Vegetation control by steam treatment in boreal forests: a comparison with burning and soil scarification

The Vaccinium myrtillus L. n feather moss vegetation community immobilizes nutrients in surface organic layers and suppresses growth of coniferous seedlings in northern boreal forests. On a site dominated by this type of vegetation, a new site preparation technique, involving steam treatment to kill ground vegetation, was tested and compared with conventional site preparation techniques such as soil scarification and burning. Steam treatment was as efficient as burning and soil scarification in reducing competing vegetation. After 4 years, Scots pine (Pinus sylvestris L.) seedlings planted in the burned and scarified treatments had lower growth, needle dry weight, and nitrogen contents compared with seedlings in sites treated with steam. Soil microflora recovered 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 strongly reduced resource competition and enhanced release of nutrients in the remaining humus. We conclude that steam treatment has the potential to be an efficient and environmentally acceptable method to reduce the negative influences that ericaceous ground vegetation has on the growth of planted coniferous seedlings. Resume : Liassociation vOgOtale composOe de Vaccinium myrtillus L. et diune mousse hypnacOe immobilise les OlOments nutritifs dans les horizons organiques de surface et retarde la croissance des semis de conifres dans les forŒts borOales nordiques. Une nouvelle mOthode de prOparation de terrain, impliquant un traitement ‡ la vapeur conAu pour tuer la vOgOtation du parterre, a OtO mise ‡ liessai et comparOe ‡ des mOthodes conventionnelles de prOparation de terrain comme le scarifiage et le brslage sur un site dominO par ce type de vOgOtation. Le traitement ‡ la vapeur a OtO aussi efficace que le brslage ou le scarifiage pour rOduire la vOgOtation compOtitrice. Aprs 4 ans, la croissance, la masse anhydre des aiguilles et le contenu en azote des semis de Pinus sylvestris L. plantOs dans les parcelles brslOes ou scarifiOes Otaient plus faibles comparativement aux semis plantOs sur les stations traitOes ‡ la vapeur. La microflore du sol a rOcupOrO rapidement aprs le traitement ‡ la vapeur, ce qui suggre que ce traitement nientraOne pas directement une stOrilisation ‡ long terme du sol. Les auteurs attribuent la croissance supOrieure des semis de P. sylvestris dans les parcelles traitOes ‡ la vapeur ‡ lieffet conjuguO diune forte rOduction de la compOtition pour les ressources et diune libOration accrue des OlOments nutritifs de lihumus rOsiduel. Ils concluent que le traitement ‡ la vapeur pourrait siavOrer une mOthode efficace et acceptable du point de vue environnemental pour rOduire les effets nOgatifs de la vOgOtation diOricacOes au sol sur la croissance des plants de conifres. (Traduit par la ROdaction)