Bestandesstruktur und leistung der Douglasien-Düngungsversuche Amberg 257, Waldsassen 256 und Burglengenfeld 244 in der oberpfalz

At the beginning of the 70th on sites degraded by former litter raking experiments for testing the effect of different fertilizers on the growth of Douglas fir were established by the chair of forest yield science in cooperation with the chair of soil science. The recording of the stand structure and growth on the experiments Amberg 257, Waldsassen 256 and Burglengenfeld 244 over more than 20 years elucidates that the effect of the fertilizers is superimposed by various calamities in the juvenile stage of the stand. Apart from these disturbances caused mainly by the previous clearcut especially in the initial phase N and Mg fertilizers have a positive effect on the stand growth. Growth of height, basal area and volume can be increased significantly by fertilizers, while needle analyses reflect an only temporarily improvement of the nutrient supply. Top height and yield level show a significant acceleration compared with the control plots in the first years and stay on a raised level also in the following period. From an ecological point of view the establishment of pure Douglas fir stands after clearcut of pine stands on degraded sites should be avoided. More suitable would be a transition to mixed stands suited to the site conditions. Aiming for an economical improvement Douglas fir could be added in such more stable stands in single tree or group mixture. Also in these types of stands a fertilization would be necassary at least to overcome the N and Mg deficiency in the initial phase.