Effect of fertilization of a secondary spruce stand in the Kobernausserwald with shoot blight symptoms

Many secondary spruce forests in central Upper Austria are affected with Si rococcus conigenus, a fungus causing shoot blight. Affected trees show prog ressive crown deterioration and often stands need to be harvested long befo re they reach the prescribed rotation age. In an experiment in the Kobernau Berwald we investigated whether an improvement of the nutritional status he lps to preserve these stands. Several plots in a 60 year old spruce forest were treated with combinations of organic fertilizers, magnesium rich carbo nate fertilizers and classical NPK fertilizers. We assessed the defoliation of the canopies, the intensity of Sirococcus shoot blight, the chemical so il condition and the nutrient content of needles. Seven years after the fer tilization the soil pH was only slightly raised. The magnesium pool was enh anced where magnesium fertilizers have been applied. The response of nutrie nt content in needles was quite variable. The greatest improvements were ac hieved with magnesium carbonate fertilizers. The intensity of Sirococcus sh oot blight was reduced. The improvement of the nutritional status seems to have modified several resistance mechanisms of trees and have promoted reco very. Therefore stand fertilization is a valuable tool to stabilize stands that are affected with S. conigenus in order to facilitate the consecutive stand conversion by means of silvicultural methods.