Caracterização florística, estrutura e da dinâmica de regeneração de espécies nativas em um povoamento comercial de Eucalyptus grandis em Itatinga, SP

Abstract

The objectives of this study were to analyze a floristic composition, the structure, some aspects of the dynamics of regeneration of native species in understory of commercial stands of Eucalyptus spp and to study the impact that some silvicultural practices (thinning and clear cut) have on regeneration. For this purpose, 17 samples (0.68 ha total sample area) were located in a stand of Eucalyptus grandis (Stand 48), on the São José do Bromado Farm, geographical coordinates 23°13’30’’S and 48°34’07’’W, municipal of Itatinga, Sao Paulo. In the evaluation of the composition and structure of the regeneration, done 30 months after the clear cut of the first rotation of Eucalyptus grandis, all of the individual trees up to 1.5m of height were tagged and identified. The study of the temporal evolution of regeneration was done in 2 evaluations, 30 and 45 months after the clear cut of the stand. The same method of analysis was used, being that the individual trees measured previously and not found in the second evaluation were considered dead. After the second evaluation the samples were divided into three treatments: Treatment 1- control (sample area of 0.2ha), of which the trees were maintained, Treatment 2 (sample area of 0.24ha), of which 50% thinning was done, and Treatment 3 (sample area of 0.24ha), of which clear cut was done. After the implementation of the treatments (46 months after the exploration), two evaluations were accomplished. The first at 54 months and the second at 61 months, after the exploration of the first rotation of the stand. One thousand nine hundred trees (104 species and 38 families) were sampled in the first evaluation. The largest floristic family verified was Myrtaceae followed by Asteraceae, Fabaceae and Solanaceae, the family which presented the largest density of individuals. Whereas the species with the greatest relative density were Solanum variabile and Matayba elaeagnoides. Among the individual samples, 76.66% were of the families that present a pattern of aggregate spatial distribution. In evaluating the dynamics of regeneration, it was found that the recruitment of new individuals in understory of eucalyptus during the period of 30-45 months after the commercial exploration was focused on the groups of initial secondary species, late secondary and typical species of understory. The mortality was concentrated in the group of pioneer species and non-classified species, respectively. The index period to the Shannon diversity (H’), presented growth of 3.48 to 3.573, and eqüability (J’), growth of 0.751 to 0.762, showing to have gained in relation to the diversity of species of the area. The study of the impact that different silvicultural practices have on regeneration, treatment 1- presented the least incidence of mortality and the greatest incidence of species during the analysis period. The practices of thinning and clear cut caused a great impact on treatments 2 and 3, improving the incidence of mortality and decreasing the incidence of new individuals of regeneration. Treatment 2 was the only one to present gains in diversity (H’) in all of the evaluations.