Current issue: 53(3)

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Silva Fennica 1926-1997
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Acta Forestalia Fennica
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Articles by Urban Bergsten

Category: Research article

article id 1563, category Research article
Kristina Ahnlund Ulvcrona, Dan Bergström, Urban Bergsten. (2017). Stand structure after thinning in 1–2 m wide corridors in young dense stands. Silva Fennica vol. 51 no. 3 article id 1563. https://doi.org/10.14214/sf.1563
Highlights: Boom corridor thinning (BCT) results in more stand structure heterogeneity than conventional thinning or pre-commercial thinning (PCT), maintaining both smaller-diameter trees and deciduous species; Neither dominant height nor number of possible future crop trees is jeopardized, and boom corridor thinning results in higher values of stem volume and biomass; The technique is flexible as various corridor types give similar stand structure results.

Boom corridor thinning (BCT) has been proposed as a cost-effective technique for biomass thinning (BT) in young dense stands. The objective of this study was to determine how various BCT operations affect stand structure following biomass thinning and to compare the results with conventional selective thinning methods. Two series of field experiments were established; BCT 1-series: Three sites in south of Sweden (9 and 11 m in mean and dominating tree height) with five treatments, including a control, conventional selective thinning and three BCT treatments (1 m and 2 m wide corridors and selective BCT). The second BCT series: Three regions in Sweden (in the north, centre and in the south), with two stand sites in each region with different tree heights (4/9 m and 5/10 m in mean/dominating tree height). Treatments were control, pre-commercial thinning (PCT), conventional selective thinning and BCT (high and low thinning). Following the first biomass thinning, BCT regimes and selective thinning methods resulted in similar stand structures based on the number of possible future crop trees (>80 mm in diameter at breast height). However, BCT maintained a higher diversity of tree sizes as well as more stems per hectare, including deciduous species, than the selective thinning approaches. The stands after BCT should have more vertical complexity, especially when compared to pre-commercial thinning. The structural heterogeneity resulting from BCT may also increase stand biodiversity and ecosystem service values.

  • Ahnlund Ulvcrona, Swedish University of Agricultural Sciences (SLU), Department of Forest Biomaterials and Technology (SBT), Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: kristina.ulvcrona@slu.se (email)
  • Bergström, Swedish University of Agricultural Sciences (SLU), Department of Forest Biomaterials and Technology (SBT), Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: dan.bergstrom@slu.se
  • Bergsten, Swedish University of Agricultural Sciences (SLU), Department of Forest Biomaterials and Technology (SBT), Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
article id 1064, category Research article
Back Tomas Ersson, Urban Bergsten, Ola Lindroos. (2014). Reloading mechanized tree planting devices faster using a seedling tray carousel. Silva Fennica vol. 48 no. 2 article id 1064. https://doi.org/10.14214/sf.1064
Highlights: Seedling reloading onto the Bracke Planter crane-mounted planting device was twice as fast with the MagMat tray-wise-loaded carousel as today’s seedling-wise-loaded carousel; Tray-wise reloading combined with deplugging seedlings from suitable cultivation trays has the potential to be an efficient and robust way to feed seedlings on any type of tree planting machine.
On Nordic clearcuts, today’s tree planting machines produce high-quality but costly regenerations. Much of this high cost is attributable to the planting machines’ low productivity. One promising way of raising productivity is to lessen the time spent manually reloading seedlings onto the carousels of crane-mounted planting devices. Using MagMat, a carousel test-rig designed by engineering students, we studied how much faster tray-wise seedling reloading is on the Bracke Planter compared to reloading with today’s seedling-wise-loaded carousel. The MagMat test-rig held eight Hiko cultivation trays from which seedlings were deplugged individually and dropped into the planting tube. The time study confirmed that seedling reloading was on average twice as fast with MagMat compared to today’s seedling carousel, thereby increasing assumed planting machine productivity by 8–9% depending on the planting device used. MagMat’s cost-efficiency was analysed to be particularly reliant on its added investment cost, mechanical availability and how quickly trays can be switched automatically. Nevertheless, MagMat’s field performance illustrated the overall potential of tray-wise loading compared to piecewise seedling loading for increasing the productivity of crane-mounted planting devices. Also, deplugging proved to be a reliable method of extracting seedlings from the rigid, copper-painted Hiko cultivation trays even when performed at the excavator’s boom-tip during mounding work. We conclude that, rather than piecewise seedling loading, tray-wise loading combined with deplugging seedlings from suitable cultivation trays is a reliable and much more time-efficient method to feed seedlings on probably any type of tree planting machine.
  • Ersson, Department of Forest Biomaterials and Technology, SLU, SE-90183 Umeå, Sweden ORCID ID:E-mail: back.tomas.ersson@slu.se (email)
  • Bergsten, Department of Forest Biomaterials and Technology, SLU, SE-90183 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
  • Lindroos, Department of Forest Biomaterials and Technology, SLU, SE-90183 Umeå, Sweden ORCID ID:E-mail: ola.lindroos@slu.se
article id 938, category Research article
Lars Karlsson, Tommy Mörling, Urban Bergsten. (2013). Influence of silvicultural regimes on the volume and proportion of juvenile and mature wood in boreal Scots pine. Silva Fennica vol. 47 no. 4 article id 938. https://doi.org/10.14214/sf.938
Highlights: Initial stand densities have a large impact on the proportion of mature wood within trees throughout most of their life cycle; The difference between regimes in volume of long fibres in crop trees could be substantial; Long-term silvicultural strategies implemented at juvenile stand ages can be important tools in order to produce wood raw material suited for specific end-uses.
Trees from 48 to 78 years old, exposed to three different long-term silvicultural regimes, were examined for transition ages between juvenile (JW), transition (TW) and mature wood (MW), total wood volume and proportions of the same wood types, as defined by fibre length. Twenty one sample trees were collected at sites with similar growing conditions within the same geographical area. Stem discs and fibre samples from breast height (BRH), 20% of tree height, green crown height and 70% of tree height were analysed. Trees growing in an environment with few neighboring trees (Sparse regime) started to produce MW, on average, five years later at BRH and six to nine years later at 20% of total tree height than trees in stands with high stem numbers (Dense regime) and trees growing in stands where the stem number had been heavily reduced after an initial high stand density (Dense/Sparse regime). For all regimes, the greatest mean fibre length was found below the green crown and high initial stem numbers were found to positively influence fibre length. The proportion of MW in the whole stem was 34% at Sparse regime sites, 57–69% at Dense/Sparse sites and 63–64% in sites where there was a Dense regime. The proportion of MW was significantly lower for trees from the Sparse regime on each stem section compared. In conclusion, the results suggest that the initial condition a tree faces affects the stem wood properties and quality output at the end of the rotation period.
  • Karlsson, Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden ORCID ID:E-mail: lars.karlsson@slu.se (email)
  • Mörling, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden ORCID ID:E-mail: tommy.morling@slu.se
  • Bergsten, Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
article id 958, category Research article
Back Tomas Ersson, Linus Jundén, Urban Bergsten, Martin Servin. (2013). Simulated productivity of one- and two-armed tree planting machines. Silva Fennica vol. 47 no. 2 article id 958. https://doi.org/10.14214/sf.958
Highlights: Using discrete-event simulation and detailed terrain and machine models, the productivities of excavator-based one- and two-armed tree planting machines were simulated; The machines’ arms were equipped with one-and two-headed planting devices; Two planting heads per arm rather than two arms per base machine is better for increasing the productivity of intermittently advancing planting machines on Nordic clearcuts.
To increase mechanized planting, planting machine productivity must increase in order to improve cost-efficiency. To determine if excavators with two crane arms could potentially help to increase planting machine productivity under Nordic clearcut conditions, we modelled one-armed and semi-automated two-armed excavators with one- and two-headed planting devices. Using a recently developed tool for discrete-event simulation, these machine models then mounded and planted seedlings on terrain models with moraine soil having various frequencies of obstacles (stumps, roots and stones). Compared to if the two heads were mounted pairwise on only one arm, the results showed that productivity did not increase if two planting heads were attached individually to two separate crane arms. But productivity did increase if the planting machine had four planting heads mounted pairwise on two separate arms. However, despite assuming automated mounding and crane motion between planting spots, the two-armed, four-headed model never achieved high enough productivity levels to make it more cost-efficient than one-armed machines. The simulations illustrate that our terrain models generate realistic root architecture and boulder content distributions in moraine soil, while our machine models functionally describe mechanized planting work. Based on our assumptions, we conclude that further development work on two-armed excavator-based planting machines for Nordic clearcut conditions is not warranted. Our simulations reveal that increasing the number of planting heads per crane arm rather than number of crane arms per base machine offers the greatest potential to raise the productivity of intermittently advancing planting machines.
  • Ersson,  Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, SE-901 83 Umeå, Sweden ORCID ID:E-mail: back.tomas.ersson@slu.se (email)
  • Jundén,  UMIT Research Lab, Umeå University, SE-901 87 Umeå, Sweden ORCID ID:E-mail: linus.junden@gmail.com
  • Bergsten,  Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, SE-901 83 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
  • Servin,  UMIT Research Lab, Umeå University, SE-901 87 Umeå, Sweden ORCID ID:E-mail: martin.servin@physics.umu.se
article id 108, category Research article
Back Tomas Ersson, Urban Bergsten, Ola Lindroos. (2011). The cost-efficiency of seedling packaging specifically designed for tree planting machines. Silva Fennica vol. 45 no. 3 article id 108. https://doi.org/10.14214/sf.108
Today’s crane-mounted planting heads plant seedlings with biologically similar or better results than operational manual planting. However, the total cost of mechanized tree planting in southern Sweden must decrease at least 25% to compete economically with manual planting. Although seedlings packed in machine-specific packaging increase the productivity of planting machines by reducing seedling reloading time, they also increase logistics and investment costs. In this study, we analyzed the total cost of outplanting seedlings with an excavator-mounted Bracke Planter and seedlings packed according to four different concepts: cultivation trays, cardboard boxes, band-mounted seedlings in cardboard boxes and linked pots in container modules. The total cost per planted seedling was calculated for each packaging system as the sum of all costs from nursery to the recovery of empty packaging. The results showed that today’s system of transporting seedlings in cultivation trays is the most cost-efficient of the four alternatives. Machine-specific seedling packaging was 16–23% costlier per planted seedling than cultivation trays when trucking distances were 100 km. Sensitivity analyses indicated that machine-specific seedling packaging increased in cost-efficiency relative to cultivation trays primarily when more planting machines were contracted, but also as planting machine fixed costs and productivity increased. Moreover, the relative cost-efficiency of band-mounted seedlings, but not seedlings in container modules, increased with increasing trucking distance. Thus, we show that investments in machine-specific seedling packaging for today’s planting machines are justified only when the fixed costs, productivity and number of contracted planting machines increase substantially.
  • Ersson, Swedish University of Agricultural Sciences, Department of Forest Resource Management, SE-90183 Umeå, Sweden ORCID ID:E-mail: back.tomas.ersson@slu.se (email)
  • Bergsten, Swedish University of Agricultural Sciences, Department of Forest Resource Management, SE-90183 Umeå, Sweden ORCID ID:E-mail:
  • Lindroos, Swedish University of Agricultural Sciences, Department of Forest Resource Management, SE-90183 Umeå, Sweden ORCID ID:E-mail:
article id 134, category Research article
Dan Bergström, Urban Bergsten, Tomas Nordfjell. (2010). Comparison of boom-corridor thinning and thinning from below harvesting methods in young dense Scots pine stands. Silva Fennica vol. 44 no. 4 article id 134. https://doi.org/10.14214/sf.134
At present, only a small proportion of the potential extractable bioenergy from young dense forests in Sweden is utilized. The conventional mechanized first thinning systems used in such stands suffer from low productivity, so the operation is only profitable in stands with bigger trees and high standing volumes. Conventional harvesters are used for this operation equipped with accumulating felling heads designed for handling several trees during each crane cycle. In thinning from below the felling and bunching work requires many time-consuming non-linear crane movements to avoid felling or damaging of future crop trees. However, higher productivity can be achieved when trees between strip roads are harvested in about 1 m-wide corridors with a length corresponding to the reach of the crane. We refer to this operation as boom-corridor thinning. The objective of this study was to compare felling and bunching productivity in young dense stands when employing thinning from below or boom-corridor thinning. Experiments were performed using a randomized block design involving between 4400 and 18 600 trees x ha-1 with a corresponding average tree size of 7.2 and 3.2 cm dbh, respectively. Based on the average tree being removed at a dbh of 5.7 cm, the productivity (ODt x PW-hour-1) was significant (almost 16%) higher for the boom-corridor thinning than for thinning from below treatment. At the same time, the time taken for the work element “Crane in-between” (the period between the loaded crane starting to move towards a tree and the felling head rapidly slowing down for positioning) was significantly reduced, by almost 17%. The positive results were achieved even though the operator was new to the method. To achieve a significantly higher efficiency during the felling and bunching operation, development of new harvesting equipment and operating techniques seems crucial.
  • Bergström, Swedish University of Agricultural Sciences, Dept of Forest Resource Management, Section of Planning and Operations Management, Umeå, Sweden ORCID ID:E-mail: dan.bergstrom@srh.slu.se (email)
  • Bergsten, Swedish University of Agricultural Sciences, Dept of Forest Resource Management, Section of Planning and Operations Management, Umeå, Sweden ORCID ID:E-mail:
  • Nordfjell, Swedish University of Agricultural Sciences, Dept of Forest Resource Management, Section of Planning and Operations Management, Umeå, Sweden ORCID ID:E-mail:
article id 214, category Research article
Michelle de Chantal, Hannu Rita, Urban Bergsten, Mikaell Ottosson Löfvenius, Harald Grip. (2009). Frost heaving of Picea abies seedlings as influenced by soil preparation, planting technique, and location along gap-shelterwood gradients. Silva Fennica vol. 43 no. 1 article id 214. https://doi.org/10.14214/sf.214
The effects of soil preparation, planting technique and location along gap-shelterwood gradients (position and orientation) on frost heaving damage to seedlings were studied in Vindeln Experimental Forests, northern Sweden. The forest was harvested in a grid pattern in winter 2004–2005, forming gaps and shelterwood areas of 30 x 40 m each. Gap-shelterwood gradients were delimited in four orientations and subdivided into five positions: 7 m and 15 m into the gap and shelterwood, and at the gap edge. At each position, three replicates of three soil preparations were made: exposed E and B horizons and HuMinMix (milled vegetation and humus layers mixed with surface mineral soil). In early October 2005, one-year-old containerized Picea abies (L.) Karst. seedlings were planted using four techniques: normal and deep planting, and mobile and fixed experimental containers. After one winter, frost heaving damage was highest for seedlings on B horizon combined with the mobile container (51 ± 6%) and normal planting (43±6%). Normal- or deep-planted seedlings in HuMinMix had the least damage (5–6.6 ± 2.5%). Compared to normal planting, deep planting reduced frost heaving damage only on B horizon. When considering the orientation, seedlings in the experimental containers had more or similar frost heaving damage than normal- or deep-planted seedlings. Along the eastern gradient, seedlings incurred more frost heaving damage in the center of the gap than under the canopy.
  • Chantal, University of Helsinki, Dept of Forest Ecology & Dept of Forest Resource Management, Helsinki, Finland ORCID ID:E-mail: michelle.dechantal@helsinki.fi (email)
  • Rita, University of Helsinki, Dept of Forest Ecology & Dept of Forest Resource Management, Helsinki, Finland ORCID ID:E-mail:
  • Bergsten, Swedish University of Agricultural Sciences, Dept of Forest Ecology and Management, Umeå, Sweden ORCID ID:E-mail:
  • Löfvenius, Swedish University of Agricultural Sciences, Dept of Forest Ecology and Management, Umeå, Sweden ORCID ID:E-mail:
  • Grip, Swedish University of Agricultural Sciences, Dept of Forest Ecology and Management, Umeå, Sweden ORCID ID:E-mail:
article id 273, category Research article
Stefan Mattson, Urban Bergsten, Tommy Mörling. (2007). Pinus contorta growth in boreal Sweden as affected by combined lupin treatment and soil scarification. Silva Fennica vol. 41 no. 4 article id 273. https://doi.org/10.14214/sf.273
Effects of combining lupin (Lupinus nootkatensis L.) establishment and soil scarification on stem volume and stem biomass yield of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were studied on a poor boreal site in Sweden 18 years after plantation. A field randomized block experiment was established with three different scarification techniques (disc trenching, moulding and ploughing) followed by establishment of lupins by either seeds or roots. There were three blocks without and two blocks with lupins. Overall, on average for the three soil scarification techniques, the lupin treatment significantly increased the volume per hectare by 102%.The lupin treatment significantly increased the stem volume per hectare by 236% for mounding and 139% for disc trenching, whereas the 55% increase for ploughing was not significant. The increase in the total stem biomass yield per tree was more pronounced for larger trees; 46% for average trees and 106% for dominant trees. However, there were no significant differences between scarification techniques for the lupin treatment in total stem biomass yield. Over the 18-year period, the increased growth rate following the lupin treatment resulted in a significantly decreased average stem basic wood density (on average 6%) for the sample trees. Because lupin is a nitrogen-fixing plant species, the large increase in tree growth following the lupin treatment was probably an effect of increased amount of nitrogen in the soil. The results indicate that use of lupin is a possible alternative to increase site productivity of lodgepole pine on poor boreal sites.
  • Mattson, Swedish University of Agricultural Sciences, Dept of Forest Ecology and Management, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Bergsten, Swedish University of Agricultural Sciences, Dept of Forest Ecology and Management, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Mörling, Swedish University of Agricultural Sciences, Dept of Forest Ecology and Management, SE-901 83 Umeå, Sweden ORCID ID:E-mail: tommy.morling@ssko.slu.se (email)
article id 298, category Research article
Ulfstand Wennström, Urban Bergsten, Jan-Erik Nilsson. (2007). Seedling establishment and growth after direct seeding with Pinus sylvestris: effects of seed type, seed origin, and seeding year. Silva Fennica vol. 41 no. 2 article id 298. https://doi.org/10.14214/sf.298
The early effects of seed type, seed origin, and seeding year on seedling emergence, survival, and growth after one to four years was quantified and examined. Two experimental series of Scots pine located at 61°N and 64°N and six orchard seed lots and six stand seed lots of adequate geographical origins in each series were used. Both series were replicated at five sites for up to five years. On average, orchard seed lots had 16% and 12% higher seedling emergence, in relation to sown germinable seeds, than stand seed lots in the northern and southern series. The survival from year 1 to year 4 was also higher for orchard seedlings than for stand seedlings; there was a 77% and 72% survival rate in the northern series and a 58% and 49% survival rate in the southern series for orchard and stand seedlings respectively. On average, after four years orchard seedlings were 26% taller in the northern series and 13% taller in the southern series. The gain in height growth for the orchard seeds was positive at all seeding years, at all sites, and at all seedling ages. If survival was calculated to the height of a four-year-old seedling, the survival of orchard seedlings increased by 3% in the northern and 1% in the southern series as the result of the higher growth of orchard seedlings. Using orchard seeds resulted in 6 percent units higher growth gain when the clear cuts were regenerated with direct seeding than with plants using the same seed material. Changes in the ranking of seed lots and seed types at different sites and seeding years for seedling emergence is an effect of external factors such as grazing and foraging that cannot be related directly to the tested factors.
  • Wennström, Skogforsk, Box 3, SE-918 21 Sävar, Sweden ORCID ID:E-mail: ulfstand.wennstrom@skogforsk.se (email)
  • Bergsten, SLU, Dept. of Forest Ecology and Management, SE-901 83 Umeå, Sweden & SLU, Vindeln Experimental Forest, SE-922 91 Vindeln, Sweden ORCID ID:E-mail:
  • Nilsson, SLU, Dept. of Forest Genetics and Plant Physiology ORCID ID:E-mail:
article id 296, category Research article
Samuel Roturier, Sofia Bäcklund, Maria Sundén, Urban Bergsten. (2007). Influence of ground substrate on establishment of reindeer lichen after artificial dispersal. Silva Fennica vol. 41 no. 2 article id 296. https://doi.org/10.14214/sf.296
Methods to improve the recovery of reindeer lichen after soil disturbance or overgrazing are being sought for areas where reindeer are herded. The effects of four substrates – mineral soil, moss, twigs and pine bark – on the establishment of lichen fragments after total removal of the vegetation were thus studied in a middle-aged pine stand and a clear-cut, both located in a lichen-rich pine-heath. Cladina mitis fragments of two sizes were manually dispersed in 1 m2 quadrats and their movements from their respective dispersal points were registered after one year. The natural re-establishment of lichens in the quadrats was monitored over three years by using digital pictures. In the forest stand, no significant differences were detected in either the fragment movement or the lichen establishment between the different substrates, but the fragment size had positive effects on both parameters. In the clear-cut, the moss substrate was the most suitable not only for the artificially dispersed lichens to fasten to, but also for the natural settlement of lichens from the surrounding lichen mat. More lichen thalli fastened to the bark and twigs substrates than to the mineral soil, but the settlement of lichens from the surrounding was greater on bare mineral soil substrate. The results indicate that artificial dispersal of lichen thalli on an appropriate substrate could be a successful strategy for promoting lichen recovery.
  • Roturier, SLU, Vindeln Experimental Forests, Svartberget Fältstation, SE-922 91 Vindeln, Sweden ORCID ID:E-mail: samuel.roturier@esf.slu.se (email)
  • Bäcklund, ORCID ID:E-mail:
  • Sundén, ORCID ID:E-mail:
  • Bergsten, SLU, Dept of Forest Ecology, SE-901 83 Umeå, Sweden ORCID ID:E-mail:

Category: Research note

article id 1136, category Research note
Håkan Lideskog, Back Tomas Ersson, Urban Bergsten, Magnus Karlberg. (2014). Determining boreal clearcut object properties and characteristics for identification purposes. Silva Fennica vol. 48 no. 3 article id 1136. https://doi.org/10.14214/sf.1136
Highlights: We define the quantitative properties and qualitative characteristics of stumps, stones, slash, and roots, the most important objects interacting with machine activities after clearcutting; We develop a flowchart showing how a computer-aided system using clearcut object identification should be executed.
After clearcutting, machines traffic the clearcut conducting different silvicultural activities. Many objects on a forest clearcut (slash residues, stones, stumps and roots) may disturb e.g. site preparation and planting. This paper describes properties and characteristics of these objects. A flowchart was developed that describes a possible computer-aided system that identifies the objects, and ultimately, makes a machine avoid or target them. A system for obstacle identification creates conditions for further technical development and (semi)automation of e.g., site preparation, mechanized planting, and stump removal.
  • Lideskog, Division of Product and Production Development, Luleå University of Technology, SE-97187 Luleå, Sweden ORCID ID:E-mail: hakan.lideskog@ltu.se (email)
  • Ersson, Department of Forest Biomaterials and Technology, SLU, SE-90183 Umeå, Sweden ORCID ID:E-mail: back.tomas.ersson@slu.se
  • Bergsten, Department of Forest Biomaterials and Technology, SLU, SE-90183 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
  • Karlberg, Division of Product and Production Development, Luleå University of Technology, SE-97187 Luleå, Sweden ORCID ID:E-mail: magnus.karlberg@ltu.se
article id 1017, category Research note
Jeanette Edlund, Urban Bergsten, Hans Arvidsson. (2013). A forest machine bogie with a bearing capacity dependent contact area: acceleration and angular orientation when passing obstacles and drawbar pull force and free rolling resistance on firm ground. Silva Fennica vol. 47 no. 3 article id 1017. https://doi.org/10.14214/sf.1017
Highlights: The Long Tracked Bogie principle (LTB) has low contact area on firm ground with low load, it increases when higher traction force is needed and on softer soil; Free rolling resistance on firm ground was 60% of the value for a conventional bogie; LTB appears to pass wider ditches/cavities, more smoothly with lower pitch angle, than a conventional bogie.
The Long Tracked Bogie with contact area dependent on bearing capacity was compared to a conventional bogie. Two unloaded Vimek 608 forwarders with different bogies and with the traction from the front wheel removed were compared. Two high obstacles, 0.1 and 0.2 m high, respectively and 0.15 m in width, and two deep obstacles/ditches with a depth of 0.2 m and a width 1 and 1.5 m were used for tests. Towing tests on flat ground were done by connecting the machines to each other with a load cell in between.  There were no or small differences in acceleration when passing obstacles between the two types of bogie. LTB passed wider ditches/cavities with lower pitch angles (one bogie/side passing) and 0.2 m obstacles with higher roll angles than a conventional bogie. On firm ground, free rolling resistance of the LTB was about 60% of the resistance of the conventional bogie. The drawbar pull force for the LTB was indicated to be a few percentage units higher than for the conventional bogie when it was driving with a towed machine acting as a braking force. The LTB principle might yield opportunities to improve the way we construct bogies for forest machines. Even if the contact area is low on firm ground when the machine is running with low load, it increases when higher traction force is needed and on softer soil. Further field tests are needed to evaluate the LTB when used on soft ground and with higher load as well.
  • Edlund, Sveaskog AB, SE-941 86 Piteå, Sweden ORCID ID:E-mail: jeanette.edlund@sveaskog.se
  • Bergsten, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se (email)
  • Arvidsson, SMP Umeå, SE-904 03 Umeå, Sweden ORCID ID:E-mail: hans.arvidsson@smp.sp.se
article id 974, category Research note
Kristina Ahnlund Ulvcrona, Lars Karlsson, Ingegerd Backlund, Urban Bergsten. (2013). Comparison of silvicultural regimes of lodgepole pine (Pinus contorta) in Sweden 5 years after precommercial thinning. Silva Fennica vol. 47 no. 3 article id 974. https://doi.org/10.14214/sf.974
Highlights: Management regimes can serve different purposes such as biomass production, pulp and timber production or a combination of those; 30 tons biomass or 38–45 m3 stem volume ha–1 could be derived by schematic corridor thinning (70%) at year 20; Producing large amounts of biomass early in the rotation period does not exclude a conversion into pulp and timber production.
Early effects (stem volume, mean diameter at breast height weighted against basal area (Dgv) (Dgv), biomass and damage frequency) of different silvicultural regimes 18-19 years after direct seeding of lodgepole pine in northern Sweden were analysed. A Conventional regime, (i) precommercial thinning (PCT) to 2200 stems ha-1, was compared to: (ii) High biomass production (15 300 stems ha-1, no PCT) with and without corridor thinning at year 20, (iii) production of Large dimension trees (PCT to 1700 stems ha-1), (iv), Combined high biomass production and production of conventional round wood (PCT to 4500 stems ha-1). PCT was done 15 yrs after direct seeding for all PCT treatments. Local biomass functions showed that the regimes aiming at High biomass production displayed ca 144-157% more biomass and 134-143% more stem volume than the Conventional and Large dimension regimes (ca 21 tons and 31 m3 ha-1). Dgv for the 1000 (9.2 cm) and 2000 (8.3 cm) largest trees ha-1 appeared unaffected by regime. By schematic corridor thinning (70% of the total area) at year 20 in the High biomass regime, 27-32 tons of biomass ha-1 and 38-45 m3 ha-1 could be derived while still having a Dgv of the 1000 largest trees ha-1 of about 8 cm. Therefore, this study indicates that it is possible to produce and harvest large amounts of biomass and stem volume early in the rotation period without excluding later pulp and timber production. This initial regime comparison should be continued over time.
  • Ahnlund Ulvcrona, SLU, Forest Biomaterials and Technology, Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: kristina.ulvcrona@slu.se (email)
  • Karlsson, SLU, Forest Biomaterials and Technology, Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: lars.karlsson@slu.se
  • Backlund, SLU, Forest Biomaterials and Technology, Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: ingegerd.backlund@slu.se
  • Bergsten, SLU, Forest Biomaterials and Technology, Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
article id 914, category Research note
Ingegerd Backlund, Urban Bergsten. (2012). Biomass production of dense direct-seeded lodgepole pine (Pinus contorta) at short rotation periods. Silva Fennica vol. 46 no. 4 article id 914. https://doi.org/10.14214/sf.914
Lodgepole pine (Pinus contorta) is a fast-growing species that is suitable for producing woody biomass in Nordic countries. Direct seeding of this species is cheaper than planting and creates dense, stable stands. The objective of this study was to quantify the stem volume and biomass production of direct seeded lodgepole pine stands grown under different site conditions with different stem densities, at an age that would permit extensive harvesting of biomass. A circle-plot inventory was performed in 16 of the oldest direct seeded lodgepole pine stands in mid-northern Sweden. Stemwood production of almost 200 m3/ha was achieved on average on the best sites, rising to about 300 m3/ha for the best circle-plots within 30 years of direct seeding despite the fact that pre-commercial thinning was made once or twice. This corresponds to 100 and 140 tons of dry weight biomass/ha, respectively. Higher stand stem densities (≥3000 st/ha) yielded more biomass with only slight reductions in diameter at breast height. The development of stem volume with respect to dominant height in direct seeded stands was becoming comparable to that in planted stands with similar spacing. It therefore seems that there is an unutilized potential for cost-effectively growing lodgepole pine in dense stands for biomass production after direct seeding. It may be possible to devise regimes for short(er) rotation forestry that would yield substantial amount of inexpensive biomass for biorefineries within a few decades.
  • Backlund, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: ingegerd.backlund@slu.se (email)
  • Bergsten, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd, SE-901 83 Umeå, Sweden ORCID ID:E-mail: urban.bergsten@slu.se
article id 311, category Research note
Dan Bergström, Urban Bergsten, Tomas Nordfjell, Tomas Lundmark. (2007). Simulation of geometric thinning systems and their time requirements for young forests. Silva Fennica vol. 41 no. 1 article id 311. https://doi.org/10.14214/sf.311
In Fennoscandia, large areas that have not been subjected to pre-commercial thinning (PCT), and thus support dense stands, are becoming suitable for harvesting biomass. However, efficient systems for harvesting biomass from young stands have not yet been developed. In order to optimise biomass harvesting it is here hypothesized that the handling unit should not be a single tree but a corridor area, i.e., all trees in a specific area should be harvested in the same crane movement cycle. Three types of corridor harvesting approaches (using accumulating felling heads for geometric harvesting in two different patterns) were compared in terms of time required to fell a corridor of standardised size. Corridors are defined as strips of harvested areas between conventional strip-roads. Harvests were simulated in two types of stands, first thinning (FT) and delayed PCT stands, in which the spatial positions of the trees had been mapped. The differences in simulated time consumption per corridor were minor when the only variable changed was the corridor pattern. However, there were ca. 2-fold and 3-fold differences in simulated time consumption per corridor between the harvesting approaches for the FT stand and the PCT-stand, respectively. Furthermore, area handling (felling head accumulating all trees corridor-wise, with no restrictions on the accumulated number of trees except for a certain load limit) was found to give up to 2.4-fold increases in productivity compared to a single-tree (reference) approach for the FT stand. In conclusion, the simulation results clearly show the benefits of applying area-harvesting systems in young, dense stands.
  • Bergström, SLU, Dept. of Forest Resource Management, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Bergsten, SLU, Dept. of Forest Ecology and Management, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Nordfjell, SLU, Dept. of Forest Resource Management, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Lundmark, SLU, Vindeln Experimental Forests, Svartberget Field Station, SE-922 91 Vindeln, Sweden ORCID ID:E-mail:
article id 325, category Research note
Daniel Eriksson, Henrik Lindberg, Urban Bergsten. (2006). Influence of silvicultural regime on wood structure characteristics and mechanical properties of clear wood in Pinus sylvestris. Silva Fennica vol. 40 no. 4 article id 325. https://doi.org/10.14214/sf.325
The objective of the study presented here was to evaluate the influence of two contrasting silvicultural regimes on the structural characteristics and mechanical properties of different wood tissue types at different heights in Scots pine (Pinus sylvestris L.) trees, and reasons for these differences. Wood samples were taken from two stands (a dense 85-year-old stand established by direct seeding and a 56-year-old widely spaced stand established by planting, designated SDR and PWR, respectively in the boreal zone of Sweden). The wood properties associated with the examined silvicultural regimes differed, in terms of both structural characteristics (with up to fivefold differences between SDR and PWR) and mechanical properties (with up to almost threefold differences between SDR and PWR). Differences between the regimes were highest for stiffness, followed by strength and hardness properties and lowest for relative stiffness after 1000 h of loading (creep) (with higher parameter values for SDR than for PWR in each case). The rankings could be explained by differences among the mechanical properties in their sensitivity to maturation of wood characteristics. In conclusion, silvicultural regimes have great potential to regulate wood structural characteristics and mechanical properties, apparently due to the influences of the green crown and growth rate on the vascular cambium, the strength of which vary throughout the rotation period. A silvicultural regime could therefore be seen as a tool that can be used to select material qualities and to make wood a more homogenous material for engineers.
  • Eriksson, Swedish University of Agricultural Sciences, Vindeln Experimental Forest, Svartberget Fieldstation, SE-922 91 Vindeln, Sweden ORCID ID:E-mail: daniel.eriksson@esf.slu.se (email)
  • Lindberg, Luleå University of Technology, Division of Polymer Engineering, SE-971 87 Luleå, Sweden ORCID ID:E-mail:
  • Bergsten, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:

Category: Article

article id 5364, category Article
Urban Bergsten. (1988). Invigoration and IDS-sedimentation of Pinus sylvestris seeds from northern Finland. Silva Fennica vol. 22 no. 4 article id 5364. https://doi.org/10.14214/sf.a15521

In Northern Finland as well as in Northern Sweden there is a shortage of high-quality Scots pine (Pinus sylvestris L.) seeds, mostly due to unsuitable temperatures during the development and maturation of cones and seeds. Methods have been developed for elimination of non-productive seeds and for invigoration of seeds. In the present work, these methods were tested on poorly developed seed lot from Rovaniemi, Northern Finland (66°15’–66°30’; 180 m a.s.l.). The seeds were conditioned using the following treatments:

1. PREVAC method (5 min, 97 kPa below atmospheric pressures) for removal of mechanically damaged seeds (7%)

2. Invigoration using incubation at controlled moisture content (30% f.w) and continuous air supply, for 14 days at 5°C.

3. Additional water supply for 16 hours at 5°C.

4. Drying in dehumidified air until a near maximum difference in density between viable and dead seeds was obtained

5. Separation in a sedimentation flume to achieve a gradient of fractions of different germination rate and capacity.

The treatments resulted in an improvement of germination percentage from 33 to about 95% and a reduction in mean germination time from 8.8 days to 6 days if the control and the best fractions (32% seeds) were compared.

  • Bergsten, ORCID ID:E-mail:

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