Oberirdische holzige Biomasse in Kiefern-/Buchen- und Eichen-/Buchen-Mischbeständen

Data on the amount of woody biomass within a forest ecosystem are necessary prerequisites for many economical and ecological questions. Because detailed measurements are laborious and thus can not be carried out on a broad scale, equations are used to estimate tree and stand biomass from tree dimensions. However, this approach suffers from a number of uncertainties involved in the equations. The data base on the various tree species, regions and age classes from which the functions are derived is not uniform. Most of these investigations were carried out in homogenous, even-aged forests and it is questionable whether the derived equations are valid as well for mixed and more structured stands. Bark biomass has not often been considered as a separate compartment because its share of the total biomass is relatively small. Nonetheless, it is particularly important if nutrient contents are to be investigated as well. The present paper compliments available analyses by investigating two middle aged stands dominated by an upper tier of Sessile oak and Scots pine, respectively, and which contain a well developed understorey of European beech. The study focuses on biomass estimation but shall serve as basis for further investigations of nutrient balances in dependence on management intensity. 15 oaks (with diameter at breast height between 10 and 33 cm), 15 pines (10-30 cm) and 20 beeches (4-16 cm) were harvested and analyzed with respect to the biomass of the major aboveground woody compartments, including bark. The biomass of stem and branch parts with a diameter larger than 7 cm at the smaller end (DHmr) were determined separately for heart- and sapwood from volume measures and wood density measures. Bark biomass (DHr) of this fraction was quantified from bark samples taken along the shaft axis (volume and dry weight were measured as well). Other woody crown fractions (NDH) were estimated used samples that were dried, weighted, and scaled to the whole crown by the branch basal area. Results generally confirm literature findings about the relation between basal area at 1.3 m height and total aboveground woody biomass (BM). Non-linear regression curves give r²-values between 0.97 and 0.99 with no apparent bias. The fraction of DHmr and DHr to BM was found to be constant over the range of investigated trees. In conclusion, the derived equations are assumed to be suitable for estimation of woody biomass in mixed stands and could be applied in conjunction with nutrient analyses to investigate the impact of different harvesting strategies on nutrient cycling.