SUSTAINABLE PRODUCTION IN SUBTROPICAL HYBRID POPLAR PLANTATIONS

摘要

Little is known of the impact of harvesting intensity on long-term productivity in subtropical forests. We used a simulation model to evaluate whole-tree and stem-only harvesting, rotation length and planting density on hybrid poplar (Populus spp.) stemwood biomass and volume in subtropical China. None of the management scenarios could be sustained without fertilisation with N, the main nutrient considered in the model. Yield decline was a consequence of losses in N capital from leaching and harvest removals and was more severe in whole-tree harvesting versus stem-only harvesting. As nutrient capital was depleted, understorey competition also had increasingly negative impact on stemwood biomass. Total stemwood biomass declined with rotation length. Gains in productivity from delaying harvest were therefore not offset by reduction in harvest frequency. Rotation length and planting density were also important determinants of the differential in total stemwood biomass between whole-tree harvesting and stem-only harvesting. A majority of logs were generated in the 5-20 cm dbh (diameter at breast height) class. Volumes of largediameter (> 20 cm dbh) logs were small on a per-rotation basis but compared favourably to natural stands when multiple harvests were summed over the long term. These poplar plantations will need to be fertilised and managed on a large scale in order to sustain continuous wood flow.