Machinery-induced soil compaction in thinning two pine stands in central Italy

Thinning is a crucial practice in forest management. There is, however, a dearth of studies that focus on the effects of thinning carried out by modern heavy machinery on the physical properties of soil. We studied the consequences of thinning in two pine forests in Central Italy. The “full tree system” (FTS) to convert the whole biomass into chips was applied in both cases, in one case by manual felling in the other using a harvester. Different mass tractors were used to bunch and bring the trees to the landing. We investigated the behaviour of soil in terms of bulk density, total porosity, aggregate stability, penetration and shear resistances, which are good indicators of physical soil quality. Results show that thinning dramatically changed soil properties, depending on the method employed to fell trees and move them along the skid trails or on the whole logging area. In particular, the penetration resistance of soil increased by about 50% and shear resistance by almost 40%, hence confirming that care and surveillance are necessary during thinning to prevent reducing soil quality and, consequently, forest productivity.