Comparison of soil inversion and disc trenching: soil disturbance on regeneration sites in northern Sweden 5-10 years after scarification : gentle scarification using the Kicken implement

Sammanfattning

Successful forest regeneration is an important component in modern silviculture, ensuring sustainable production of forest ecosystems services. Mechanical site preparation is a widely used method in Northern Europe to create advantageous conditions for planted seedlings, increasing survival rates and growth, thus contributing to sustainable development of future forests. Yet, existing scarification methods often conflict with other values and stakeholders in the forest, including reindeer grazing, biodiversity, and recreation, due to the extensive impact on soil and vegetation cover. The need to minimize soil disturbance, while maintaining sufficient regeneration quality, has consequently led to a development of new scarification methods targeted at minimizing environmental impact. Soil inversion is often considered a gentle scarification method compared to modern conventional scarification methods due to lower disturbance area by only treating the soil closest to where the seedling is to be planted. Kicken is a gentle scarification implement developed by Bracke Forest AB and uses the concept of soil inversion. Kicken has been used by the forest industry between 2015 and 2020 on sites where gentle scarification methods have been required, primarily on lichen-rich areas used for reindeer grazing. While conventional scarification methods and following soil disturbances have been studied for a long time, no previous long-term assessment on disturbances following soil inversion performed with Kicken has been conducted. The aim of this study is to evaluate soil disturbances levels and vegetation recovery rates on sites treated with soil inversion using Kicken compared to conventional disc trenching. The study was conducted during 2025 by field inventory of regeneration sites in northern Sweden harvested 8-12 years earlier. Total surface area of soil disturbances caused by scarification was measured using a high precision GPS and classified depending on the severity of disturbance. The collected data were analysed and compared between the two treatment groups using statistical methods. The results indicated significantly lower levels of disturbance on sites treated with soil inversion using Kicken compared to conventional disc trenching. Sites treated with soil inversion had on average 92% less exposed mineral soil and 83% less disturbed ground and field vegetation compared with disc trenching on sites harvested 8-12 years ago. The findings indicate lower total disturbance levels on sites treated with soil inversion. Proportion of disturbance level had a significant correlation with time when measuring soil disturbance on sites harvested at different years, indicating a vegetation recovery on sites treated with disc trenching. No significant vegetation recovery could be observed for sites treated with soil inversion. Overall, the results suggest that soil inversion, in this case performed with Kicken can reduce environmental impact, making it particularly suitable on lichen-rich sites where soil disturbance levels should be minimized. Soil inversion may therefore be an important tool for future high precision and low impact regeneration systems.