Anna Maria Jönsson

The effect of burning piles of slash on a Norway spruce clear-cut in southern Sweden was followed for 3 years. The vegetation cover, soil chemistry, soil water at a depth of 30 - 40 cm and runoff water were studied. The burnt plots were without vegetation for several months after burning, while the control plots were almost totally covered by Deschampsia flexuosa and Galium saxatile. The remaining mor horizon of the burnt plots had a pH of 6 compared with pH 4.4 in the control plots. This caused more intense nitrification of the burnt plots that, in turn, caused an acid push with high concentrations of hydrogen ions, nitrate and potassium in the soil water. After 1 year, a cover of D. flexuosa and G. saxatile had also developed on the burnt plots, and the soil water chemistry no longer indicated an elevated leakage of ions. Throughout the study period, no leaching effect was observed in the runoff water. This was explained by nutrient retention of a swamp forest with Betula pubescens on peat soil, surrounding the ditch collecting the runoff water. The increased risk of developing a nutrient imbalance in the next forest generation may strongly outweigh the short-term benefit of reduced competition between tree seedlings and forest floor vegetation, especially if the slash burning is not expected to be of any value for species conservation.