VEGETATION CONTROL BY STEAM TREATMENT IN BOREAL FORESTS - A COMPARISON WITH BURNING AND SOIL SCARIFICATION

The Vaccinium myrtillus L. - feather moss vegetation community immobil izes nutrients in surface organic layers and suppresses growth of coni ferous seedlings in northern boreal forests. On a site dominated by th is type of vegetation, a new site preparation technique, involving ste am treatment to kill ground vegetation, was tested and compared with c onventional site preparation techniques such as soil scarification and burning. Steam treatment was as efficient as burning and soil scarifi cation in reducing competing vegetation. After 4 years, Scots pine (Pi nus sylvestris L.) seedlings planted in the burned and scarified treat ments had lower growth, needle dry weight, and nitrogen contents compa red with seedlings in sites treated with steam. Soil microflora recove red quickly after steaming, suggesting that steaming does not directly cause long-term soil sterilization. We interpret the superior growth of P. sylvestris seedlings in steamed plots as being due to both stron gly reduced resource competition and enhanced release of nutrients in the remaining humus. We conclude that steam treatment has the potentia l to be an efficient and environmentally acceptable method to reduce t he negative influences that ericaceous ground vegetation has on the gr owth of planted coniferous seedlings.