3. Doktoritööd
Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7081
Sirvi
Sirvi 3. Doktoritööd Autor "Aun, Kristiina" järgi
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Kirje Short-term effect of felling on carbon fluxes and storages in different Estonian forest ecosystems(Eesti Maaülikool, 2021) Aun, Kristiina; Uri, Veiko; Pumpanen, Jukka (opponent)Boreal forests are large C sinks that play an essential role in the fight with climate changes. However, forest management and especially fellings are one of the important factors affecting stand C accumulation capacity. In the present thesis, the short-term effect of thinning and clear-cutting was studied on the ecosystem C cycling in silver birch and Scots pine stands. On the basis of a compiled C budget, a 6-year-old pine stand acted as a moderate C source (NEP -1.37 t C ha-1yr-1), which was in accordance with the results of eddy-covariance measurements at the same study site (NEE -1.19 t C ha-1yr-1). Since the magnitude of C loss via soil heterotrophic respiration was similar with that in middle-aged and matured stands, then the C source status of the site was attributed mostly to the small biomass of trees and thus to the low annual production of the stand. However, since the annual production of the trees increased in the following years and, assuming a stable annual Rh flux, the ecosystem will become a C sink already during a short period after clear-cut. Therefore, the recovery of the C budget after clear-cut depends strongly on timely and vigorous regeneration. Moderate thinning from below was used in the current study. Thinning did not significantly increase soil heterotrophic respiration in silver birch or Scots pine stands of different ages in the second post-thinning year. As expected, thinning decreased the aboveground C storage of the stand, as well as the production of the tree layer, but all thinned stands still remained their C sink status (NEP 1.5-4.4 t C ha-1 yr-1). Therefore, the use of moderate thinning from below can be recommended the retain a stand as a C neutral ecosystem in the immediate post-thinning period both for silver birch and Scots pine. The recovery of C accumulation rate to the pre-thinning level may occur roughly during the following five years.