Using radiocarbon-calibrated dendrochronology to improve tree-cutting cycle estimates for timber management in southern Amazon forests

Abstract

Growth rings are investigated in trees harvested in the second cutting cycle in southern Amazonia and have important implications for dendrochronological studies and for forest management. In the southern Brazilian Amazon, upland moist forests have been managed based on a polycyclic system, which cutting cycle (CC) varies from 25 to 35 years, and the minimum logging diameter (MLD) is 50 cm for all species. Many forests logged during the 1970s are being prepared for the second cycle. However, without growth and yield rates information on the remaining forests as well as for individual species, the principles of sustainable management will be jeopardized. For species with annual growth rings, such information can be obtained using dendrochronological techniques. This study investigated the periodicity of rings in Qualea paraensis and Parkia pendula in a forest that had already experienced one cutting cycle. This information was used to estimate growth and yield rates, and adjusting to equations to estimate individual species MLD and CC. Dendrochronological techniques were combined with radiocarbon analyses to confirm whether rings were annual. Rings of Q. paraensis were confirmed to be annual without radiocarbon analysis. However, P. pendula rings were poorly distinguishable; therefore, delimitation and ring counting were systematically underestimated by 10%. Growth and yield rates of managed forests were favored by logging. The MLD should be 53 cm for Q. paraensis, and 42 cm for P. pendula; and the CC must be 11 and 17 years, respectively. It is concluded that MLD and CC legally defined by the Brazilian laws are not adequate for the studied species; in addition, the use of radiocarbon-calibrated dendrochronology technique is essential to produce robust and unbiased estimates of growth and yield rates.