Impact of mechanical site preparation on soil properties at clear-cut Norway spruce sites on mafic rocks of the Lapland Greenstone Belt

Ploughing disturbance and inversion of soil sequences result in erosion and leaching of suspended solids and nutrients in northern boreal forests. Here, we assessed microsite soil physical-chemical properties at two cut-off spruce (Picea abies L. Karst.) sites 12, 14 and 16 years and microsite morphology with LiDAR DEMs 25 years after ploughings. The sites, one treated with (Marttiini) shoulder ploughing (SP) and the other with tilt ploughing (TP), contained the following microsites: trench, tilt (TP) or shoulder (SP), and untreated soil between the disturbance tracks. Using the classification and regression tree (CART), 90% of the microsites were correctly explained with apparent soil electrical conductivity (a.) and dielectric permittivity (DP). CART of soil chemistry explained 74.7% of microsites with the most important variates being C, Mg, Na, Mn, Ca, Ba, Al, Fe and N. Concentration of the elements in trench were significantly (p = 0) lower than in untreated microsites such that decrease for Al (49%), Ca (46%), S (51%), C (67%), and N (57%) at TP-site, as well as AI (31%), Ca (34%), K (30%), Mg (56%), Na (32%), P (22%), S (32%) and N (37%) at SP-site were observed, respectively. Ploughings had negative impact on the soil properties, such that the artificial regeneration with spruce had failed. Micromorphology still remains after 25 years and losses in soil nutrient supply will continue during consecutive snowmelt events implying that soil inversion does not sustain soil quality in Lapland.