Articles by Lars Rytter

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 E-mail: karin.hjelm@skogforsk.se
• Rytter, Skogforsk, Ekebo 2250, SE-268 90 Svalöv, Sweden http://orcid.org/0000-0001-6183-4832 E-mail: lars.rytter@skogforsk.se

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 E-mail: lars-goran.stener@skogforsk.se
• Rytter, The Forestry Research Institute of Sweden, Ekebo 2250, 268 90 Svalöv, Sweden E-mail: lars.rytter@skogforsk.se
• Jansson, The Forestry Research Institute of Sweden, Uppsala Science Park, 751 83 Uppsala, Sweden E-mail: gunnar.jansson@skogforsk.se

• Rytter, The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-26890 Svalöv E-mail: lars.rytter@skogforsk.se
• Jansson, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala E-mail: gj@nn.se

• Rytter, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-26890, Svalöv, Sweden E-mail: lars.rytter@skogforsk.se
• Stener, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-26890, Svalöv, Sweden E-mail: lgs@nn.se

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 E-mail: lars.rytter@skogforsk.se
• Ingerslev, Copenhagen University, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, DK-1958, Frederiksberg C, Denmark 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 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 E-mail: Piritta.Torssonen@uef.fi
• Lazdina, Latvian State Forest Research Institute “Silava”, 111 Riga str, Salaspils, LV 2169 Latvia E-mail: Dagnija.Lazdina@silava.lv
• Löf, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, Box 49 SE-230 53 Alnarp, Sweden E-mail: magnus.lof@slu.se
• Madsen, Copenhagen University, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, DK-1958, Frederiksberg C, Denmark 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 E-mail: Peeter.Muiste@emu.ee
• Stener, The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-26890 Svalöv, Sweden E-mail: Lars-Goran.Stener@skogforsk.se

• 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 E-mail: rebecka.mccarthy@skogforsk.se
• Ekö, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, P.O. Box 49, SE-230 53 Alnarp, Sweden E-mail: Per.Magnus.Eko@slu.se
• Rytter, Forestry Research Institute of Sweden, Skogforsk, Ekebo 2250, SE-268 90 Svalöv, Sweden E-mail: lars.rytter@skogforsk.se