EXPERIMENTAL MANIPULATION OF WATER AND NUTRIENT INPUT TO A NORWAY SPRUCE PLANTATION AT KLOSTERHEDE, DENMARK .2. EFFECTS ON TREE GROWTH AND NUTRITION

Water and nutrient supply to forest trees are major factors controllin g tree growth and forest vitality. Therefore, changes in the supply of water and nutrients to the trees may be important contributing reason s to the forest damages observed in Europe. Such changes may be caused by several factors, e.g. air pollution, soil acidification and climat e change. The present study investigates possible effects on tree grow th, growth related parameters and nutrition related to changes in the water and nutrient supply. Water and nutrient supply to the forest soi l was manipulated in three roof covered plots. The treatments consiste d of 1) summer drought, 2) irrigation and 3) combined irrigation and f ertilizer application (fertigation). The results from the roof covered treatment plots were compared to a control plot without roof. Increas ed supply of water during the spring and early summer increased the di ameter growth, whereas application of nutrients in addition to irrigat ion had no additional effect on tree growth. Addition of nutrients inc reased the needle content of P, Mn, Ca and Mg. Extended summer drought for 2 months had no effect on the tree growth or other growth paramet ers, but drought reduced the root development in the upper soil layer. Furthermore, drought induced significant stress symptoms by increasin g the cone shredding substantially.