Meteoroloģisko faktoru un stādmateriāla ietekme uz papeļu augšanu = Effect of meteorological factors and planting material on poplar growth

Forestry is challenged by the global demand for sustainable renewable resources. Fast-growing tree species are highly productive and pose the potential to increase roundwood and energy wood production. In Northern Europe, poplars (Populus spp.) and their hybrids are among the most productive tree species. The productivity of poplar plantations is mainly determined by selected clones. Northern European countries lack wide and systematic poplar breeding programs, therefore mainly uses clones that are imported from other European regions. Clones that are transferred northward from their parental species origin should be suitable to an altered length of the vegetation period and low temperatures during the winter season. Clonal testing before recommendation for their commercial use is topical also in Latvia. The thesis aims to characterize the growth of the poplar clones in Latvia and the factors affecting it. This thesis summarizes six thematically linked scientific publications, and their results indicate the significant effect of climatic factors on poplar growth. The radial growth of Populus clones is negatively affected by drought-related stress during the growing season and increased temperature range during the dormancy. Height growth is determined by clone and length of the cuttings, and faster-growing clones are more robust to the negative effect of meteorological factors during the growing season. The faster-growing clones are more likely to have damaged leading shoots by early autumn frost. Trees that have withered aboveground shoots by autumn frost are sprouting during the next growing season, but the regrowth is delayed. Winter frost damage is more likely for weakly growing clones. Overall, fast-growing clones with sufficient autumn and winter frost resistance and survival could be selected.