded a total of 16 families, 32 genus and 56 species; 15 species were woody and 22 were herbaceous. 16 species were identified only at morphospecies level and three at the family level. The species richness in the seed rain varied significantly between strips (H = 132,44; p <0,01) and 140 species of the preserved fragment were not recorded in the seed rain of the disturbed area. The total density of seed rain in the community was 2.270 seeds.m-2 in the year, varying from 300 to 1077 seeds among the 21 distance strips. Seed density of the herbaceous assemblage was 971,2 seed.m-2 and of the assemblage of woody one was of 1.220,2 seed.m-2; 78,2 seed.m-2 species remained unidentified. About 22% of woody individuals established in the abandoned area were regrowth, while in the preserved fragment the number of individuals that established for regrowth was of 4%. Seed rain density differed significantly among seasons ( 2 = 13,63; p <0,01), and was about of twice larger in the dry season (1.511,1 seed.m-2) and moreconcentrated in the early dry season (September, October and November). 28 species (50%) dispersed seeds exclusively in the dry season, being eight (28%) anemochoric, 11 (39%) autochoric and 9 (32%) morphospecies. The results showed that, in semiarid environments, species richness of the disturbed area is not recovered in 15 years, even with the presence of preserved fragments. The regrowth of plants contributes to the regeneration of areas that were cut, but the germination of seeds is an important reproductive strategy in the regeneration of disturbed areas. After 15 years of abandonment, the autochthonous seed rain disables to evaluate the role of the preserved fragment in the seed rain of abandoned area.