Logging scenarios for sustainable timber harvesting in the tropical rain forests of central Guyana

For sustainable forest management, information is required on the long-term consequences of current logging practises for tree species composition and future timber yields. Yet, little is known about these long-term effects of logging on species composition and forest recovery. We used a simulation model of forest dynamics to study the effects of logging with different harvest intensities on stem densities of different functional groups and on remaining commercial volumes for forests in central Guyana. We also assessed the time needed for these stem densities and volumes to return to base-line values obtained from simulations without logging. In addition we compared 18 alternative logging scenarios for sustainable timber harvesting. These scenarios consisted of 18 combinations of maximum allowable harvest intensity (4, 8 or 12 trees ha-1), minimum felling diameter (35 or 60 cm) and felling cycles (25, 40 or 60 years). After logging once, the commercial volumes at all harvest intensities returned to base-line values. At the highest harvest intensities, however, the two classes of commercially most valuable species needed approximately 100 years to recover their commercial volumes. This is substantially longer than the currently advised felling cycle of 60 years. As a consequence, for all evaluated poly- cyclic scenarios the commercial volume declined over simulation time. The highest average annual yields were obtained with felling cycles of 25 years, but at high harvest intensities these felling cycles led to rapid depletion of the commercial volume. After logging once the abundances of all functional groups returned at all harvest intensities to values similar to that of the base-line simulations without logging. Generally, return times increased with increasing harvest intensities. The longest return times were found for the small pioneers, small climax species and medium sized climax species that at highest harvest intensities need between 113 and 161 years to return to base-line values. After simulated logging the stem density of small pioneer increased rapidly. Over simulation time these pioneers thus need a long time to decrease again to base- line abundances. The climax groups on the other hand needed a long time to recover from the loss of stems that were killed or harvested during logging. The effects of logging on functional group composition were, however, found to be rather small. The results of this study show that it is possible manage the forests in central Guyana in a way that results in relatively small changes in functional composition and still achieves more or less sustained yields. The results of this study can be used to rank the scenarios based on criteria for productivity and sustainability. Forest managers and decision makers can use these results as input for multiple criteria analysis to objectively decide on what would be the most desirable logging practices.