Comparison of energy-wood and pulpwood thinning systems in young birch stands

In early thinnings, a profitable alternative to pulpwood could be to harvest whole trees as energy-wood. In theoretical analyses, we compared the extractible volumes of energy-wood and pulpwood, and their respective gross values in differently aged stands of early birch thinnings at varying intensities of removal. In a parallel field experiment, we compared the productivity at harvest of either pulpwood or energy-wood, and the profitability when the costs of harvesting and forwarding were included. The theoretical analyses showed that the proportion of the total tree biomass removed as pulpwood increased with increasing thinning intensity and stem size. The biomass volume was 1.5–1.7 times larger than the pulpwood volume for a 13.9 diameter at breast height stand and 2.0–3.5 times larger for a 10.4 diameter at breast height stand. In the field experiment, the harvested volume per hectare of energy-wood was almost twice as high as the harvest of pulpwood. The harvesting productivity (trees Productive harvesting Work Time-hour−1) was 205 in the energy-wood and 120 in the pulpwood treatment. The pulpwood treatment generated a net loss, whereas the energy-wood treatment generated a net income, the average difference being €595 ha−1. We conclude that in birch-dominated early thinning stands, at current market prices, harvesting energy-wood is more profitable than harvesting pulpwood

Dålig beredskap för stormar

I vanliga fall är man som svensk och verksam inom det skogstekniska området van att kunskapscentrum rörande avverkningsteknik är just i Sverige, eller Finland. Den stora storm som koncentrerat drabbade delar av södra Sveriges skogar var dock inget vanligt fall. De erfarenheter som vi fick i samband med stormfällningarna på slutet av 60-talet är antingen till stor del glömda eller av mindre värde då både teknik och organisation är förändrad. Men det finns i närbelägna länder en färsk, stor, och dyrköpt kunskapsbank rörande stormfälld skog. I december 1999 blåste stormarna Martin och Lothar ner 180 millioner m3 skog i Europa, varav minst 115 millioner m3 i Frankrike (nästan 3 årsavverkningar). Liksom i Sverige nu inträffade i Frankrike då att en del fick psykologiska problem och depressioner till följd av förödelsen. Tyskland, Schweiz och Danmark drabbades också. Uppskattningsvis 5 millioner m3 blåste även ner i södra Sverige. Som en följd av dessa stormskador genomfördes ett EU-finansierat 3-årigt forsknings- och informationsprojekt ”Storm damaged forests – STODAFOR”, med deltagare från 10 länder och 16 organisationer, dock ingen från Sverige eller Finland. STODAFORs avslutande konferens gick av stapeln 27-28 oktober 2004 i Frieburg, Tyskland. Av de 62 registrerade deltagarna kom ingen från Sverige, men 2 från Finland. I Danmark, liksom i många andra av de drabbade länderna, bedrevs nationell forskning. Denna artikel bygger i huvudsak på information från projektet STODAFOR, samt Danska sammanställningar av erfarenheter. För mer detaljerade kunskaper hänvisas till STODAFORs fritt tillgängliga hemsida (http://www.ctba.fr/stodafor/index.htm) och ”Videntjänsten” på Skov & Lanskab ([email protected])

Productivity of a prototype truck-mounted logging residue bundler and a road-side bundling system

When recovering logging residues (LR) for bioenergy its density should be increased before road transport, otherwise a low proportion of the trucks’ load capacity will be used. One way this can be currently done is to compress LR into bundles that are forwarded to roadside landing. A less well-developed alternative is to forward loose LR and bundle it at landing. In the presented study, a prototype specifically developed for road-side bundling was found to produce larger, heavier bundles than bundling machinery intended for in-field use (mean length, diameter and raw bulk density 4.7 m, 0.8 m and 285 kg m–3, respectively, with 299–445 kg oven dry matter per bundle). The machine was a so at least 30% more productive than previously described in-field bundling systems, producing 14–19 bundles per productive work hour (PWh), equivalent to 5.2–7.8 oven-dry tonnes PWh–1. Bundles were estimated to use 67–86% of an LR truck’s 30 tonnes load capacity, similar to proportions used when transporting loose LR. However, a continuous feeding and compressing process would probably almost double productivity, while longer bundles would enable full use of truck load capacity. With such improvements bundling at road-side could provide a viable alternative to current LR-recovering systems

Skörd av övergrov salix med skogsbrukets maskiner

Om en salixodling innehåller stammar med en diameter i stubbhöjd (dsh) grövre än 5-7 cm får konventionella direktflisande skördemaskiner tekniska problem. I dagsläget finns det i Sverige arealer med salix som växt sig övergrov. I dessa odlingar kan skörd med skogsmaskiner vara ett alternativ. Syftet med denna studie var att mäta produktiviteten på konventionella skogsmaskinsystem, anpassade för skörd av ”klena” stammar i gallringsskog, vid skörd av övergrov salix, samt att jämföra dessa systems kostnadseffektivitet mot konventionella system för salixskörd. Ett skördare-skotaresystem och ett en-maskinsystem (drivare) studerades vid skörd av normal och övergrov salix. Det normala området innehöll 36 ton torrsubstans (TS) per ha, en diameter i stubbhöjd (dsh) i medeltal och maximalt på 2,7 cm respektive 6,1 cm. Det övergrova området innehöll 56 ton TS/ha, en dsh i medeltal på 3,1 cm respektive 10,0 cm. Jämförande systemanalyser utfördes mot både konventionella och teoretiska salixskördesystem (baserades på litteraturdata) i normal, övergrov och mer övergrov (75 ton TS/ha) salix. Fältstudien visade att typ av odling hade störst effekt på skördarens produktivitet (tonTS/timme) vilken i medeltal blev 56% högre i det övergrova området jämfört mot det normala. Produktiviteten på skotaren påverkas främst av skotningsavståndet. Drivaren hade låg produktivitet som dock ökade med 36% i den övergrova odlingen. Drivaren påverkas också kraftigt av skotningsavståndet. Systemanalysen visade att skördare-skotaresystemet gav ett positivt netto i alla typodlingar, men att drivaresystemet gav ett negativt netto i alla typodlingar. Analysen visar tydligt att konventionella system för salixskörd blir mer kostnadseffektiva i alla typodlingar än skogsmaskinsystemen. Salixdirektflisningssystemet gav högst netto i det normala och övergrova området. Ett teoretiskt salixbuntskördaresystem gav högst netto i det mer övergrova området. Trenden är att systemet med salixdirektflisning och ett teoretiskt system med salixhelstamskörd och direktlastning minskar i kostnadseffektivitet med ökad biomassa/ha, men att skogsmaskinsystemen och salixbuntskördaresystemet ökar i kostnadseffektivitet med ökad biomassa/ha. Skogsmaskiner är i dagsläget inte ett kostnadseffektivt val vid skörd av salix, och kommer förmodligen aldrig att bli det heller. Dock utgör skogsmaskiner ett robust alternativ som alltid fungerar oavsett hur gamla och övergrova salixodlingar har blivit

Distribution, characteristics and potential of biomass-dense thinning forests in Sweden

Understanding the characteristics of unutilized biomass resources, such as small-diameter trees from biomass-dense thinning forests (BDTF) (non-commercially-thinned forests), can provide important information for developing a bio-based economy. The aim of this study was to describe the areal distribution, characteristics (biomass of growing stock, tree height, etc.) and harvesting potential of BDTF in Sweden. A national forest inventory plot dataset was imported into a geographical information system and plots containing BDTF were selected by applying increasingly stringent constraints. Results show that, depending on the constraints applied, BDTF covers 9-44% (2.1-9.8 M ha) of the productive forest land area, and contains 7-34% of the total growing stock (119-564 M OD t), with an average biomass density of 57 OD t ha^-1. Of the total BDTF area, 65% is located in northern Sweden and 2% corresponds to set-aside farmlands. Comparisons with a study from 2008 indicate that BDTF area has increased by at least 4% (about 102 000 ha), in line with general trends for Sweden and Europe. Analyses revealed that the technical harvesting potential of delimbed stemwood (over bark, including tops) from BDTF ranges from 3.0 to 6.1 M OD t yr^-1 (7.5 to 15.1 M m^3 yr^-1), while the potential of whole-tree harvesting ranges from 4.3 to 8.7 M OD t yr^-1 (10.2 to 20.6 M m3 yr^-1) depending on the scenario considered. However, further technological developments of the harvest and supply systems are needed to utilize the full potential of BDTF

Operational Aspects of Row and Selective Thinning in the Establishing of a Shelterwood in a 50-Year-Old Norway Spruce Stand

The aim of this study is to investigate the productivity, thinning quotient, reduction in basal area, damage rate, and costs of operation of row and selective thinning in the establishment of a shelterwood in a medium-aged Norway spruce stand. The cutting was performed with a single-grip harvester operating from existing striproads (spacing 15 m) parallel to the tree-rows. Extraction with a forwarder was studied in the same stand. The two thinnings were more alike than expected. The thinning quotient was 0.9 and the reduction in basal area round 40% in both treatments. The time consumption for harvesting was larger in row than in selective thinning because row thinning was more difficult to perform when the harvester worked from striproads parallel to the tree-rows. No difference in forwarding productivity was found. The damage rate was higher in row than in selective thinning. It is concluded that row thinning from striproads parallel to the tree-rows has a negative influence on both productivity and quality of the work. This type of row thinning is difficult to perform because the tree-rows are difficult to identify and because the trees are more difficult to reach. The operational aspects should be considered before a thinning method is chosen. Row thinning should preferably be carried out either by driving on removed rows or from striproads perpendicular to the tree-rows

Effects of Boom-Corridor and Selective Thinnings on Harvester Productivity in Dense Small Diameter Pyrenean Oak (Quercus pyrenaica Willd.) Coppices in Spain

Due to socioeconomic transformations in the 20th century, Quercus pyrenaica Willd. coppices in Spain, as well as other European coppices, have experimented an abandonment and lack of intervention leading to stagnant high density stands with fragile health due to competition. Thinnings are often required to ensure their stability and health, producing forest products such as firewood or biomass, which are key energy sources in a carbon-neutral economy. However, thinnings are seldom performed because they lack economic sustainability due to a low productivity, high costs and low biomass prices. In this study, two thin-ning methods, selective thinning (ST) and boom-corridor thinning (BCT), were tested car-rying out a time study in a high-density small-diameter Q. pyrenaica stand in the Leon province (Castilla y Leon, Spain) with a forest harvester base machine, on which an accumulating felling head Bracke C16c was mounted. The residual stands were significantly different regarding the final density (greater in BCT) and the final average DBH (bigger in ST), while thinning intensity (odt center dot ha-1) was the same. In most work elements, time per tree was not significantly different. BCT showed a significant 48.6% increase in harvester productivity when compared to ST, with averaging 4.43 and 2.99 odt center dot pmh-1, respectively, due mainly to the average weight per extracted tree, 42% greater in BCT. When considering the common range of unit tree weight, the productivity was 16-23% greater for BCT, far less than observed in the trials. These results show the potential of BCT over ST in the studied conditions, although there is room for improvement. Further studies could include the future evolution of the treated stands and perform a cost analysis

How stem size variations in forest stands influence harvester productivity and the use of productivity models

Stem size has the greatest effect on harvester productivity, and stem sizes vary in a forest stand. How these within-stand variations influence harvester productivity is normally not considered in studies or predictions of productivity. This study suggests reasons as to why the current production and/or application of productivity models are prone to bias from stem size variations in a stand, irrespective of whether models were developed from tree-based or stand-based studies. Moreover, it also provides empirical data on the stand stem size variation's influence on stand-based modeling of harvester productivity. Data from 11 harvesters in 347 final fellings and four harvesters in 80 thinnings were used. The mean productivity was 26.7 and 11.0 m(3)/PMh(5) in final felling and thinning, respectively, and the mean stem size explained most of the observed variation. The productivity in final felling decreased with increased levels of stand stem size variation, as well as with increases in the proportion of broadleaf trees in the stand. For thinnings, productivity increased with increases in the proportion of pine trees in the stand, but there was no significant effect of stand stem size variation or other tested factors. The results show that stand stem size variation is a relevant factor to consider when modeling and predicting harvester productivity