Measuring ecological impacts from logging in natural forests of the eastern Amazonia as a tool to assess forest degradation
Sound forest management practices have been seen as an interesting strategy to ally forest conservation and rural economic development in Amazônia. However, the implementation of Reduced Impact Logging (RIL) techniques in the field has been incipient, while most of the Amazonian timber production is generated through predatory and illegal logging. Despite several improvements in remote sensing technologies focused on improved monitoring of illegal logging, a consolidated methodology to assess the quality in the implementation of management practices in the field – and therefore the level of degradation caused by harvesting – is needed. We present here a method based on a study conducted in 1996 at a forest site in Paragominas, Eastern Amazônia. The original objective of this study (Holmes et al. 2002) was to compare the costs and benefits of Conventional Logging (CL) with Reduced Impact Logging (RIL) under an economic perspective. This study created a method to assess ecological impacts caused by logging, which has been intensively replicated in the last 14 years in the field activities of the Instituto Floresta Tropical (IFT). The method is based on two assessments: (i) Damage to the residual trees in the forest stand; (ii) Proportion of ground area disturbed during harvesting by heavy machines. The first assessment is conducted through a simple evaluation of future-crop trees (DBH > 35 cm) in relation to damages in their crown and their boles which, combined, generate a classification of the general health status of the tree. The distribution of remaining trees in these health status classes characterizes the overall impact from harvesting over future crop trees. The second, the assessment of ground area disturbed was executed by measuring the area of roads, log decks and skid trails (width and length). In addition, the method includes a measurement of merchantable timber waste incurred during each type of logging. This included: (a) Timber felled and not found by skidding crew or left in the forest because poor felling caused logs to split and lose merchantability; (b) Timber left on the log deck; (c) Timber wasted because cutting stumps were too high or due to poor bucking of felled logs. Such relatively simple assessments proved to be efficient in measuring forest degradation caused by timber harvesting and revealed dramatic differences in the ecological damages caused by RIL and conventional logging.