Late-summer soil water content on clear-cut reforestation areas two decades after site preparation in Finnish Lapland

Site preparation has been widely used on reforestation areas in Finnish Lapland due to the high soil moisture and low temperature. The long-term effect of site preparation on soil volumetric water content was studied in ploughed ridges and the untreated intermediate areas of prescribed burning, patch scarification, disk trenching and ploughing plots in eight reforestation experiments 19 years later. Soil water content (SWC) profile measurements were performed with a capacitance probe in the mineral topsoil in the dry late summer of 1993. The mean SWC (2.5–15.0 cm layer) in August in the mineral soil of the untreated intermediate areas varied from 0.13 to 0.20 m^3 m^-3 among the experimental areas, and in ploughed ridges from 0.09 to 0.19 m^3 m^-3. In intermediate areas, no significant differences in SWC were found between the site preparation methods. Soil in and under the ploughed ridges was significantly drier down to a depth of 17.5 cm than the soil at the same depth in the adjacent untreated intermediate areas. SWC was higher on formerly Norway spruce (Picea abies L. Karst.) sites than on Scots pine (Pinus sylvestris L.) sites. The proportion of pine and spruce in the previous tree generation, topography, and soil organic matter content and particle size showed significant correlation with SWC. The basal area of the planted pine saplings significantly affected SWC in the root zone, suggesting that the transpiration and rainfall interception of trees should be taken into account in soil moisture studies on forested sites.