Trajetórias de crescimento de árvores de Goupia glabra - Aubl em uma floresta secundária na Amazônia Central

Abstract

Secondary forests, or forests in regeneration, have become dominant forest typologies in tropical regions. In the Legal Amazon, it is estimated that 20% of the deforested areas are covered by secondary forests. In addition to their contribution to forest restoration efforts, when well managed, secondary forests can be important sources of forest products. Studies conducted in tropical regions have shown the ability of these forests to recover both species richness and wood productivity. However, this potential is still poorly understood for the secondary forests of central Amazonia. Goupia glabra is one of the species of great economic importance in the Amazon region and occurs abundantly in secondary forests. In the present study, the general objective was to evaluate the wood properties and growth trajectory over the years of G. glabra trees in a secondary forest site. The study was conducted in an area of secondary forest approximately 37 years old and 35 hectares long, located on the Experimental Farm of the Federal University of Amazonas (FAEXP/UFAM). For this purpose, the diameter at breast height (DBH) of the G. glabra trees recorded in 10 1-hectare plots was measured and classified according to the degree of canopy exposure to sunlight. DBH disks were collected from thirty four trees, distributed in different size classes and positions in the vertical layer of the forest were collected. The X-ray densitometry imaging technique was used to more accurately identify the boundaries of the growth rings and to obtain the microdensity profiles. From the measurement of the width of the rings with the software WinDENDRO©, using images generated by the equipment Faxitron MX20-DC12O, the indicators of mean annual increment (MAI) and current increment (CAI) of the trees were calculated. Estimates of tree height, biomass and volume were obtained from modeling. The average values of wood microdensity ranged between 0.93 and 0.87 g cm - ³ in the pith-bark direction. A strong variation was observed in the radial growth of the trees. The growth rates of G. glabra trees were significantly influenced by the degree of canopy exposure. Trees belonging to the high-exposure class had higher growth rates in average annual growth in DAP (0.51 cm), cumulative cross-sectional area (0.0380 m 2 ) and increase in estimated cross-sectional area (0.0008 m² year -1 ), as well as in values of productivity, MAI-volume (0.00636 m³ year - ¹) and MAI-biomass (5.028 kg year - ¹). Trees of the low-exposure class had MAI–DBH values of 0.19 cm, cumulative cross sectional area of 0.0086 m², increase in estimated cross-sectional area of 0.0004 m² and productivity of 0.0022 m³ year -1 for MAI-volume and 1.720 kg year -1 for biomass. Despite the observed growth differences, the trees did not reach maximum MAI values in the three exposure classes. Regarding basic wood density, there was no difference between the exposure classes of the crowns. The results obtained for trees of G. glabra indicate that the species remains with great growth potential in the secondary forest site studied and has significant intraspecific variation in productivity. This information may contribute to the definition of management feasibility and implementation of future silvicultural interventions in this stand, which may serve as a reference for conservation and management actions in other secondary forest sites in the Amazon.