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Sirvi Autor "Metslaid, Marek (advisor)" järgi

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  • Pisipilt
    Kirje
    Evaluation of forest management in the context of carbon fluxes: Eddy-Covariance method
    (Eesti Maaülikool, 2020) Rebane, Sille; Jõgiste, Kalev (advisor); Metslaid, Marek (advisor); Nilsson, Urban (opponent)
    Boreal forest, being a widely distributed vegetation type as well being a substantial part of the global carbon (C) cycle, must be addressed to understand the consequences of climate change. Forest ecosystems are part of the biosphere as a whole and have a role in maintaining global equilibrium. Also, forest ecosystems have the ability to regulate Earth´s climate and energy fluxes. The forests, including boreal and hemiboreal forests, can absorb CO2 from the atmosphere and store carbon in biomass. This kind of ecosystem study is conducted by the widely used eddy covariance (EC) method. It is the most adequate way to measure net ecosystem exchange (NEE) between ground and atmosphere. EC is a direct micrometeorological measurement method for identifying C-fluxes in forest ecosystems. Clear-cutting changes the forest ecosystem C-balance. It is assumed that immediately after a clearcut, a huge amount of C is released, which make a forest stand act as a C-source. The time necessary for forest ecosystem recovery after clear-cutting also depends on the choice of regeneration method. Natural regeneration usually takes more time than artificial regeneration by planting or sowing and the proper regeneration method may shorten the recovery period. In Estonia, clear-cutting is the common forest management practice followed by planting to establish the new forest generation. Planting may speed up revegetation that increases C sequestration. Thus, proper forest management practices provide important strategies to mitigate global climate change. After clear-cutting, a 5-year-old mixed stand acted as C-neutral forest ecosystem during the measurement period (May to August). In the 6- and 8-year-old study stands, the ecosystem showed already C-sink status during the measurement period (June to September). Literature review showed that after clear-cutting, recovery to C-sink status could take 10 years and in some cases even 20 years. Forest recovery after wildfire may take up to 50 years and most likely even more. Measurements after insect outbreaks and windstorm disturbance detected recovery after 3 to 6 years; however there were few such studies and more research is needed for further comparisons.
  • Pisipilt
    Kirje
    Post-fire recovery dynamics of hemiboreal Scots pine forest ecosystems
    (Estonian University of Life Sciences, 2024) Orumaa, Argo; Metslaid, Marek (advisor); Institute of Forestry and Engineering; Brazaitis, Gediminas (opponent)
    ABSTRACT. Hemiboreal forests are influenced by several natural disturbances. Forest fires are one of the most severe disturbances that can affect the entire forest ecosystem: stand structure and composition, understorey vegetation, soil nutrient quantities and properties, and soil biota. In this thesis, the chronosequence method was used to study the impact of fire on above- and below-ground components of hemiboreal Scots pine forest stands. The fire chronosequence consisted of areas burned in the years 2008, 1997, 1982, 1951, 1940, and 1837. Soil respiration was affected by time since fire and it was lowest in the most recently burned area. CH4 measurements showed that post-fire soil was CH4 sink in all the areas. The highest uptake of CH4 was measured in the most recently burned area and the lowest uptake was recorded in the oldest area, but there were no statistically significant differences between the areas. For N2O fluxes, the soil acted as both a sink and a source in post-fire areas, but there were no statistically significant differences between the areas. There were considerable compositional differences in the vascular plant and bryophyte assemblages between recently burned (burned in 2008, 1997 and 1982) and older burned (burned in 1951, 1940 and 1837) stands. The cover of the vascular plants and bryophytes layer increased with time since fire, while the trends for species richness and diversity along the post-fire chronosequence were less clear. For soil fungi, hemiboreal forests are typically dominated by Basidiomycota, but in the post-fire stands studied in this thesis, Ascomycota was dominating. Along the fire chronosequence, soil fungal communities were primarily dominated by fungi for which a functional group could not be determined, followed by soil saprotrophs, EcM fungi, and root endophytes.