Fallow periods on a secondary forest with Platonia insignis Mart. in western Brazilian Amazon

Abstract

Changes in the structure of the vegetation reflect on the biodiversity and dynamics of the ecosystem. The objective of the study was to characterize and compare the structure of fragments of vegetation with the occurrence of Platonia insiginis, in different stages of regeneration, with 6, 10, 25 and 100 years of fallow period in western Brazilian Amazon. The study was conducted in a completely randomized design, with four treatments, consisting of 6, 10, 25 and 100 years of fallow period, and five replications, consisting of demarcated temporary plots for each fallow period, with dimensions of 2 m x 2 m for the regenerating stratum of vegetation and 10 m x 10 m for the adult stratum of vegetation. Phytosociological parameters evaluated were number of individuals and species, total density, total height, stem diameter and Shannon DiversityIndex (H’), Pielou Equability (J) and Jaccard Similarity Index (JSI). The data were subjected to the Analysis of Variance, followed by the Tukey Test (p <0.05) and Principal Component Analysis. There was low species diversity for the sampled areas, with (H’) rates ranging from 0.65 to 2.46 nats ind-1. The vegetation fragments with 100 years of fallow period showed a floristic similarity of 10% with the others, while those of 6 and 10 years of fallow period, reached similarity of 40%. For the regenerating strata only, the number of individuals and total density differed, with the lowest averages, respectively, of 5 and 1,400 individuals ha-1 at 100 years of fallow period. For the adult strata, there was a difference between all parameters corroborating the results obtained in the Principal Component Analysis, at 100 years of fallow period, a lower average was obtained for the number of individuals (7), and higher averages of plant height (22.1 m) and diameter at breast height (36.45 cm). As conclusion, the time required for the complete natural regeneration of secondary vegetation fragments in the Brazilian Amazon is over 100 years