Forestry-drained peatlands occupy approximately 15 million ha in boreal and temperate zones. In Finland, they represent almost one-fourth of the total forest area. They are subjected to the same harvesting operations as upland forests. Although the soil deformation caused by timber harvesting is well documented in upland forests, the knowledge on the soil disturbance induced by the harvesting machinery on peat soils is still lacking. To address this, we collected soil samples from six peatland sites that were thinned using a harvester–forwarder combination. Peat samples were taken from the trails formed by the machinery and outside the trails to a depth of 10 cm. To assess the recovery of soil properties after the disturbance, we sampled sites along a chronosequence with respect to time since harvesting. Soil deformation under the machinery appeared to increase the bulk density and field capacity of peat and decrease its total porosity; however, disturbed plots and control plots started to resemble each other in their soil properties within 15 years. The results imply that peat soil is sensitive to disturbance but has a high recovery potential.

In the boreal region, peatland forests are a significant resource of timber. Under pressure from a growing bioeconomy and climate change, timber harvesting is increasingly occurring over unfrozen soils. This is likely to cause disturbance in the soil biogeochemistry. We studied the impact of machinery-induced soil disturbance on the vegetation, microbes, and soil biogeochemistry of drained boreal peatland forests caused by machinery traffic during thinning operations. To assess potential recovery, we sampled six sites that ranged in time since thinning from a few months to 15 years. Soil disturbance directly decreased moss biomass and led to an increase in sedge cover and a decrease in root production. Moreover, soil CO2 production potential, and soil CO2 and CH4 concentrations were greater in recently disturbed areas than in the control areas. In contrast, CO2 and CH4 emissions, microbial biomass and structure, and the decomposition rate of cellulose appeared to be uncoupled and did not show signs of impact. While the impacted properties varied in their rate of recovery, they all fully recovered within 15 years covered by our chronosequence study. Conclusively, drained boreal peatlands appeared to have high biological resilience to soil disturbance caused by forest machinery during thinning operations.

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