Densidade e composição do banco de sementes do solo em uma floresta de restinga após perturbação por fogo : implicações para a restauração

Abstract

The soil seed bank is one of the most important sources of natural regeneration in tropical forest ecosystems altered by natural or anthropogenic events. Therefore, the analysis of the influence of spatial and temporal variations on the floristic composition, species richness and seed density found in this system allows inferences about the regenerative potential of a given area. Thus, this study evaluated the dynamics of the soil seed bank after the occurrence of a surface fire that hit part of the Restinga forest inserted in the Private Natural Heritage Reserve Nossa Senhora do Outeiro de Maracaípe, located in Ipojuca, Pernambuco, Brazil. The fire persisted for two days and took place in February 2013, the time they were made the first collections both in burned forest physiognomy and in the forest physiognomy not burned. In each stretch of forest (burned and not burned) were collected 50 soil samples using a collector 20 x 20 cm, 5 cm deep over five transects 90 m. The sample comprised the dry and rainy periods corresponding to two consecutive years. The collected soil samples were stored in polyethylene bags, labeled and transported to the greenhouse, where they were packed in polystyrene trays, which are monitored and watered daily for a period of six months. The determination of the density of seeds in the seminal soil bank was performed by the method seedling emergence. The influence of fire and seasonal periods on the richness of species and seed density, between areas and between years, was checked by the GLM and to see if there were differences in mean values of richness and density, the Tukey test was applied to posteriori (5%). To compare the floristic composition of the seed bank between areas and seasons was carried out NMDS and the similarity between the samples was verified by the ANOSIM test. After two years of research, there were 1.521 individuals in the samples from the area not burned, distributed in 32 families, 41 genera and 61 species. In the area burned down the overall density of 1.133 individuals belonging to 20 families, 28 genera and 38 species. The floristic composition between areas was significantly different, but the opposite was found for seed density. In the area not burned there was seasonal variation in species composition, but between years the floristic composition was similar. In the burned area there was no seasonal variation in species composition, but between years, the floristic composition was different. Considering the years of study and evaluated the different environmental conditions, the average species richness was higher in the not burned during dry season I. There was a predominance of herbaceous species on both banks, particularly the herbaceous Paepalanthus bifidus (Schrad. Ex Schult.), and among the tree, stood out the pioneer Cecropia polystachya Trécul, these species represented 47% of the total density germinated seeds. Tree species were most significant in the forest not burned. However, the richness of woody species found in burned forest increased over the period since the fire. With respect to the dispersion and regeneration groups syndromes, there was a predominance of zoochoric syndrome (67.5%) and early succession species (57.1%). The disturbance was of low intensity and hit the surface vegetation, partially removing the vegetation. In addition, the proximity of vegetation preserved surrounding the burned forest area probably favored seed dispersal, leading to an increase in the seed bank in the soil found after a small-scale disturbance. Thus, the data obtained indicate that despite the Restinga forest have been disturbed by fire, the soil seed bank found in the different evaluated environmental conditions, continues to represent an important source of seeds for natural regeneration of this ecosystem because it contains species which has a potentially positive impact on the real flora found in the forest.