Growth and population structure of the tree species Malouetia tamaquarina (Aubl.) (Apocynaceae) in the central Amazonian floodplain forests and their implication for management

Abstract

The long-term success of forest management depends primarily on the sustainability of timber production. In this study we analyse the population structure, tree age and wood increment of Malouetia tamaquarina (Aubl.) (Apocynaceae) to define a species-specific minimum logging diameter (MLD) and felling cycle by modelling volume growth. Contrary to other timber species in the nutrient-rich white-water floodplains forests (várzea), M. tamaquarina grows in the subcanopy of old-growth várzea forests. The wood of this species is utilized by local inhabitants in the floodplains for handicraft. In 35 plots of 25m×50m we measured diameter at breast height (DBH) and tree height of all trees taller than 150cm height. From 37 individuals with DBH>15cm we sampled two cores by increment borers to determine the wood density, tree age and diameter increment rates. In the management area of a várzea settlement with about 150ha recently harvested trees of M. tamaquarina have been recorded and DBH was measured. The species presents an inverse J-shaped diameter distribution indicating that the species is obviously regenerating in the old-growth forests. Tree-ring analysis indicates a mean age of 74.5 years for a DBH of 22.7cm for a studied population comprising 37 trees with maximum ages of up to 141 years for an individual with a DBH of 45.7cm. The tree species has low annual diameter increment rates (3.16±0.6mm) despite a low wood density (0.36±0.05gcm-3). The volume growth model indicates a MLD of 25cm and a felling cycle of 32.4 years. In the management area 35 trees with a mean DBH of 24cm were recorded, similar to the defined MLD. The abundance of trees above the MLD is 2.7treesha-1, or 405 trees, when extrapolated to the whole management area. Considering a felling cycle of 32.4 years (annual production unit of 4.63ha) this results in total of 12.5 harvestable trees, almost three times less than actually harvested. The actual practice of harvesting M. tamaquarina risks the overexploitation of this slow-growing species. © 2010 Elsevier B.V.