Soil Compaction and Recovery after Mechanized Final Felling of Italian Coastal Pine Plantations

This study gauged the severity and permanence of soil compaction associated with mechanized clear felling of umbrella pine plantations. We tested three treatments: not harvested, harvested one year earlier and harvested six years earlier. Each treatment was replicated eight times in randomly distributed 0.5 ha plots, on the same soil type. Soil compaction was assessed by gauging soil bulk density, penetration resistance, deflection under impact and CO2 concentration. These parameters were measured with steel rings, penetrometer, deflectometer and soil air analyzer, respectively. Measurements were conducted on 8 clear cut blocks per treatment, which had been randomly distributed over the same forest, with identical soil and stand type. One year after clear fell, bulk density increased by 9%, penetration resistance by 50% and deflection by 60%. Porosity decreased by 10%, which entailed a parallel 30% increase of both soil moisture content and CO2 concentration in the soil air. Six years after clear fell, there was no sign of recovery for bulk density, deflection and moisture content. On the contrary, penetration resistance was significantly reduced, and CO2 concentration was back to the values recorded in plots that had not been harvested.