Abstract:A growing interest in using forest biomass for bioenergy generation may stimulate intensive harvesting scenarios in Germany. We calculated and compared nutrient exports of conventional stem only (SO), whole tree without needles (WT excl. needles), and whole tree (WT) harvesting in two medium aged Norway spruce (Picea abies L. KARST.) and Scots pine (Pinus sylvestris L.) stands differing in productivity, and related them to soil nutrient pools and fluxes at the study sites. We established allometric biomass functions for each aboveground tree compartment and analyzed their nutrient contents. We analyzed soil nutrient stocks, estimated weathering rates, and obtained deposition and seepage data from nearby Level II stations. WT (excl. needles) and WT treatments cause nutrient losses 1.5 to 3.6 times higher than SO, while the biomass gain is only 1.18 to 1.25 in case of WT (excl. needles) and 1.28 to 1.30 in case of WT in the pine and spruce stand, respectively. Within the investigated 25-year period, WT harvesting would cause exports of N, K + , Ca 2+ , and Mg 2+ of 6.6, 8.8, 5.4, and 0.8 kg·ha −1 in the pine stand and 13.9, 7.0, 10.6, and 1.8 kg·ha −1 in the spruce stand annually. The relative impact of WT and WT (excl. needles) on the nutrient balance is similar in the pine and spruce stands, despite differences in stand productivities, and thus the absolute amount of nutrients removed. In addition to the impact of intensive harvesting, both sites are characterized by high seepage losses of base cations, further impairing the nutrient budget. While intensive biomass extraction causes detrimental effects on many key soil ecological properties, our calculations may serve to implement measures to improve the nutrient balance in forested ecosystems.
In addition to the use of plantation wood for energy, wood from short-rotation plantations can also be used for the production of construction wood and fiberboard. For energy, often wood chips are produced which can be used as fuel in domestic heaters or in combined heat and power plants. Furthermore, wood chips can be processed into second generation fuel (biomass to liquid, cellulasic ethanol). Poplar wood can also be processed into wooden tubes which can be used as supporting construction elements. This process is based on compression followed by deformation while the cell structure remains intact. Such wooden tubes allow an 80% reduction of the material compared to conventional supporting wood elements. Poplar wood can also be used for MDF and HDF production. Tests at the Institut für Holztechnologie Dresden (IHD) have shown that such boards made out of poplar wood meet the DIN EN 622-5 standard with respect to strength and stiffness with very small values for thickness swelling. The formaldehyde emissions from poplar fiber plates are significantly lower compared to similar plates made out of pine wood.
Poplar wood from short-rotation plantations fulfills the technical requirements for the processing of construction elements and MDF, which opens a large economic potential.
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