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Articles by Lars Rytter

Category: Research article

article id 10036, category Research article
Karin Hjelm, Lars Rytter. (2018). The demand of hybrid aspen (Populus tremula × P. tremuloides) on site conditions for a successful establishment on forest land. Silva Fennica vol. 52 no. 5 article id 10036. https://doi.org/10.14214/sf.10036
Highlights: Low pH (below 3.5) reduced growth, but not survival, in a greenhouse study; Site preparation methods did not affect survival in field, but differences were found for growth; Mounding had generally the best effect on growth; Clonal differences were found that could be useful for improving establishment and growth.

Hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is a deciduous tree species suitable for producing large amounts of renewable biomass during short rotations. Its potential under North European conditions could be largely extended if not only agricultural land but also forest land was used for cultivation. Unfortunately, the knowledge of appropriate forest site conditions and effects of site preparation methods on hybrid aspen establishment is limited. In this paper, two studies that explore these questions are presented. In the first study, the sensitivity to acid soils was tested under greenhouse conditions in two type of soils: a) peat soil limed to certain pH levels (3.4–5.7) and b) collected forest soils where pH varied from 3.9 to 5.3. The lowest pH level resulted in reduced growth, elsewhere no significant differences were found. The second study was applied in the field and investigated the effect of four site preparation methods on survival and growth. The methods were: 1) control with no site preparation, 2) patch scarification, 3) mounding and 4) soil inversion. While no differences were found for survival, mounding was generally the method with the highest growth and patch scarification was least successful. The result was probably an effect of good soil aeration and less competition from vegetation after mounding. The field study also revealed clonal differences in growth performance, which stresses the importance of clone selection prior to planting. The results of these studies indicate that hybrid aspen is less sensitive to variation in pH and site preparation methods compared with other poplar species, as have been found in similar studies.

  • Hjelm, Skogforsk, Ekebo 2250, SE-268 90 Svalöv, Sweden ORCID ID:E-mail: karin.hjelm@skogforsk.se (email)
  • Rytter, Skogforsk, Ekebo 2250, SE-268 90 Svalöv, Sweden ORCID ID: http://orcid.org/0000-0001-6183-4832 E-mail: lars.rytter@skogforsk.se
article id 1713, category Research article
Lars-Göran Stener, Lars Rytter, Gunnar Jansson. (2017). Effects of pruning on wood properties of planted silver birch in southern Sweden. Silva Fennica vol. 51 no. 2 article id 1713. https://doi.org/10.14214/sf.1713
Highlights: Pruning silver birch trees increased the production of defect-free wood outside the knots; Most wood defects were found inside the knots; Pruned birch trees provide butt logs with higher value than unpruned trees.

Pruning was performed at midsummer in two genetically homogenous and managed planted silver birch stands in southern Sweden – one aged 9 and one aged 10 years. Wood defects were analysed 10 years thereafter, using the five uppermost twigs of the stems up to a height of 30 dm. The number of trees examined at each site was around 70, of which half were pruned. The main findings were that: a) compared to unpruned trees, pruned trees produced more defect-free wood outside the knots; b) most wood defects were found inside the knots; and c) wood defects like rot and bark ingrowth were similar for pruned and unpruned trees, while discolouration was marginally higher for pruned trees inside knots but similar outside knots. Overall, the results confirm previous findings that pruned birch trees will provide butt logs with higher value than unpruned trees.

  • Stener, The Forestry Research Institute of Sweden, Ekebo 2250, 268 90 Svalöv, Sweden ORCID ID:E-mail: lars-goran.stener@skogforsk.se (email)
  • Rytter, The Forestry Research Institute of Sweden, Ekebo 2250, 268 90 Svalöv, Sweden ORCID ID:E-mail: lars.rytter@skogforsk.se
  • Jansson, The Forestry Research Institute of Sweden, Uppsala Science Park, 751 83 Uppsala, Sweden ORCID ID:E-mail: gunnar.jansson@skogforsk.se
article id 189, category Research article
Lars Rytter, Gunnar Jansson. (2009). Influence of pruning on wood characters in hybrid aspen. Silva Fennica vol. 43 no. 4 article id 189. https://doi.org/10.14214/sf.189
Fast-growing hybrid aspens (Populus tremula L. x P. tremuloides Michx.) are currently of great interest in Sweden since they can produce biomass at high rates and, at the same time, can be used to produce higher value wood products. This study focuses on the effects of pruning hybrid aspen to improve its wood quality. About 50% of the trees in the experimental stand were pruned by removing twigs, at heights up to 4 m, when they were 7–8 years old. Ten years later, 20 pruned and 20 unpruned trees, representing four clones, were randomly selected. Ten knots or twig/stem junctions, respectively, per tree were exposed for inspection using a chain saw and examined. The results revealed that pruned trees cicatrised the knots within about three years and thereafter produced substantial amounts of faultless wood. In contrast, unpruned trees (which had retained almost 80% of their twigs, often as dry twigs with bark pockets) had produced small uneven amounts of quality wood. Removal of twigs with acute angles and/or large diameters resulted in greater colour defects and rot in annual rings outside the pruning position, but the time of cicatrisation was not significantly affected. The results show that pruning can be used to enhance the wood quality of hybrid aspen over a short time period, and that pruning should be performed early during the rotation period when branches are small, in order to minimize discolouration and rot in the new annual rings.
  • Rytter, The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-26890 Svalöv ORCID ID:E-mail: lars.rytter@skogforsk.se (email)
  • Jansson, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala ORCID ID:E-mail:
article id 491, category Research article
Lars Rytter, Lars-Göran Stener. (2003). Clonal variation in nutrient content in woody biomass of hybrid aspen (Populus tremula L. x P. tremuloides Michx.). Silva Fennica vol. 37 no. 3 article id 491. https://doi.org/10.14214/sf.491
Differences in the nutrient concentrations and nutrient amounts of stems and branches amongst clones of hybrid aspen (Populus tremula L. x P. tremuloides Michx.) were investigated. Seven clones with superior and seven with medium growth rates were selected from a test of 119 clones in southern Sweden. Four trees per clone were randomly identified and harvested in dormant conditions. Sample discs from the stems and branches were collected and analysed for N, K, P, Ca, Mg, and S concentrations, as well as wood density. The analyses revealed significant genetic differences in wood density, K, P, and Mg concentrations in the stems. There were weak (non-significant) and negative genetic correlations between stem volume and concentrations of all the nutrients, except potassium, suggesting that nutrient-efficient clones could be selected without significantly sacrificing genetic gain for growth. In the branches K, Ca, and Mg concentrations differed significantly among clones. After selecting more nutrient efficient clones, the potential savings of nutrients compared with current hybrid aspen material was estimated to be around 5%, which seems fairly low, at least in a short-term perspective. However, the use of clones with different nutrient storage strategies may be regarded as a possible way in the long run to save nutrients in hybrid aspen ecosystems, or of removing them when sludge is applied.
  • Rytter, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-26890, Svalöv, Sweden ORCID ID:E-mail: lars.rytter@skogforsk.se (email)
  • Stener, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-26890, Svalöv, Sweden ORCID ID:E-mail:

Category: Review article

article id 1660, category Review article
Lars Rytter, Morten Ingerslev, Antti Kilpeläinen, Piritta Torssonen, Dagnija Lazdina, Magnus Löf, Palle Madsen, Peeter Muiste, Lars-Göran Stener. (2016). Increased forest biomass production in the Nordic and Baltic countries – a review on current and future opportunities. Silva Fennica vol. 50 no. 5 article id 1660. https://doi.org/10.14214/sf.1660
Highlights: Annual growth is 287 million m3 in the forests of the Nordic and Baltic countries; Growth can be increased by new tree species, tree breeding, high-productive management systems, fertilization and afforestation of abandoned agricultural land; We predict a forest growth increment of 50–100% is possible at the stand scale; 65% of annual growth is harvested today.

The Nordic and Baltic countries are in the frontline of replacing fossil fuel with renewables. An important question is how forest management of the productive parts of this region can support a sustainable development of our societies in reaching low or carbon neutral conditions by 2050. This may involve a 70% increased consumption of biomass and waste to meet the goals. The present review concludes that a 50–100% increase of forest growth at the stand scale, relative to today’s common level of forest productivity, is a realistic estimate within a stand rotation (~70 years). Change of tree species, including the use of non-native species, tree breeding, introduction of high-productive systems with the opportunity to use nurse crops, fertilization and afforestation are powerful elements in an implementation and utilization of the potential. The productive forests of the Nordic and Baltic countries cover in total 63 million hectares, which corresponds to an average 51% land cover. The annual growth is 287 million m3 and the annual average harvest is 189 million m3 (65% of the growth). A short-term increase of wood-based bioenergy by utilizing more of the growth is estimated to be between 236 and 416 TWh depending on legislative and operational restrictions. Balanced priorities of forest functions and management aims such as nature conservation, biodiversity, recreation, game management, ground water protection etc. all need consideration. We believe that these aims may be combined at the landscape level in ways that do not conflict with the goals of reaching higher forest productivity and biomass production.

  • Rytter, The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-26890 Svalöv, Sweden ORCID ID:E-mail: lars.rytter@skogforsk.se (email)
  • Ingerslev, Copenhagen University, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, DK-1958, Frederiksberg C, Denmark ORCID ID:E-mail: moi@ign.ku.dk
  • Kilpeläinen, Finnish Environment Institute, Joensuu Office, P.O. Box 111, FI-80101 Joensuu, Finland; University of Eastern Finland, Faculty of Science and Forestry, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland ORCID ID:E-mail: antti.kilpelainen@ymparisto.fi
  • Torssonen, University of Eastern Finland, Faculty of Science and Forestry, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland ORCID ID:E-mail: Piritta.Torssonen@uef.fi
  • Lazdina, Latvian State Forest Research Institute “Silava”, 111 Riga str, Salaspils, LV 2169 Latvia ORCID ID:E-mail: Dagnija.Lazdina@silava.lv
  • Löf, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, Box 49 SE-230 53 Alnarp, Sweden ORCID ID:E-mail: magnus.lof@slu.se
  • Madsen, Copenhagen University, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, DK-1958, Frederiksberg C, Denmark ORCID ID:E-mail: pam@ign.ku.dk
  • Muiste, Estonian University of Life Sciences, Institute of Forestry and Rural Engineering, Dept. Forest Industry, Kreutzwaldi 5, Tartu 51014, Estonia ORCID ID:E-mail: Peeter.Muiste@emu.ee
  • Stener, The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-26890 Svalöv, Sweden ORCID ID:E-mail: Lars-Goran.Stener@skogforsk.se

Category: Research note

article id 1126, category Research note
Rebecka Mc Carthy, Per Magnus Ekö, Lars Rytter. (2014). Reliability of stump sprouting as a regeneration method for poplars: clonal behavior in survival, sprout straightness and growth. Silva Fennica vol. 48 no. 3 article id 1126. https://doi.org/10.14214/sf.1126
Highlights: Clonal differences were found in stump sprout survival; Clonal differences occurred in sprout straightness; It is uncertain if the ability to produce a high number of stump sprouts is beneficial.
The interest in poplars (Populus spp.) has increased globally as a result of the current incentive to expand the use of biomass for energy. So far, knowledge about poplar stump sprouting is generally poor. The objective of this study was to investigate poplar stump sprouting as regeneration method in harvested plantations. A 19-year-old poplar clonal test, including 23 different clones, on former arable land was harvested in the winter. After one year, stumps were assessed for sprout survival, sprout straightness, number of sprouts, sprout height and basal diameter. Differences between clones were found for survival and sprout straightness. Clonal differences were also found in mean size of sprouts (basal diameter and height). However, no differences were found between clones when comparing size of the tallest sprout or number of sprouts produced on stumps. This study indicates that stump sprouts from various poplar clones differ in survival, sprout straightness and mean growth, which should be taken into account when planning for the next tree generation. The study needs to be complemented with other studies to better assess sprouting characteristics for different clones.
  • Mc Carthy, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-268 90 Svalöv, Sweden & Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, P.O. Box 49, SE-230 53 Alnarp, Sweden ORCID ID:E-mail: rebecka.mccarthy@skogforsk.se (email)
  • Ekö, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, P.O. Box 49, SE-230 53 Alnarp, Sweden ORCID ID:E-mail: Per.Magnus.Eko@slu.se
  • Rytter, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-268 90 Svalöv, Sweden ORCID ID:E-mail: lars.rytter@skogforsk.se

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