Effect of conventional and whole-tree clear-cutting on concentrations of some micronutrients in coniferous forest soil and plants

Increasingly intensive and mechanized clear-cutting may deplete the forest ecosystem of essential nutrients. A clear-cut area near Växjö, southern Sweden, was investigated for changes in Mn, Cu and Zn in soil (NH₄NO₃ extractable and HNO₃ soluble) and wavy hair grass (Deschampsia flexuosa) after conventional (CC) and whole-tree clear-cutting (WTC). The soil samples were mostly iron podzols. The area consisted of four clear-cut sites, respectively 2, 4, 6 and 8 years old, and an uncut forest reference stand. Each of the clear-cuts was split in two parts representing WTC and CC sites. Manganese showed the most definite trends after clear-cutting, exhibiting higher extractable concentrations in Oe, Oa and E horizons (4-8 years after clear-cutting) and B horizons (6-8 years after clear-cutting). The increase of exchangeable Mn in the E (2-8 years) and B (4-8 years) horizons was particularly strong. Zn concentrations tended to fluctuate with time. There was a tendency to higher Mn and Zn concentrations in the humus layer especially 2 years after CC-treatment compared with WTC, whereas the opposite trend was apparent for Cu. Mn, Cu and Zn concentrations decreased in Deschampsia flexuosa 2 years after clear-cutting, possibly due to increased soil pH.