Site impact after motor-manual and mechanised thinning in Mediterranean pine plantations

The study determined the site impacts of motor-manual and fully mechanised whole tree harvesting, as applied in the thinning of young pine plantations on the Tuscan coastline. The thinning was applied with selection criteria, removing between 36 and 39% of the tree number. The frequency of tree wounding was 1.5 and 5%, respectively for the mechanised and the motor-manual treatment. Wounds inflicted by the mechanised system were also four times smaller than those inflicted by the motor-manual system. The superior performance of the mechanised system was ascribed to its better capacity for handling cut trees. Soil bulk density increased by 3% and 6% after motor-manual and mechanised harvesting, respectively. The increase was small but significant, whereas the difference between treatments was not significant. Machine traffic resulted in a significant increase of CO2 concentration in the soil air, which was 0.4% in the undisturbed control plots and 0.8% in the machine tracks. No significant difference was found between the treatments. The CO2 concentration in the machine tracks was very near to the 1% critical threshold, beyond which biological activity is so constrained that soil recovery may be significantly delayed. When repeated entries are necessary, it is best to avoid creating new tracks by restricting traffic to designated permanent tracks. Properly applied mechanised harvesting does not cause heavier soil impacts than traditional motor-manual harvesting, but it results in a much lower stand damage. Foresters may support the introduction of mechanised harvesting, to the advantage of productivity, economics and work safety.