3. Doktoritööd
Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7081
Sirvi
Sirvi 3. Doktoritööd Autor "Brazaitis, Gediminas (opponent)" järgi
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Kirje Assessment of climate effects on Scots pine (Pinus sylvestris L.) growth in Estonia(Eesti Maaülikool, 2017) Metslaid, Sandra; Kiviste, Andres; Kangur, Ahto; Brazaitis, Gediminas (opponent)The doctoral thesis focuses on the influence of long-term local weather variation on Scots pine growth on a temporal and spatial scale. Dendrochronological methods were used to determine the most influential climatic factors affecting Scots pine radial growth. Since the site index is commonly used in forest growth and yield models as a proxy to describe site productivity, possible climate change impacts on long-term tree height growth were analysed using the site index comparison approach. The findings of a case study in South Estonia were based on the annual growth of three retrospectively reconstructed generations growing in different periods of time which showed that pine trees established after 1960 had elevated growth rates compared to stands established decades earlier. Over a longer time span, this resulted in different cumulative growth patterns and a higher site index. Meteorological data evidenced that thermal climatic conditions for the youngest trees established around 1970 were significantly warmer compared to the time period when the oldest trees were growing, which positively contributed to accelerated growth. Tree-ring analysis from more than 900 Scots pine trees revealed that radial growth response to annual weather fluctuations varied in Estonia on the spatial scale and depended on local climatic circumstances as well as on ecological site conditions. According to the results of the studies conducted within the framework of this thesis, late winter/early spring temperatures and meteorological water availability in late summer prior to the ring formation season are the main climatic factors driving Scots pine growth in Estonia. The thesis also elaborated a basal area increment model for individual trees, which incorporates the effect of thinning and climate related influences. The results of this thesis demonstrate how important it is to account temporal and spatial climatic variability on tree growth, even in such a small country like Estonia, especially in research when making comparisons between different sub-regions or referring to past tree growth.Kirje Post-fire recovery dynamics of hemiboreal Scots pine forest ecosystems(Estonian University of Life Sciences, 2024) Orumaa, Argo; Metslaid, Marek; 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.