Sirvi Autor "Kangur, Ahto (advisor)" 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 (advisor); Kangur, Ahto (advisor); 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 Assessment of ecosystem memory in hemiboreal forests: structural legacies and size distribution in Järvselja old-growth forest(Estonian University of Life Sciences, 2026) Nigul, Kristi; Kangur, Ahto (advisor); Frelich, Lee E. (advisor); Institute of Forestry and Rural Engineering; Klopčič, Matija (opponent)ABSTRACT. The study area is located in the Järvselja Training and Experimental Forest Centre, Estonia. Forest protection in the Järvselja old-growth forest was established in 1924, when the area was excluded from all management activities and left to develop naturally. The findings from Studies I–IV provide both quantitative and qualitative insights into the composition of the Järvselja old-growth forest and assess the influence of historical legacies on ecosystem memory. The study analysed data from more than 10,000 trees. Norway spruce and linden were the most prevalent tree species in the Järvselja old-growth forest. Over the past century, the number of dominant tree species has increased slightly. The standing volume and proportional contribution of birch, common aspen, and Scots pine have decreased, whereas those of linden and black alder have increased. The data suggest that deciduous species now occur more frequently in smaller diameter classes than in the past. In addition, gap dynamics were evident, reflecting the mortality and fall of large trees in the old-growth forest. To maintain, restore, and apply ecological knowledge in forest management practices, it is essential to further investigate ecosystem memory. This includes gaining a clearer understanding of species composition, the drivers of species shifts, and the processes by which ecosystems re-establish following disturbances, together with the legacies that persist. The findings indicate that further analyses and repeated future measurements are required to obtain a broader perspective and comparative data over longer time periods.Kirje Comparative growth modelling of genetically improved Norway spruce, Scots pine and silver birch forest stands(Estonian University of Life Sciences, 2025) Zeltinš, Pauls; Kangur, Ahto (advisor); Jansons, Āris (advisor); Institute of Forestry and Engineering; Linkevičius, Edgaras (opponent)ABSTRACT. This doctoral thesis focuses on advancing growth modelling for genetically improved forest reproductive material (FRM) of Norway spruce, Scots pine, and silver birch in the Baltic region. The use of genetically enhanced planting stock has become substantial to sustainable forest management in the region. This research aims to analyse growth patterns for improved FRM and develop individual tree height growth models addressing gaps in understanding of how genetic gains influence on growth dynamics. The study incorporated a dynamic generalized algebraic difference approach (GADA) form of the King-Prodan height growth functions previously calibrated from the remeasured National Forest Inventory plots in Latvia. The model showed stronger predictive accuracy for improved material compared to the unmodified reference function. New height growth models were developed for Scots pine and silver birch using dynamic growth functions with FRM-specific parameters. These models improved height predictions across various site qualities up to mid-rotation and demonstrated significant genetic gains in height growth, particularly for “tested” FRM categories. The clonal effect on Norway spruce growth was assessed using radial increment data, identifying substantial genetic variation in diameter growth. Genetic control of diameter stabilized after age of 40 years. Height growth reconstruction of Norway spruce clones with distinct productivity revealed variation among genotypes to meteorological conditions, such as winter temperature and summer drought. Fast-growing clones showed greater resistance to stress but slower recovery rates. Practical application of the improved growth models, quantifying the faster early growth of tested and qualified FRM, will benefit in a form of adjusted early thinning schedules. Incorporation of the finding of the genetically determined variation in tree stress response in long-term breeding program is essential for implementation of climate-smart forestry.