Physical recovery of forest soil after compaction by heavy machines, revealed by penetration resistance over multiple decades

Soil compaction , which results from the skidding of heavy machines used in forest operations, can seriously damage forest productivity. Indeed, it alters soil structure, disturbs its physical features and consequently affects gas exchange and biological activities. The impact of compaction on soil health has been widely studied, but less is known about the recovery of soil properties over time. In this study, soil compaction was examined by measuring soil penetration resistance. In order to detect the soil recovery on a multi-decadal scale, a space-for-time substitution approach was implemented. Two soil types from the Compiègne forest (Northern France) were investigated (i.e. Luvisol and Podzol). Heavy machine trails of compaction were selected and dated using LIDAR outcomes (Light Detection and Ranging), management documents and aerial photographs. A chronosequence for each soil type was created: 0, 10, 24 and 45 years for the Luvisol and 0, 2, 8, 13 and 23 years for the Podzol. A total of 432 penetration resistance profiles of 30 cm depth were performed in the ruts, as compacted soil, and beside the ruts in undisturbed soils, as control. Penetration resistance was significantly higher in compacted soils in comparison to control soils; it was also higher in the Luvisol than in the Podzol. A linear model with second-order polynomial relationship was used to test the interactions between the penetration resistance, the depth, the situation (compacted versus undisturbed) and the age of compaction. Variance partitioning showed that penetration resistance was mainly controlled by depth, followed by compaction and compaction age, and finally by soil type. The model showed a recovery trend over time as a decrease of the penetration resistance, and a recovery dynamic from the surface toward the deeper layers. The predicted duration of the complete recovery was about 54 and 70 years for the Luvisol and Podzol, respectively. This work also infers that sandy neutral soils could recover in less than 20 years, favored by soil biological activities.