Regeneração natural em uma área de caatinga manejada no município de Upanema no estado do Rio Grande do Norte.

Abstract

Knowing that native forests play important social and economic roles in the Brazilian semiarid region, it is essential to understand the impacts that exploratory activities have upon them and also on the ecosystem in general. Thus, it is essential to know how the vegetation recovers after exploration carried out through sustainable management plan. This work aimed at evaluating the natural regeneration of the arboreal-shrub layer, as well as verifying the accumulation of litterfall in a caatinga area under a forest management system in the town of Upanema, RN. The research was carried out in an area of caatinga vegetation which is under management regime in that town, whose exploration began at annual production unit (APU1) in 2014 and it is currently in the recovery phase. For the study of the adult regenerating component, ten sampling units each with 400m2 were randomly allocated, where all individuals were measured with diameter at breast height (DBH) g 6.0 cm; and floristic composition, horizontal and vertical structures and diameter distribution were also evaluated. As for the evaluation of the juvenile regenerating component, ten sample subunits were used, each with 25m2, in which individuals with DBH < 6.0 cm and height > 0.5 m were measured to evaluate the floristic composition, horizontal structure and the structure of total natural regeneration (TNR). In the study of the litterfall deposition, ten samples were collected with the aid of a hollow mold measuring 0.25 m2, launched at random in each sampling unit. The collection was carried out in two distinct periods of the year (dry and rainy), the collected material was separated into fractions, and the results were compared using the Tukey test at 5%. For the chemical analysis of the litterfall, ten homogeneous samples referring to the sampling units were prepared, which were sent to the laboratory for analysis and determination of the levels of nutrients present in the litterfall. In the study of adult individuals, 488 individuals, 14 species, 13 genera and 6 families were sampled; in the juvenile component there were 179 individuals, 9 species, 8 genera and 3 families. The species that stood out the most on both components were Manihot glaziovi Mull.Arg. blanchetianus Baill, Bauhinia forficata L. The recorded diversity indexes in the area were 1.90 nats.ind-1 Shannon-Weaver (H'), 0.72 Pielou9s evenness index (J) for arboreal and 1.35 nats. ind-1 Shannon-Weaver (H'), 0.61 Pielou evenness (J) for the regenerant. The absolute densities recorded for the area were 1,220 ind.ha-1, 7,160 ind.ha-1, for arboreal and regenerating, respectively. Regarding the litterfall accumulated in the studied area in the two periods evaluated, the highest values were found in the rainy season, with an accumulation of 4,217.32 kg.ha-1, with emphasis on the branches fraction, whereas the dry period the total value was of 2,295.2 kg.ha-1, with emphasis on the leaves fraction. Considering the litterfall nutrients, the sequence was Ca>N>K>Mg>S>P. In general, the results presented by the studied vegetation allow us to say that the area is in a recovery phase, and the exploration regime adopted was one of the determining factors that favors this process, ensuring the continuity of available resources.