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Rytter L.,Forestry Research Institute of Sweden
Forest Ecology and Management | Year: 2013

Early management of hardwood stands is important if the goal is to produce high-quality timber and it may also reduce the rotation period. Both effects are favourable for the economic outcome of hardwood forestry. Eight young hardwood stands, dominated by either birch (Betula pendula Roth and B. pubescens Ehrh.), black alder (Alnus glutinosa (L.) Gaertn.), aspen (Populus tremula L.) or lime (Tilia cordata Mill.), in need of precommercial thinning, were identified in southern Sweden. The aim was to assess the effect of delayed thinning and thinning intensity on retained trees under north European conditions. Three treatments were applied: (1) 5. years delayed thinning, (2) standard thinning, and (3) strong thinning to 2/3 the stand density of treatment 2. Retained trees were followed during 11. years and showed that delayed thinning resulted in smaller crowns and slower diameter development than in the thinned alternatives. There were only minor differences between standard and strong thinning. After thinning the trees of the delayed thinning alternative showed partial recovery of the crowns. There were no longer any significant differences in green crown base height although differences in green crown radius and crown ratio remained between the delayed and the other two thinning alternatives. Furthermore, diameter growth rate of the delayed thinning trees recovered to about the same level as for trees with earlier thinning. However, differences in diameter and in the ratio diameter:height persisted, indicating that diameter loss in the early rotation phase cannot be compensated for later. It is concluded that early precommercial thinning lead to better early diameter growth than delayed thinning but also that young stands with late thinning can recover in diameter growth rate resulting in shifted but parallel diameter growth curves. © 2013 Elsevier B.V. Source

Almqvist C.,Forestry Research Institute of Sweden
Canadian Journal of Forest Research | Year: 2013

Reducing generation turnover in breeding programs should increase the genetic gain per unit time. This could potentially be achieved by topgrafting, since it can be used to induce strobili production in young plant material. I therefore studied the effect of the interstock clone on the vitality and strobili production of topgrafts in Pinus sylvestris L. over 4 years. The experiment consisted of 20 interstock clones × 3 ramets per interstock × 10 topgrafts per ramet, giving a total of 600 topgrafts. There were large differences in topgraft survival rates among the different interstock clones, ranging from 60% to 93% in the spring of the experiment's fourth year. Analysis of variance (ANOVA) revealed that both the interstock and the topgraft had significant effects on female and male topgraft strobili production. The effect of the ramet within the interstock was small on topgraft vitality but was large and significant on strobili production. The interaction between interstock and topgraft was not significant for topgraft vitality and male strobili production for any of the studied years, but it was significant two out of four years for female strobili production. No relationship was found between female strobili production on the interstocks and their capacity to induce female strobilis on topgrafts, but there was a weak relationship between strobili production on the interstocks and their capacity to induce male strobilis on topgrafts. Overall, the results indicate that topgrafting could, with appropriate interstock clones, effectively decrease the time to strobili production compared with conventional grafting using young rootstocks in P. sylvestris, but suitable interstock clones will have to be identified by screening tests. © 2013 Published by NRC Research Press. Source

Rosner S.,University of Natural Resources and Life Sciences, Vienna | Karlsson B.,Forestry Research Institute of Sweden
Trees - Structure and Function | Year: 2011

The aim of this study was to investigate bending stiffness and compression strength perpendicular to the grain of Norway spruce (Picea abies (L.) Karst.) trunkwood with different anatomical and hydraulic properties. Hydraulically less safe mature sapwood had bigger hydraulic lumen diameters and higher specific hydraulic conductivities than hydraulically safer juvenile wood. Bending stiffness (MOE) was higher, whereas radial compression strength lower in mature than in juvenile wood. A density-based tradeoff between MOE and hydraulic efficiency was apparent in mature wood only. Across cambial age, bending stiffness did not compromise hydraulic efficiency due to variation in latewood percent and because of the structural demands of the tree top (e. g. high flexibility). Radial compression strength compromised, however, hydraulic efficiency because it was extremely dependent on the characteristics of the "weakest" wood part, the highly conductive earlywood. An increase in conduit wall reinforcement of earlywood tracheids would be too costly for the tree. Increasing radial compression strength by modification of microfibril angles or ray cell number could result in a decrease of MOE, which would negatively affect the trunk's capability to support the crown. We propose that radial compression strength could be an easily assessable and highly predictive parameter for the resistance against implosion or vulnerability to cavitation across conifer species, which should be topic of further studies. © 2010 Springer-Verlag. Source

Lindholm E.-L.,Swedish University of Agricultural Sciences | Berg S.,Forestry Research Institute of Sweden | Hansson P.-A.,Swedish University of Agricultural Sciences
European Journal of Forest Research | Year: 2010

In a case study, seven different procurement chains of forest energy in Sweden were modelled and the environmental performance was calculated from a Life Cycle Assessment (LCA) perspective. The systems differed with respect to geographical location, the technology employed and resource use (stumps or logging residues). The energy output/input ratio of chips from residues and stumps was in the range 21-48, and the greenhouse gas emissions were 1.5-3.5 g CO2-eq/MJ chips. The systems in southern Sweden were generally more efficient than similar systems in northern Sweden. The forest energy systems based on bundles and stumps rely on immature technologies which have the potential to be improved should there be technical developments of the systems. © 2010 Springer-Verlag. Source

Rytter R.-M.,Forestry Research Institute of Sweden
Biomass and Bioenergy | Year: 2012

A large share, estimated at 12-25%, of the annual anthropogenic greenhouse gas emissions is attributed to global deforestation. Increasing the forested areas therefore has a positive impact on carbon (C) sequestration and mitigation of high atmospheric CO2 concentrations. Fast-growing species, such as willow and poplar, are of high interest as producers of biomass for fuel, but also as C sinks. The present study estimated the rate of C sequestration in biomass and soil in willow and poplar plantations. Calculations were based on above- and below-ground biomass production data from field experiments, including fine root turnover, litter decomposition rates, and production levels from commercial plantations. Accumulation of C in woody biomass, above and below ground, was estimated at 76.6-80.1 Mg C ha-1 and accumulation of C in the soil at 9.0-10.3 Mg C ha-1 over the first 20-22 years. The average rates of C sequestration were 3.5-4.0 Mg C ha-1 yr-1 in woody biomass, and 0.4-0.5 Mg C ha-1 yr-1 in the soil. If 400,000 ha of abandoned arable land in Sweden were planted with willow and poplar, about 1.5 Tg C would be sequestered annually in woody biomass and 0.2 Tg C in soils. This would be nearly one tenth of the annual anthropogenic emissions of C in Sweden today. These calculations show the potential of fast-growing plantations on arable land to mitigate the effect of high CO2 concentrations over a short time span. Knowledge gaps were found during the calculation process and future research areas were suggested. © 2011 Elsevier Ltd. Source

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