The effect of stump harvesting on tree growth and the infection of root rot in young Norway spruce stands in hemiboreal Estonia

Abstract Stumpwood as a resource of renewable bioenergy has considerable potential in the Nordic and Baltic countries. So far, however, it has largely been left unutilised in Estonia. This study reports the results of the height growth, needle and twig traits, and Heterobasidion sp. and Armillaria sp. infection in emerging Norway spruce (Picea abies) stands after stump harvesting. After six and eight growing seasons, a significant positive effect of stump harvesting on the height growth of the trees was revealed, compared to control plots with no ground preparation. In one study site stump harvesting was revealed to have a positive effect on the morphologic parameters of twigs and needles, while no differences were noted in the other two sites. The nutrient content of the needles was similar between the treatments across all study sites. Stump harvesting had no effect on the spread of Heterobasidion sp. and Armillaria sp. in the new forest generation. Root infections in young trees with Heterobasidion sp. were detected as early as within two growing seasons from planting. The infection was most severe in the Hepatica site type stand, where 90% of the trees in the previous forest generation had been infected by Heterobasidion sp. In the two other stands studied, where the share of infected trees in the previous generation had been 26% and 16%, Heterobasidion sp. was significantly less widespread. The main causal agent of root rot on all the sampling sites was H. parviporum, but the presence of Armillaria sp. was also remarkable.