Growth and fructification of a Norway spruce (Picea abies L. Karst) forest ecosystem under changed nutrient and water input

In the mountainous region of a low mountain range (Solling mountains) an ecosystem manipulation experiment with roof constructions underneath the canopy of a 60-year old Norway spruce stand is run since 1991. The responses to artificially prepared, "preindustrial" through fall and to extended summer droughts with intensive rewetting are investigated in two parallel roof experiments and evaluated against a roof control and an ambient control plot. After long terms of drought distinct reactions of the trees were visible in growth. The reactions of height-increment were more distinct than the effects on diameter-increment. Furthermore, the trees of the dominating social classes (Kraft I and II) reacted more on low water-supply than the dominated trees. So it is probable that a long lasting stress by drought effects changes the stand structure, too: the vertical structure of a stand would get more homogeneous and the diversity in the stand structure would decrease. Reduced input of sulphur and nitrogen did not show any distinct growth reactions within the 9-year observation period.