Degradation of forests through logging and fire in the eastern Brazilian Amazon

Abstract

The status of tropical forests in the Amazon basin is often expressed in terms of deforestation extent. However, in the eastern Brazilian Amazon logging and ground fires degrade forest structure and create land cover types that are intermediate between intact and cleared forest. The objective of this study was to provide a basis for understanding the implications of forest degradation by comparing the impacts of varying intensities of logging and fire on forest structure and composition. Field inventories in forests whose impacts ranged from none to logged and heavily burned were conducted in 14, 10 m×500 m plots located on 10 properties in the region of Paragominas, Pará, Brazil. Live aboveground biomass of intact forest was estimated at 309 t ha −1. Following moderate intensity logging (35 m 3 ha −1 removed), this value was decreased by 20%, but a 48% reduction was observed following high intensity logging (69 m 3 ha −1 removed). Light burning of moderately logged forest resulted in a total biomass reduction equal to that of high intensity logging whereas moderately logged and heavily burned forest had 83% less live biomass than intact forest. Recovery of pre-degradation biomass and forest structure is likely to be impeded by abundant lianas and the high incidence of crown and stem damage in the residual stands. Although burning killed the majority of large diameter woody vines, increase in the abundance of lianas <1 cm diameter, (mean stem density 4100 ha −1 in lightly burned stands and 9355 ha −1 in heavily burned), more than compensated for these losses in terms of total liana density. In addition, increased amounts of coarse woody debris and greatly reduced canopy cover in both heavily logged and heavily burned forests have increased the risk of future fires that could further degraded these forests. As more and more logging frontiers in the eastern Brazilian Amazon mature it is likely that repeated logging of previously logged stands will become more common. This combined with the increased flammability of previously burned stands is likely to result in the spread of forest degradation unless incentives can be developed to encourage the use of low impact logging techniques and the development of cost effective fire prevention methods.