Soil water-retention characteristics of Scots pine and Norway spruce forest sites in Finnish Lapland

Abstract

Scots pine and Norway spruce forests, which differ from each other ecologically and economically, dominate in Finnish Lapland. The need to investigate the soil properties of these forests has increased due to the problems found in forest reforestation. The present paper examines soil water-retention characteristics (WRC), hydraulic conductivity ( K), texture and organic matter content (OMC) in 10 Scots pine ( Pinus sylvestris L.) and 10 Norway spruce ( Picea abies L. Karst.) dominated forest sites in Finnish Lapland (North Finland). In general, the studied soil properties were comparable to those reported earlier for till soils in Lapland and Fennoscandia. However, according to semivariogram analysis, the properties showed spatial dependence within sites that was most commonly below 60 m. Moreover, the properties differed significantly between the pine and spruce sites ( P<0.05). The most significant differences were in the water content (WC, vol.%) at −5 and −10 kPa matric potentials ( ψ) (i.e. near field capacity) and in the sum of the OMC and fine particle fraction (<0.06 mm). Compared with the spruce sites, the pine sites had thinner genetic soil horizons and lower OMC, less fine particles and a lower WRC. The air-filled porosity (AFP) and saturated K were higher on the pine sites. The most significant vertical differences in AFP and WRC between the pine and spruce soils were found at depths of 3 and 50 cm below the organic horizon. The proportion of pine (of basal area) in the tree stands showed a significant positive correlation with AFP at −5 and −10 kPa ψ. The mean WC content and AFP at −10 kPa ψ were <30 and >20 vol.%, respectively, at about 80% of the sampling points on the pine sites, while on the spruce sites the values of >30 and <20% occurred at a corresponding number of points. The results showed that pine and spruce sites in Lapland differ significantly in their soil physical properties. The sites where pine is naturally dominant tend to have a lower soil WC especially near field capacity (c. −10 kPa ψ) than spruce sites, which suggests that Scots pine requires drier soil for optimal growth and regeneration than Norway spruce.