Estrututa, regeneração natural e ciclagem de nutrientes em floresta ombrófila densa das terras baixas, na Zona da Mata de Pernambuco

Abstract

The Atlantic Forest, which holds a significant part of Brazil's biological diversity, has been suffering from constant anthropogenic pressures, putting at risk the high wealth of endemic species that make up the Biome. Due to the high degree of disturbance, its conservation today represents one of the greatest challenges. This work aimed to characterize the vegetation as regards structural aspects, natural regeneration and nutrient cycling, in a fragment of Ombrophylous Dense Lowland Forest, in the Zona da Mata of Pernambuco. The arboreal stratum was sampled through 40 plots of 10 m x 25 m, where tree individuals with chest circumference (CAP) ≥ 15 cm, at 1.30 m above ground level, were measured. At the apex of each plot, subplots of 25 m² (5 m x 5 m) were allocated to study the regenerating stratum. The analysis was performed with individuals presenting CAP <15.0 cm and height equal to or greater than 1.0 m. The height classes were pre-determined, where: C1 = height (H) ≥ 1.0 to 2.0 m; C2 = H> 2.0 to 3.0 m; C3 = H> 3.0 m. The nutritional efficiency was evaluated with the ten species of highest absolute density, being evaluated the nutrients N, P, K, Ca and Mg. Leaf biomass was estimated by the Golley equation, which establishes a relationship between DAP and leaf biomass. It was also evaluated the influence of climatic variations on the seasonal contribution of litter and nutrients. The contributions were monitored monthly from June 2014 to May 2015. In order to identify the contribution of the soil to forest nutrition, the soil chemical and physical characterization was carried out, nutrient distribution at different depths and content determination Of plant material. 1.324 individuals were sampled. The family Anacardiaceae had the largest number of individuals and the Fabaceae family had greater wealth. In relation to natural regeneration, 1.197 individuals were sampled and the Fabaceae family was also the one with the greatest wealth. The species Protium heptaphyllum and Thyrsodium spruceanum showed the highest NTNs. The highest leaf biomass estimate was Thyrsodium spruceanum (1.335,78 kg ha-1), followed by the species Protium heptaphyllum (785,24 kg ha-1). Forest species had high demand for N and low for P, and can be established in fertile N and P restricted areas, except Myrcia silvatica and Tapirira guianensis, which can be recommended for soils with low N availability. Was 8.261,15 kg ha- 1 year-1 and the nutrients were 244,93 kg ha-1 year-1. N was the most favored nutrient, being able to cycle, 113,75 kg ha-1 year -1. The litter supply was not influenced by climatic variations. The increase of the depth in the soil profile reduced the nutritional contents in the forest fragment. Forest nutrition occurred in greater proportions in the organic blanket. The soil of the forest fragment basically acted as mechanical support of the species, contributing little to the nutrition, in keeping with the low natural fertility of the tropical soils under the Atlantic Forest.