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Articles by Urban Nilsson

Category: Research article

article id 10707, category Research article
Martin Goude, Urban Nilsson, Euan Mason, Giulia Vico. (2022). Comparing basal area growth models for Norway spruce and Scots pine dominated stands. Silva Fennica vol. 56 no. 2 article id 10707. https://doi.org/10.14214/sf.10707
Keywords: Pinus sylvestris; basal area; Picea abies; National Forest Inventory; regression; difference equation; long-term experiment
Highlights: Models were developed that predict basal area growth for Scot pine and Norway spruce stands in Sweden; There were no apparent differences in the ability to predict basal area development between a linear regression model for basal area growth or a compatible growth and yields model for basal area; The model based on data from the 80s had similar performance as the models with data from the 2000s, showing that both can reliably be used to predict forest development.
Abstract | Full text in HTML | Full text in PDF | Author Info

Models that predict forest development are essential for sustainable forest management. Constructing growth models via regression analysis or fitting a family of sigmoid equations to construct compatible growth and yield models are two ways these models can be developed. In this study, four species-specific models were developed and compared. A compatible growth and yield stand basal area model and a five-year stand basal area growth model were developed for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). The models were developed using data from permanent inventory plots from the Swedish national forest inventory and long-term experiments. The species-specific models were compared, using independent data from long-term experiments, with a stand basal area growth model currently used in the Swedish forest planning system Heureka (Elfving model). All new models had a good, relatively unbiased fit. There were no apparent differences between the models in their ability to predict basal area development, except for the slightly worse predictions for the Norway spruce growth model. The lack of difference in the model comparison showed that despite the simplicity of the compatible growth and yield models, these models could be recommended, especially when data availability is limited. Also, despite using more and newer data for model development in this study, the currently used Elfving model was equally good at predicting basal area. The lack of model difference indicate that future studies should instead focus on model development for heterogeneous forests which are common but lack in growth and yield modelling research.

  • Goude, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, SE-230 53 Alnarp, Sweden ORCID https://orcid.org/0000-0002-2179-292X E-mail: martin.goude@slu.se (email)
  • Nilsson, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, SE-230 53 Alnarp, Sweden E-mail: urban.nilsson@slu.se
  • Mason, School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand E-mail: euan.mason@canterbury.ac.nz
  • Vico, Department of Crop Production Ecology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden E-mail: giulia.vico@slu.se
article id 10512, category Research article
Mateusz Liziniewicz, Ignacio Barbeito, Andis Zvirgzdins, Lars-Göran Stener, Pentti Niemistö, Nils Fahlvik, Ulf Johansson, Bo Karlsson, Urban Nilsson. (2022). Production of genetically improved silver birch plantations in southern and central Sweden. Silva Fennica vol. 56 no. 1 article id 10512. https://doi.org/10.14214/sf.10512
Keywords: Betula pendula; planting; generalized algebraic difference approach; genetic gain; stand basal area starting function
Highlights: The basal area development of genetically improved birch in Sweden was modeled using a generalized algebraic difference approach; The best model fit, both graphically and statistically was delivered by the Korf base model; The analysis of realized gain trial showed a stability of relative differences in basal area between tested genotypes.
Abstract | Full text in HTML | Full text in PDF | Author Info

Investing in planting genetically improved silver birch (Betula pendula Roth) in Swedish plantations requires understanding how birch stands will develop over their entire rotation. Previous studies have indicated relatively low production of birch compared to Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.). This could result from using unrepresentative basic data, collected from unimproved, naturally-regenerated birch (Betula spp.) growing on inventory plots often located in coniferous stands. The objective of this study was to develop a basal area development function of improved silver birch and evaluate production over a full rotation period. We used data from 52 experiments including planted silver birch of different genetic breeding levels in southern and central Sweden. The experimental plots were established on fertile forest sites and on former agricultural lands, and were managed with different numbers of thinnings and basal area removal regimes. The model best describing total stand basal area development was a dynamic equation derived from the Korf base model. The analysis of the realized gain trial for birch showed a good stability of the early calculated relative differences in basal area between tested genotypes over time. Thus, the relative difference in basal area might be with cautious used as representation of the realized genetic gain. On average forest sites in southern Sweden, improved and planted silver birch could produce between 6–10.5 m3 ha–1 year–1, while on fertile agriculture land the average productivity might be higher, especially with material coming from the improvement program. The performed analysis provided a first step toward predicting the effects of genetic improvement on total volume production and profitability of silver birch. However, more experiments are needed to set up the relative differences between different improved material.

  • Liziniewicz, The Forestry Research Institute of Sweden, Ekebo, SE-268 90 Svalöv, Sweden E-mail: mateusz.liziniewicz@skogforsk.se
  • Barbeito, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, Alnarp, Sweden; Université de Lorraine, AgroParisTech, INRAE, UMR Silva, Nancy, France E-mail: ignacio.barbeito@slu.se
  • Zvirgzdins, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, Box 49, 23053 Alnarp, Sweden E-mail: andis.zvirgzdins@slu.se (email)
  • Stener, The Forestry Research Institute of Sweden, Ekebo, SE-268 90 Svalöv, Sweden E-mail: lg.stener@telia.com
  • Niemistö, Natural Resources In-stitute Finland (Luke), Natural resources, Seinäjoki, Finland E-mail: pentti.niemisto@luke.fi
  • Fahlvik, The Forestry Research Institute of Sweden, Ekebo, SE-268 90 Svalöv, Sweden E-mail: nils.fahlvik@skogforsk.se
  • Johansson, Tönnersjöheden Experimental Forest, SLU, Simlångsdalen, Sweden E-mail: ulf.johansson@slu.se
  • Karlsson, The Forestry Research Institute of Sweden, Ekebo, SE-268 90 Svalöv, Sweden E-mail: curly.birch@gmail.com
  • Nilsson, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, Box 49, 23053 Alnarp, Sweden E-mail: urban.nilsson@slu.se
article id 10414, category Research article
Jouni Siipilehto, Micky Allen, Urban Nilsson, Andreas Brunner, Saija Huuskonen, Soili Haikarainen, Narayanan Subramanian, Clara Antón-Fernández, Emma Holmström, Kjell Andreassen, Jari Hynynen. (2020). Stand-level mortality models for Nordic boreal forests. Silva Fennica vol. 54 no. 5 article id 10414. https://doi.org/10.14214/sf.10414
Keywords: Norway spruce; Scots pine; simulation; broadleaved species; logistic function; period length; plot size
Highlights: Models were developed for predicting stand-level mortality from a large representative NFI data set; The logistic function was used for modelling the probability of no mortality and the proportion of basal area in surviving trees; The models take into account the variation in prediction period length and in plot size; The models showed good fit with respect to stand density, developmental stage and species structure, and showed satisfying fit in the independent data set of unmanaged spruce stands.
Abstract | Full text in HTML | Full text in PDF | Author Info

New mortality models were developed for the purpose of improving long-term growth and yield simulations in Finland, Norway, and Sweden and were based on permanent national forest inventory plots from Sweden and Norway. Mortality was modelled in two steps. The first model predicts the probability of survival, while the second model predicts the proportion of basal area in surviving trees for plots where mortality has occurred. In both models, the logistic function was used. The models incorporate the variation in prediction period length and in plot size. Validation of both models indicated unbiased mortality rates with respect to various stand characteristics such as stand density, average tree diameter, stand age, and the proportion of different tree species, Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and broadleaves. When testing against an independent dataset of unmanaged spruce-dominated stands in Finland, the models provided unbiased prediction with respect to stand age.

  • Siipilehto, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland E-mail: jouni.siipilehto@luke.fi (email)
  • Allen, Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forest and Forest Products, NO-1431 Ås, Norway; Larson and McGowin Inc., Mobile, AL 36607, USA ORCID https://orcid.org/0000-0002-7824-2849 E-mail: micky.allen@nibio.no
  • Nilsson, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, SE-23053 Alnarp, Sweden ORCID https://orcid.org/0000-0002-7624-4031 E-mail: urban.nilsson@slu.se
  • Brunner, Norwegian University of Life Sciences (NMBU), Faculty of Environmental Sciences and Natural Resource Management, NO-1432 Ås, Norway ORCID https://orcid.org/0000-0003-1668-9714 E-mail: andreas.brunner@nmbu.no
  • Huuskonen, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland ORCID https://orcid.org/0000-0001-8630-3982 E-mail: saija.huuskonen@luke.fi
  • Haikarainen, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland ORCID https://orcid.org/0000-0001-8703-3689 E-mail: soili.haikarainen@luke.fi
  • Subramanian, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, SE-23053 Alnarp, Sweden ORCID https://orcid.org/0000-0003-2777-3241 E-mail: narayanan.subramanian@slu.se
  • Antón-Fernández, Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forest and Forest Products, NO-1431 Ås, Norway ORCID https://orcid.org/0000-0001-5545-3320 E-mail: clara.anton.fernandez@nibio.no
  • Holmström, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, SE-23053 Alnarp, Sweden ORCID https://orcid.org/0000-0003-2025-1942 E-mail: emma.holmstrom@slu.se
  • Andreassen, Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forest and Forest Products, NO-1431 Ås, Norway ORCID https://orcid.org/0000-0003-4272-3744 E-mail: kjellandreassen@gmail.com
  • Hynynen, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland E-mail: jari.hynynen@luke.fi
article id 7738, category Research article
Samuel Egbäck, Bo Karlsson, Karl-Anders Högberg, Kenneth Nyström, Mateusz Liziniewicz, Urban Nilsson. (2018). Effects of phenotypic selection on height-diameter ratio of Norway spruce and Scots pine in Sweden. Silva Fennica vol. 52 no. 2 article id 7738. https://doi.org/10.14214/sf.7738
Keywords: Pinus sylvestris; Picea abies; genetic correlations; heritability; Genetic selection; slenderness
Highlights: Swedish plus-tree selection promoted less slender Norway spruce trees and more slender Scots pine trees compared to neighboring trees; Similar results were also found for progeny trials which indicated that genetics played a prominent role in phenotypic appearance.
Abstract | Full text in HTML | Full text in PDF | Author Info

Genetically improved Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) are extensively used in operational Swedish forestry plantations. However, relatively little is known about the stem slenderness (height-diameter ratio) of genetically improved material. Thus, in this study we investigated effects of plus-tree selection on stem slenderness of Norway spruce and Scots pine in Sweden by evaluating both the plus-tree selection and a large number of progeny trials. Species-specific models for predicting the height-diameter ratio were estimated using regression and mixed model approach. Our results show that phenotypic plus-tree selection promoted less slender Norway spruce trees and more slender Scots pine trees compared to neighboring trees. Similar results were also found for the progeny trials which indicated that genetics played a prominent role in the phenotypic appearance. Compared to the progeny of neighboring trees, Norway spruce plus-tree progenies had a 5.3% lower height-diameter ratio, while Scots pine plus-tree progenies had a 1.5% greater height-diameter ratio. The narrow sense heritability for height-diameter ratio was 0.19 for Norway spruce and 0.11 for Scots pine, indicating that it is possible to modify the height-diameter ratio by breeding. Correlation coefficients between breeding values for height-diameter ratio and diameter were negative for Scots pine (–0.71) and Norway spruce (–0.85), indicating that selection for diameter only would result in less slender stems of both species. Similar correlations were also found between breeding values for height-diameter ratio and height of Scots pine (–0.34) and Norway spruce (–0.74).

  • Egbäck, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: samuel.egback@slu.se (email)
  • Karlsson, Skogforsk, Ekebo, 268 90 Svalöv, Sweden E-mail: bo.karlsson@skogforsk.se
  • Högberg, Skogforsk, Ekebo, 268 90 Svalöv, Sweden E-mail: karl-anders.hogberg@skogforsk.se
  • Nyström, Swedish University of Agricultural Sciences, Department of Forest Resource Management, Skogsmarksgränd, 901 83 Umeå, Sweden E-mail: kenneth.nystrom@slu.se
  • Liziniewicz, Skogforsk, Ekebo, 268 90 Svalöv, Sweden E-mail: Mateusz.Liziniewicz@skogforsk.se
  • Nilsson, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: urban.nilsson@slu.se
article id 5662, category Research article
Samuel Egbäck, Urban Nilsson, Kenneth Nyström, Karl-Anders Högberg, Nils Fahlvik. (2017). Modeling early height growth in trials of genetically improved Norway spruce and Scots pine in southern Sweden. Silva Fennica vol. 51 no. 3 article id 5662. https://doi.org/10.14214/sf.5662
Keywords: Pinus sylvestris; Picea abies; individual tree growth model; genetic component; genetic multiplier; unimproved material; improved material
Highlights: The developed height growth model based on unimproved material predicted the development relatively well for genetically improved Norway spruce; For genetically improved Scots pine, however, the model needed to be modified; By incorporating a genetic component into the Scots pine model, the prediction errors were reduced.
Abstract | Full text in HTML | Full text in PDF | Author Info

Genetically improved Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) are used extensively in operational Swedish forestry plantations to increase production. Depending on the genetic status of the plant material, the current estimated genetic gain in growth is in the range 10–20% for these species and this is expected to increase further in the near future. However, growth models derived solely from data relating to genetically improved material in Sweden are still lacking. In this study we investigated whether an individual tree growth model based on data from unimproved material could be used to predict the height increment in young trials of genetically improved Norway spruce and Scots pine. Data from 11 genetic experiments with large genetic variation, ranging from offspring of plus-trees selected in the late 1940s to highly improved clonal materials selected from well performing provenances were used. The data set included initial heights at the age of 7–15 years and 5-year increments for almost 2000 genetic entries and more than 20 000 trees. The evaluation indicated that the model based on unimproved trees predicted height development relatively well for genetically improved Norway spruce and there was no need to incorporate a genetic component. However, for Scots pine, the model needed to be modified. A genetic component was developed based on the genetic difference recorded within each trial, using mixed linear models and methods from quantitative genetics. By incorporating the genetic component, the prediction errors were significantly reduced for Scots pine. This study provides the first step to incorporate genetic gains into Swedish growth models and forest management planning systems.

  • Egbäck, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: samuel.egback@slu.se (email)
  • Nilsson, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: urban.nilsson@slu.se
  • Nyström, Swedish University of Agricultural Sciences, Department of Forest Resource Management, Skogsmarksgränd, 901 83 Umeå, Sweden E-mail: kenneth.nystrom@slu.se
  • Högberg, Skogforsk, Ekebo, 268 90 Svalöv, Sweden E-mail: karl-anders.hogberg@skogforsk.se
  • Fahlvik, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: nils.fahlvik@slu.se
article id 933, category Research article
Per-Ola Hedwall, Harald Grip, Sune Linder, Lars Lövdahl, Urban Nilsson, Johan Bergh. (2013). Effects of clear-cutting and slash removal on soil water chemistry and forest-floor vegetation in a nutrient optimised Norway spruce stand. Silva Fennica vol. 47 no. 2 article id 933. https://doi.org/10.14214/sf.933
Keywords: Picea abies; logging residues; forest fertilisation; forest undergrowth; N-retention; nutrient leakage; whole-tree harvest
Abstract | Full text in HTML | Full text in PDF | Author Info
Fertilisation with nutrient optimisation has in Sweden resulted in large increases in volume growth in young stands of Norway spruce. There are, however, environmental concerns about repeated fertilisation and one is the risk of nutrient leakage to ground water resources and aquatic ecosystems after clear-cutting of such forests. The present study followed soil-water chemistry in optimised fertilised stands after clear-cutting, as well as effects of harvest of slash on nutrient leakage. Parts of a 30-year-old stand of Norway spruce, which had been subject to a nutrient optimisation experiment for 17 years, were clear-cut. A split-plot design with whole-tree harvesting as the sub-plot treatment was applied. Lysimeters were installed and soil-water sampled at nine occasions during the following four years. No significant effects of fertilisation on nitrate leaching were found, while harvest of slash reduced the concentration of Ca, DOC, DON, K, Mg, ammonium and nitrate, as well as pH in the soil solution. While no effects of fertilisation could be seen on the soil water concentration of N, the results indicate an interaction between fertilisation and harvest of slash on the concentration of nitrate in the soil solution. The results indicate that forest-floor vegetation plays an important role in the retention of N after clear-cutting of fertilised forests.
  • Hedwall, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences (SLU), P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: per-ola.hedwall@slu.se (email)
  • Grip, Department of Forest Ecology and Management, SLU, SE-901 83 Umeå, Sweden E-mail: harald@grip2.se
  • Linder, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences (SLU), P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: sune.linder@slu.se
  • Lövdahl, Department of Forest Ecology and Management, SLU, SE-901 83 Umeå, Sweden E-mail: ll@nn.se
  • Nilsson, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences (SLU), P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: urban.nilsson@slu.se
  • Bergh, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences (SLU), P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: johan.bergh@slu.se
article id 54, category Research article
Urban Nilsson, Björn Elfving, Kjell Karlsson. (2012). Productivity of Norway spruce compared to Scots pine in the interior of northern Sweden. Silva Fennica vol. 46 no. 2 article id 54. https://doi.org/10.14214/sf.54
Keywords: Pinus sylvestris; current annual increment; mean annual increment; Picea abies; site index; yield
Abstract | View details | Full text in PDF | Author Info
Productivity of Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) was studied in 12 paired plots in the interior of northern Sweden. Stands were established between 1928 and 1959; yield plots were established between 1974 and 1983 during pre-commercial thinning of the stands. Gross stem-wood production was significantly higher for Scots pine than for Norway spruce, stem-wood production by Norway spruce being 29.4% that of Scots pine. The site index for Norway spruce was lower than for Scots pine at all sites except one; the average difference in site index was 4.8 m. The simulated maximum mean annual increment (MAImax) during the rotation was 19% higher than the MAImax estimated with the site index for Scots pine, whereas simulated MAImax and MAImax estimated from the site index was about the same for Norway spruce. The simulations also indicated that MAI peaked about 50 years later for Norway spruce than for Scots pine. More small trees were included in the diameter distribution of Norway spruce than of Scots pine resulting in a lower stem-wood volume for Norway spruce when stands with the same dominant height were compared. This study shows that the difference in growth and rotation length between Scots pine and Norway spruce has implications when choosing which species to grow in the interior of northern Sweden.
  • Nilsson, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, Alnarp, Sweden E-mail: urban.nilsson@slu.se (email)
  • Elfving, SLU, Forest Ecology and Management, Umeå, Sweden E-mail: be@nn.se
  • Karlsson, SLU, Unit of Field Based Research, Asa, Sweden E-mail: kk@nn.se
article id 225, category Research article
Johan Bergh, Urban Nilsson, Harald Grip, Per-Ola Hedwall, Tomas Lundmark. (2008). Effects of frequency of fertilisation on production, foliar chemistry and nutrient leaching in young Norway spruce stands in Sweden. Silva Fennica vol. 42 no. 5 article id 225. https://doi.org/10.14214/sf.225
Keywords: boreal; sludge; wood-ash; N; P; K
Abstract | View details | Full text in PDF | Author Info
There is a great need to increase the production in Swedish forests to meet future demand from the forest industry and the bio-energy sector. One option to increase the production is to supply nutrients to young stands of Norway spruce. For the practical application it is important to develop and optimise fertilisation regimes in terms of production, economy and leaching of nutrients. The frequency of fertilisation is one important variable in the fertilisation regime, and this study aimed to study effects of different fertilisation frequencies on production and leaching of nitrogen. In 2001, five field experiments were established in southern, central and northern Sweden. Young stands of Norway spruce were fertilised every year, every second year and every third year. In addition, fertilisation with sludge pellets and wood-ash combined with nitrogen was investigated. The current annual increment after five years of treatment was significantly larger in fertilised than in unfertilised treatments. The difference in production between fertilisation every year and every second year was insignificant, while fertilisation every third year resulted in lower production. Sludge pellets and wood-ash fertilisation gave significantly lower production than fertilisation every second year even though approximately the same amount of nitrogen was applied. There was relatively little leaching of nitrate to ground water in all treatments; 0.6–1 kg N ha–1 a–1 from plots with fertilisation every year or every second year; and 2.7 kg N ha–1 a–1 from plots with fertilisation every third year. Most of the leaching was after the first fertilisation, in all treatments at all sites.
  • Bergh, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: johan.bergh@ess.slu.se (email)
  • Nilsson, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: un@nn.se
  • Grip, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: hg@nn.se
  • Hedwall, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: poh@nn.se
  • Lundmark, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: tl@nn.se

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