Biomass and structure of Norway spruce trees grown in uneven-aged stands in southern Finland

Tree biomass models are increasingly needed for the estimation of carbon storage and for testing and parameterizing process-based growth models, but most biomass models have been estimated using data from even-aged stands. Here we took measurements from individual Norway spruce trees grown in uneven-aged stands in Southern Finland to characterize tree structure and to estimate the biomasses of tree components. Using the data, we tested various structural biomass equations developed for even-aged stands for their suitability to uneven-aged stands. The test trees had longer crowns than usually found in an even-aged Norway spruce stand, ranging from 55 to 85% of total tree height. The average proportion of total biomass in branches and foliage was 13.8 % and 7.0 %, respectively. The average wood density of the test trees was slightly higher than that reported for Norway spruce trees of comparable size. The structural relationships found in trees under even-aged management were applicable to trees growing in uneven-aged stands but required re-parameterization. In particular, the trees had higher branch and stem biomass than trees of same stem and crown dimensions on average in even-aged stands. The relationship of crown ratio and the slenderness index on an uneven-aged stands also differed from those reported in even-aged stands.