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3. Doktoritööd

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7081

Sirvi

Sirvi 3. Doktoritööd Autor "Bergström, Dan (opponent)" järgi

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    Kirje
    Management of second-generation hybrid aspen stands and its environmental impact
    (Estonian University of Life Sciences, 2025) Hepner, Heiki; Lutter, Reimo (advisor); Tullus, Hardi (advisor); Tullus, Arvo (advisor); Institute of Forestry and Rural Engineering; Bergström, Dan (opponent)
    ABSTRACT. In short-rotation forestry in Northern Europe hybrid aspen is used as a preferred tree species. It is important to understand the effects of thinning on second-generation hybrid aspen stand growth, biomass production, soil fertility, nutrient accumulation in the above-ground parts of trees, carbon balance, and economic profitability. After the first growing season, the average stand density was 94,000 trees/ha. After five growing seasons, trees in the control area had produced an average of 31.4 t/ha of dry biomass, resulting in an average annual production of 6.3 t/ha. On the corridor and cross-corridor thinning areas, the total biomass after five years was lower compared to the control area, but when considering also the biomass harvested with thinning, there was no significant difference. The intensive pre-commercial thinning using the single-tree selection method can cause slower stand growth and further self-thinning. After five years, the change in carbon stock was positive in the control and corridor treatment areas, while it remained neutral in the cross-corridor treatment area. Carbon stock increased in the aboveground biomass but decreased in the soil. Soil fertility indicators showed varied changes. With very short coppice cycles, nutrients accumulated in biomass make up less than 10% of the total stock, except for potassium. In the case of a very short coppice cycle, the harvest should be done when the trees are dormant. When growing logs and pulpwood, the very intensive first thinning should be avoided. With low expected economic return (discount rate of 1%), the single-tree method proved most effective. Under moderate expectations (5% discount rate), the corridor method yielded the best outcome. For high and very high return expectations (10% or 20% discount rates), the focus should be only on energy wood. In summary, hybrid aspen regenerates vegetatively very well, and provides flexible management options and economic profit in Estonian conditions.