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Sirvi Autor "Jansons, Ā." järgi

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  • Pisipilt
    Kirje
    Carbon content of below–ground biomass of young Scots pines in Latvia
    (2017) Jansons, Ā.; Bārdulis, A.; Ķēniņa, L.; Lazdiņa, D.; Džeriņš, E.; Kāpostiņš, R.
    Forest ecosystems play crucial role in global carbon cycling, therefore, increasing afforestation of agricultural land in Europe has been recognized as important contribution of carbon sequestration. In carbon reporting systems, root carbon content (CC) default value has been set to 50%. The study aimed to estimate CC in below–ground biomass and in relation to tree age in young Scots pine stands on forest and former agricultural land. The below–ground CC of young (8 to 40 years) managed Scots pine (Pinus sylvestris L.) stands growing on nutrient poor mineral soils in Latvia was carried out. In total 62 sample trees (43 in forest land, 19 in former agricultural land) were randomly selected for destructive sampling to estimate the CC within below–ground biomass. Below–ground biomass weighted mean CC was 49.7 ± 0.4%, being slightly lower than the default CC value used to calculate carbon budgets. Root fractions stump, small roots (diameter 2–20 mm), coarse roots (diameter > 20 mm)) differed (p < 0.001) in their CC. Stumps (50.6 ± 0.6%) had highest (p < 0.001) CC in the below–ground biomass, followed by coarse (49.5 ± 0.4%) and small (49.1 ± 0.4%) roots, which did not differ from each other in their CC. Results demonstrated age–dependent increase of CC (p < 0.001) from 48.2 ± 0.3% to 51.7 ± 0.5%, indicating overestimation of the default value during the first two decades, but underestimation for older trees (24 to 40 years).
  • Pisipilt
    Kirje
    Intra–annual height growth of hybrid poplars in Latvia. Results from the year of establishment
    (2018) Šēnhofa, S.; Zeps, M.; Ķēniņa, L.; Neimane, U.; Kāpostiņš, R.; Kārkliņa, A.; Jansons, Ā.
    Fast growing hybrid poplars (Populus spp.) could be successfully used for bioenergy as well as wood production. Productivity of clones had been studied in Baltic States recently, however, little is known about the impact of weather conditions on poplar height growth, thus the potential effect of climate change. Therefore, the aim of this study was to characterize the intra– annual height growth of hybrid poplar clones in Latvia. Height increment of 12 hybrid poplar clones was measured on average with an 11–day interval in the first vegetation season in 2016. Annual shoot height was on average 81.0 ± 6.8 cm, significantly (p < 0.001) depending on the poplar clone. Use of long (0.5 m) instead of short (0.3 m) cuttings leaded to larger annual height increment during the year of establishment of the plantation. From June to September the mean growth intensity was 10 to 15 mm day-1 . The trend of height growth intensity, described by Gompertz model, indicated that the poplar clones with largest height had relatively fast increase of the growth intensity from June to July. Changes of growth intensity was linked both with the temperature and sum of precipitation. This tendency was not so pronounced for clones with largest height increment, emphasizing the importance of the phenotypic plasticity in selection of clones for plantations.
  • Pisipilt
    Kirje
    Production and profitability of low density Norway spruce (Picea abies (L.) Karst.) plantation at 50 years of age: case study from eastern Latvia
    (2018) Katrevičs, J.; Džeriņa, B.; Neimane, U.; Desaine, I.; Bigača, Z.; Jansons, Ā.
    Norway spruce (Picea abies (L.) Karst.) is one of the most important commercial tree species, for which wider spacing are being advocated to reduce management costs and improve radial growth. Nevertheless, little is known about tree and stand parameters at the larger age in stands of extremely low density. The aim of our study was to assess growth and economic profitability of 50 years old low density Norway spruce plantation in Latvia. Allometric parameters for all trees of Norway spruce clonal plantation planted in 1964 with two spacings (1×3 m and 5×5 m) were measured and profitability were estimated. Norway spruce plantation with wider (5×5 m) spacing ensured significantly larger tree diameter and height (35 cm and 25 m, respectively) than trees from higher density trial. However, mean net present value (3% interest rates) was non–significantly (P = 0.12) different between 5×5 m and 1×3 m spacings, 2,571.9 ± 355.6 and 3,085.8 ± 452.9 € ha-1 , respectively. Values observed in low density (5×5 m) plantation fitted well in the observation of impact of density and stand parameters drawn based on National inventory data, showing a considerable potential to use plantations with low density in practice.