Effect of mechanical site preparation on soil quality in former Norway spruce sites

Mechanical site preparation (MSP) enhances Scots pine (Pinus sylvestris L.) plantation establishment on cutover pine sites in northern Fennoscandia, but long-term impacts of MSP on soil quality on cutover Norway spruce (Picea abies (L.) Karst.) sites have remained obscure. We measured soil dielectric permittivity (ε) as dependent on soil water content (θv), soil electrical conductivity (σa) and soil solution electrical conductivity (σw) at 14 former spruce sites, 8–23 years post-MSP in Finnish Lapland. The sites were mechanically prepared with Marttiini-plough that had created cross-contour disturbance tracks with following microsites: trench, tilt and untreated control between the tracks. Soil water content in trenches or untreated control was not lower as compared to that of spruce forest reference. Tilts were lower in soil θv, but this feature, however, appeared to vanish within 23 years. Soil electrical conductivity of all microsites was much lower as compared to spruce forest reference, and significant degradation of soil quality was observed such that untreated control-σa > tilt-σa > trench-σa. The soil σw was consistently lowest in trenches, evidently due to snowmelt induced leaching cycles. MSP treatments were unable to contribute to permanent changes in soil water regimes and site-specific soil water regimes appeared to be attributable to spatial variability of soil physical properties rather than MSP.