Precommercial thinning stumps´susceptibility to Heterobasidion spp
a comparison between high and low Norway spruce and birch stumps
Each year, Heterobasidion spp. is a major cause of economic losses to forestry in the northernhemisphere, including Sweden. New results indicate that pre?commercial thinnings could be at riskfor Heterobasidion spp. infections. Since no wood usually is used from pre?commercial thinnings,there would not be any timber losses from leaving high stumps instead of low stumps when carryingout this measure. It could therefore be of a great interest if the stump height, of both Norway spruce(Picea abies (L.) Karst.) and birch (Betula spp.), affects the susceptibility to Heterobasidion spp. aftera pre?commercial thinning is performed.The objective of this study was to investigate if there were any differences in infection frequencyfrom airborne Heterobasidion spp. spores depending on whether the stump height is high (1 m) orlow (15 cm) in pre?commercial thinnings in the southern Sweden. The efficacy of stump treatment byPlebiopsis gigantea (Fr.) Jül. and the infection frequency of birch were also investigated for the twostump heights in five different sites.There was a significant difference in infection frequency between treated spruce, untreated spruceand birch when samples from both high and low stumps were included.The efficacy is a measure of the reduced mean relative infected area of the infections related to acontrol. High untreated spruce did not show a difference in efficacy compare to low untreatedspruce, nor did treated spruce and birch.The infection frequency of birch stumps was significant higher on high stumps (17.3 %) and hencethey were more susceptible to Heterobasidion spp. than low (12.2 %).No significant effect of the susceptibility depending on the stump height was observed for untreatedspruce nor treated spruce.Other reasons than risk of infection could be a reason to create high treaded spruce stumps. Onereason could be the more ergonomic treatment height compared to perform stump treatment onlow height.A five year long?term research study was established with the objective to investigate if a knownHeterobasidion spp. infection spreads into surrounding trees or if it dies out in inoculated high andlow spruce stumps.It is possible that the stump height is of importance for the spreading of Heterobasidion spp.infections in the long?run, which is the purpose of the long?term study to find out.