Effects of different forest harvest intensities on the pools of exchangeable cations in coniferous forest soils

Effects of harvest intensity on exchangeable cations (1 M NH4Cl extracts) were examined in four coniferous forest soils in Sweden, 15-16 years after clear-felling. Logging residues were harvested at three intensities, applied experimentally in a randomized block design (n = 4): (i) conventional stem-only harvest, (ii) branches and stems harvested but needles left on the ground and() whole-tree harvesting where all above-stump biomass was harvested, Two of the sites were located in northern Sweden, and the other two were in southern Sweden. In each region one site was occupied by a pure Scots pine stand (Pinus sylvestris L.) and the other by a pure Norway spruce stand (Picea abies (L.) Karst.). Whole-tree harvesting resulted in a lower level of base saturation, especially in the humus layer, Compared with base saturation levels in the stem-only harvest treatment, the reductions were 19%, 16% and 8% at the southern sites with spruce and pine and at the northern spruce site, respectively. At the northern pine site no significant treatment effect was detected. Analyses across all study sites of element pools in the humus and 0-20 cm mineral soil layers indicated that reductions in base saturation generally were associated with depletions of exchangeable pools of K, Ca and Mg. In addition, effective cation exchange capacity per unit area was in general lower after whole-tree harvesting compared with the other treatments, Effects on exchangeable pools of Mn and Zn were similar to those observed for base cations. Exchangeable pools of acidic cations were generally not affected, but at the southern sites pools of acidic cations increased with harvest intensity. No significant differences in soil pH(H2O) were detected between treatments. A relatively high proportion of the Ca left on site in the form of slash was recovered in the soil ca. 15 years after felling, This was not the case for K. Furthermore, the nutrient load recovered in the soil was lower at the southern site with Norway spruce than at the other sites, Apart from these inter-site differences, the results were consistent across all study sites.