Success of mechanical application of Chondrostereum purpureum by two different cutting heads

In young boreal forests, naturally grown hardwoods are usually abundant, restricting the growth of cultivated conifers. Cutting only is inefficient due to quick resprouting of hardwoods, and therefore biological sprout control by using a decay fungus Chondrostereum purpureum (Pers. Ex Fr.) Pouzar has been investigated to provide a better option for young forest management. Due to the high number of hardwood saplings, fully mechanized methods are needed in the biocontrol instead of manual treatments. We investigated the ability of two different cleaning heads to prevent sprouting of naturally grown silver and downy birches (Betula pendula Roth. and B. pubescens Ehrh.) in young Norway spruce (Picea abies (L.) H. Karst.) dominated forests. Hardwood saplings were cut, and their stumps treated with an inoculum containing hyphae of a decay fungus C. purpureum. Three growing seasons after the treatment, birch stump mortality was 80 % and 47 % in the tested cleaning heads. In living stumps, the number of saplings was lower in the fungal treatment than in the cutting only. The diameter and height of stumps, and competition from surrounding saplings and trees regulated the success of the cleaning heads in preventing sprouting. The spreading mechanics of the devices should be developed further to increase their performance.