Abstract
The conservation of tropical forests is recognized as one of the most important challenges for forestry, ecology and politics. Besides strict protection, the sustainable management of natural forests should be enhanced as a key part of the foundation for the maintenance of tropical rain forest ecosystems. Due to methodological reasons it has been complicated to attain reliable growth data to plan sustainable felling cycles and rotation periods. Tree ring analyses enable the estimation of growth rates over the entire life span of trees and their age as well as giving hints from forest dynamics in previous centuries. For tree ring analysis, stem disk samples were taken from three important commercial tree species (Cariniana micrantha, Caryocar villosum and Manilkara huberi) in the upland (terra firme) forests of the Precious Woods Amazon logging company near Itacoatiara, Brazil. Based on radiocarbon estimates of individual growth zones, the annual nature of tree rings was proven for the three species. Tree rings were measured and the results used together with height estimates to model diameter, height and volume growth. The age of the eldest tree, a C. micrantha, was 585 yrs with 165 cm in diameter. The species’ diameter increments range from 0.20±0.12 cm yr-1 to 0.29±0.08 cm yr-1. At first sight, this is considerably lower than increments reported from other Amazonian or African timber species. Considering the respective wood density there is no significant difference in growth performance of dominant timber species across continents. The interpretation of lifetime tree ring curves indicate differences in shadow tolerance among species, the persistence of individuals in the understory for up to 150 years and natural stand dynamics without major disturbances. Management criteria should be adapted for the measured growth rates as they differed considerably from the Brazilian standards fixed by laws (felling cycle of 25–35 years and a common minimum logging diameter of 50 cm). Felling cycles should be increased to 32–51 years and minimum logging diameters to 63–123 cm depending on the species.
Highlights
The Amazonian lowland rainforest is the largest connected rainforest in the world. It is a hotspot for biodiversity comprising some 16.000 tree species [1] among many other taxa playing a key role in the global carbon cycle and acting as a huge carbon storage base and sink [2, 3]
The growth zones of Caryocar are defined by an uneven vessel distribution with periodic zones of large fiber bands that are free of vessels and parenchyma (Fig 2)
Tree ring formation in tropical trees has been neglected for long time due to an assumed lack of seasonal climate and growth patterns [17]
Summary
The Amazonian lowland rainforest is the largest connected rainforest in the world It is a hotspot for biodiversity comprising some 16.000 tree species [1] among many other taxa playing a key role in the global carbon cycle and acting as a huge carbon storage base and sink [2, 3]. This unique ecosystem is endangered by an increasing demand on agricultural products in the Amazon region, an increasing population [4] and unsustainable or illegal logging [5]. The concepts of sustainable forest management strongly contrasts this widely used practice which aims to encourage the long-term use of natural resources that promise an a way to protect tropical forest ecosystems [9]
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