The natural recovery of disturbed soil, plant cover and trees after clear-cutting in the boreal forests, Russia

This study aims to determine the impact of forest harvesting machinery on the temporarily moist soil of spruce forests (Picea abies Karst.) during the summer. For research purposes, we investigated 23 sites of the boreal forest in the European North of Russia (Arkhangelsk region) where logging operations had been carried out using harvesters and forwarders (CTL, cut-to-length harvesting). In the 15 years after logging, the sites were monitored for changes in physical soil properties and the depth/width of ruts and vegetation. In freshly cut areas, the depth of the ruts was linked to the amount of logging residue that had been used to strengthen skidding trails. After 15 years, the ruts were smooth but had not disappeared entirely. The average depth of the ruts decreased from 36 cm to 18 cm during the period under review. At a depth of 0-10 cm, the soil bulk density of the section between the control area and the wheel track increased by 19-27% within the first two years. At a depth of 10-20 cm, the soil bulk density only increased by 16-17% within the two-year period. After 15 years, the soil bulk density had decreased to the extent that there were no signs of heavy machinery movement. The natural restoration of vegetation in the ruts was affected by the presence of stagnant water in the initial post-logging period. Ruderal species and species with broad ecological amplitude to environmental factors grew over the skid trails. 15 years after logging, this overgrowth had stabilised, with the biodiversity level in the control area approaching its pre-logging state. Primarily, the renewal of the cutting areas occurred through species such as birch (Betula pendula Roth.) and aspen (Populus tremula L.). The highest amount of undergrowth (more than 30,000 ha(-1)) was detected 6-8 years after logging. This then decreases in areas that were cut down earlier. There are environmental consequences of clearcutting (using the CTL system) on temporarily moist soil. To prevent the formation of deep ruts, it is recommended to leave 15-20 kg m(-2) of felling residue.