Fitossociologia e acúmulo de serapilheira em uma área de caatinga submetida a diferentes sistemas silviculturais.

Abstract

This study aimed to evaluate the effect of silvicultural systems on adult and regenerating components of Caatinga vegetation, as well as investigating the influences of silvicultural systems and the alternative uses of soil on accumulated litter stock and your relation with nutrient support to soil, in two areas. The first area is in Seridó Ecological Station (SES) and the second is on Pedro Candido Farm (PCF), in the Serra Negra do Norte-RN, Brazil. In the adult component, in each area, 16 subplots of 400 m2 were delimited and individuals with a base circumference > 6 cm were measured. Floristic composition, horizontal and vertical structures and diametric distribution were studied. The density data, diversity and volumetric production were submitted to the comparison of averages, by applying the Tukey Test at 5% significance. In the regenerating stratum, in each area 16 subplots of 25m2 were used. Individuals with a base circumference ≤ 6 cm and a height > 0.5 m were measured. The floristic composition, horizontal structure, the structure of natural regeneration (RNR), and the type of regeneration origin were studied. The density and diversity data were compared by Tukey test at 5% significance. The accumulated litter was collected in the rainy and dry seasons with the aid of a frame of 0.25 m2 , being a sample for each plots of the silvicultural systems. Samples were separated into fractions: leaves+reproductive structure, branches and miscellaneous, which were compared by Tukey Test at 5% of significance. For the chemical analysis of litter, homogeneous samples were prepared for each silvicultural system, being composed of the mixture of the crushed material referring to the four repetitions of each fraction in each area. In the adult component, lower anthropism in SES favored the development of a more balanced community in terms of structure. In PCF, a greater number of pioneer species shows that the two types of use propitiated different responses to silvicultural systems. In both areas and in all silvicultural systems, prevailing individuals in diameter at breast height < 3.9 cm and total height < 5.27 m. The selective cut provided the highest values of diversity and volumetric production, and favored the development of a more balanced diametric structure. In the regenerating component, the lower anthropism in the SES provided the regeneration of a richer community with lower dominance. In the SES, in terms of RNR, it was found that the Croton blanchetianus, Poincianella pyramidalis and Aspidosperma pyrifolium were, respectively, the most important. In PCF, the most important were, respectively, Croton blanchetianus, Aspidosperma pyrifolium and Mimosa tenuiflora. There was no significant effect of silvicultural systems on absolute density and diversity. Relative to litter, there was no significant effect of silvicultural systems on the evaluated fractions, but there was significant difference between the areas in relation to the branches. The upper accumulation on the PCF, did not result in a better efficiency of nutrient deposition. The selective cut presented the best efficiency of nutrient input to the soil.