CONTROL OF BILBERRY VEGETATION BY STEAM TREATMENT - EFFECTS ON SEEDEDSCOTS PINE AND ASSOCIATED MYCORRHIZAL FUNGI

In boreal forest, ground vegetation of bilberry (Vaccinium myrtillus L .) and feather mosses strongly suppress seed regeneration of Scots pin e (Pinus sylvestris L.). We investigated a site preparation technique by steam treatment to control bilberry and moss vegetation after clear cutting. Sowing experiments were performed between 1993 and 1995 with Scots pine in four treatments: (1) untreated vegetation, (2) activate d carbon added to the soil surface of otherwise intact ground vegetati on, (3) steam treated vegetation, and (4) activated carbon added to th e soil surface of steam treated vegetation. Activated carbon was added to adsorb possible phenolic compounds released from bilberry leaves a nd litter. Steam killed ground vegetation effectively and recolonisati on of vascular plants and mosses was slow. Scots pine seedling establi shment was improved by steam treatment especially when activated carbo n was added to the soil surface. We interpret that activated carbon ad sorbed and reduced the levels of phenolics from bilberry litter and hu mus, which otherwise may inhibit seed germination. Dry weight of four year old seedlings was three times higher in steam treated plots than in untreated plots. Seedling nutrient content was also strongly improv ed by steam treatment. We interpret the increased growth of seedlings in steam treated plots mainly as an effect of reduced resource competi tion from ground vegetation. Irrespective of treatment, almost all fin e roots were colonised by ectomycorrhizal fungi. Using PCR-based molec ular methods we were able to identify 28 taxa forming mycorrhiza on th e seedlings. Steam treatment did not affect species richness and abund ance of ectomycorrhizal inocculum. We conclude that steam treatment ha s the potential to be an efficient and environmentally acceptable meth od to reduce negative influence of bilberry vegetation on Scots pine s eedling establishment and early growth. (C) 1998 Elsevier Science B.V.