Biomass allocation and carbon stock in Douglas fir and Norway spruce at the tree and stand level

The effect of changing tree species composition in favor of a greater representation of Douglas fir at the expense of Norway spruce on the carbon pool of Central European forests has not yet been investigated. Here, we compare the allocation of aboveground biomass and carbon stock in Douglas fir and spruce at the tree and stand level. At the tree level, Douglas fir accumulated, on average, 16.9% more aboveground biomass than Norway spruce. A greater amount of biomass was allocated mainly in the wood and bark of Douglas fir stem. For these biomass compartments, the difference between Douglas fir and Norway spruce was 21.1% and 60.3%, respectively. Spruce allocated more biomass in the crown, where the difference was 25.6% compared to Douglas fir. In needle biomass, Norway spruce exceeded Douglas fir by 84%. At the stand level, the analysis of model stands revealed that pure Norway spruce stands accumulated more carbon in the high and medium quality sites. As the site quality decreased, so did the differences in the amount of stored carbon. The higher carbon sink in Norway spruce stands was also confirmed in the analysis of real Norway spruce and Douglas fir stands. The difference in the carbon stock of young, medium-aged, and mature stands was 11.5%, 14.8%, and 1%, respectively. The positive balance in favor of spruce is mainly due to significantly higher numbers of trees per ha in Norway spruce stands. A positive effect of a greater representation of Douglas fir on the carbon budget of forest stands was not confirmed.