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Silva Fennica 1926-1997
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Articles by Kjell Andreassen

Category: Research article

article id 10187, category Research article
Timo Pukkala, Kjersti Holt Hanssen, Kjell Andreassen. (2019). Stem taper and bark functions for Norway spruce in Norway. Silva Fennica vol. 53 no. 3 article id 10187. https://doi.org/10.14214/sf.10187
Highlights: New variable-exponent stem taper and bark functions were developed for Norway spruce; Both fixed and mixed-effects models were developed; Site index and tree age had statistically significant but small effects on stem taper.

Based on data from long-term experimental fields with Norway spruce (Picea abies (L.) H. Karst.), we developed new stem taper and bark functions for Norway. Data was collected from 477 trees in stands across Norway. Three candidate functions which have shown good performance in previous studies (Kozak 02, Kozak 97 and Bi) were fitted to the data as fixed-effects models. The function with the smallest Akaike Information Criterion (AIC) was then chosen for additional analyses, fitting 1) site index-dependent and 2) age-dependent versions of the model, and 3) fitting a mixed-effects model with tree-specific random parameters. Kozak 97 was found to be the function with the smallest AIC, but all three tested taper functions resulted in fairly similar predictions of stem taper. The site index-dependent function reduced AIC and residual standard error and showed that the effect of site index on stem taper is different in small and large trees. The predictions of the age-independent and age-dependent models were very close to each other. Adding tree-specific random parameters to the model clearly reduced AIC and residual variation. However, the results suggest that the mixed-effects model should be used only when it is possible to calibrate it for each tree, otherwise the fixed-effects Kozak 97 model should be used. A model for double bark thickness was also fitted as fixed-effects Kozak 97 model. The model behaved logically, predicting larger relative but smaller absolute bark thickness for small trees.

article id 1781, category Research article
Petr Čermák, Michal Rybníček, Tomáš Žid, Kjell Andreassen, Isabella Børja, Tomáš Kolář. (2017). Impact of climate change on growth dynamics of Norway spruce in south-eastern Norway. Silva Fennica vol. 51 no. 2 article id 1781. https://doi.org/10.14214/sf.1781
Highlights: Correlations between tree-ring width and climate parameters showed temporal instability in their relationship during the period 1915–2012; A statistically significant positive correlation of April–May precipitation on tree-ring growth was identified since the mid-1970s; The concomitant temperature increase may have contributed to the changes of growth dynamics.

The ongoing climate change may have a distinct effect on Norway spruce growth, one of the most important tree species in European forest management. Therefore, the understanding and assessment of climate-growth relationship can help to reveal relevant patterns in temporal variability that may result in lower tree vitality and decline. The main objective of our study was to evaluate the long-term climate-growth variability of Norway spruce in south-eastern Norway, at the northern edge of the temperate zone. We sampled in total 270 dominant and co-dominant trees from 18 plots in south-eastern Norway. We analysed stem cores and evaluated crown condition parameters to assess the retrospective tree growth and vitality. Despite considerable differences in the crown parameters, high similarity among tree-ring width (TRW) series allowed compiling the regional tree-ring width chronology. Correlations between TRW and climate parameters showed temporal instability in their relationship during the period 1915–2012. While we did not detect any significant relationships between TRW and climate parameters in the first half of the study period (1915–1963), a significant correlation between TRW and spring precipitation was observed for the period 1964–2012. This shift appeared concurrent with temperatures reaching above-average values compared to the average of the climate normal period 1961–1990.

  • Čermák, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic ORCID ID:E-mail: cermacek@mendelu.cz (email)
  • Rybníček, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic; Global Change Research Institute, The Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic ORCID ID:E-mail: michalryb@post.cz
  • Žid, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic ORCID ID:E-mail: tom.z@centrum.cz
  • Andreassen, Norwegian Institute of Bioeconomy Research (NIBIO), P.O. Box 115, NO-1431 Ås, Norway ORCID ID:E-mail: Kjell.Andressen@nibio.no
  • Børja, Norwegian Institute of Bioeconomy Research (NIBIO), P.O. Box 115, NO-1431 Ås, Norway ORCID ID:E-mail: Isabella.Borja@nibio.no
  • Kolář, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic; Global Change Research Institute, The Czech Academy of Sciences, Bělidla 986/4a, 603 00 Brno, Czech Republic ORCID ID:E-mail: koldatom@gmail.com

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