The effect of harvest intensity on long-term calcium dynamics in soil and soil solution at three coniferous sites in Sweden

Removal of logging residues may lead to soil and surface water acidification by lowering the amount of buffering base cations. Long-term treatment differences in soil exchangeable calcium pools (down to 20 cm) and soil solution calcium concentrations at 50 cm soil depth were examined at three coniferous sites in Sweden following conventional and whole-tree harvesting in 1974-1976. Results from the statistical analysis (p <0.05) showed that soil water concentrations of calcium were 17 mu eq 1(-1) (or 40%) lower in whole-tree harvested plots compared with conventional harvested plots, 27-30 years after harvest. The main treatment differences had largely disappeared 32-35 years after harvest although site specific treatment differences (Delta WTH-CH: -24 mu eq 1(-1)) were still measurable at the well-buffered site in northern Sweden. These results are in agreement with soil data showing that previously found treatment differences in calcium pools had diminished in the forest floor but remained in deeper soil layers (-0.29, -0.37 and -0.24 kmol(c) ha(-1) in the 5-10, 10-15 and 15-20 cm soil layer, respectively). The presence of an interaction effect in the 10-15 cm soil layer indicates, however, that the treatment response on calcium pools is much less at the southern sites. These results indicate that the effect of WTH on soil and soil solution concentrations is temporary but site specific. Contrary to common beliefs, the greatest soil and soil water effect was observed at the well-buffered site where the loss of calcium during WTH is less likely to lead to acidification effects. The treatment effects on soil solution at the more acidic sites in southern Sweden were much smaller and probably not large enough to fully counterbalance the general recovery from acidification during the study period.