Geological controls on conifer distributions and their implications for forest management in Finnish Lapland

Abstract

Soil water and nutrient regimes of naturally established old-growth conifer stands and those of intensively managed Norway spruce [Picea abies (L.) Karst.] sites were assessed over a range of lithological provinces in Finnish Lapland. Soil dielectric permittivity (ϵ), as a measure of soil water content (θ v) and soil electrical conductivity (σ a), as a measure of soil solute content, were species specific, such that high soil θ v>0.27 cm3cm−3 (ϵ>15) constitutes an edaphic constraint for Scots pine (Pinus sylvestris L.) and low soil solute content (σ a<0.5 mS m−1) is constraining for Norway spruce. The spatial pattern of the soil θ v was temporally stabile, such that intraseasonal and interseasonal soil θ v was significantly higher in silty tills of spruce stands compared to sandy tills of pine stands. Scots pine was the only conifer on tills derived from felsic rocks of Hetta granite (HG) and Lapland granulite (LG). Norway spruce dominated on tills derived from the mafic rocks of Lapland greenstone belt (LGB), but tills of LG and HG constitute a dispersal barrier for spruce. Mechanical site preparation (MSP) with ploughing (Marttiini) was not able to amend soil θ v to meet site requirements of Scots pine at former spruce sites. MSP resulted in significant reduction in soil nutrient content such that untreated control σ a>tilt/shoulder σ a>trench σ a. The results imply that MSP treatments through which cross-contour tracks are created pose a risk to the sustainability of soil quality in Lapland.