Above-ground biomass dynamics after reduced-impact logging in the Eastern Amazon

Changes in above-ground biomass (AGB) of 17 1 ha logged plots of terra firme rain forest in the eastern Amazon (Brazil, Paragominas) weremonitored for four years (2004-2008) after reduced-impact logging. Over the same time period, we also monitored two 0.5 ha plots in adjacent unlogged forest. While AGB in the control plots changed little over the observation period (increased on average 1.4 Mg ha_1), logging resulted in immediate reductions in ABG that averaged 94.5 Mg ha_1 (_42.0), which represented 23% of the 410 Mg ha_1 (_64.9) present just prior to harvesting. Felled trees (dbh > 55 cm) accounted for 73% (_15) of these immediate losses but only 18.9 Mg ha_1 (_8.1) of biomass was removed in the extracted logs. During the first year after logging, the annual AGB balance (annual AGB gain by recruitment and growth _ annual AGB loss by mortality) remained negative (_31.1 Mg ha_1 year_1; _16.7), mainly due to continued high mortality rates of damaged trees. During the following three years (2005-2008), average net AGB accumulation in the logged plots was 2.6 Mg ha_1 year_1 (_4.6). Post-logging biomass recovery was mostly through growth (4.3 _ 1.5 Mg ha_1 year_1 for 2004-2005 and 6.8 _ 0.9 Mg ha_1 year_1 for 2005-2008), particularly of large trees. In contrast, tree recruitment contributed little to the observed increases in AGB (1.1 _ 0.6 Mg ha_1 year_1 for 2004-2005 and 3.1 _ 1.3 Mg ha_1 year_1 for 2005-2008). Plots with the lowest residual basal area after logging generally continued to lose more large trees (dbh _70 cm), and consequently showed the greatest AGB losses and the slowest overall AGB gains. If 100% AGB recovery is desired and the 30-year minimum cutting cycle defined by Brazilian law is adhered to, current logging intensities (6 trees ha_1) need to be reduced by 40-50%. Such a reduction in logging intensity will reduce financial incomes to loggers, but might be compensated for by the payment of environmental services through the proposed REDD (reduced emissions from deforestation and forest degradation) mechanism of the United Nations Framework Convention on Climate Change. (Résumé d'auteur