INFLUENCES OF SPECIES MIXTURE ON BIOMASS OF NORWAY SPRUCE (Picea abies (L.) Karst.) FORESTS IN THE DUSSELDORF DISTRICT IN GERMANY

Norway spruce (Picea abies (L.) Karst.) is an important tree species for forest plantation in Germany. The planting tree has a very large area especially in Düsseldorf province. And pattern of growing is mixture of with Norway spruce and other tree species. The effect of tree diversity on productivity is poorly understood in subtropical forests in Germany. We investigated the biomass of tree, understory vegetation, coarse roots and fine roots with varying proportions of Norway spruce mixed other tree species at the stands in the same age. With an increase proportion of Norway spruce, biomass of tree and understory biomass increased at first, and then gradually decreased. As expected, biomass of fine roots decreased with soil depth. Stands with 40-60% of Norway spruce had the highest biomass, while stands with <20% of Norway spruce had the least biomass. Stands with <20% Norway spruce had the least understory biomass, while those with 20-40% Masson pine had the least fine root biomass.