Spruce and Pine on Drained Peatlands Wood Quality
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HELSINGIN YLIOPISTON METSÄVAROJEN KÄYTÖN LAITOKSEN JULKAISUJA 35 UNIVERSITY OF HELSINKI DEPARTMENT OF FOREST RESOURCE MANAGEMENT PUBLICATIONS 35 SPRUCE AND PINE ON DRAINED PEATLANDS WOOD QUALITY AND SUITABILITY FOR THE SAWMILL INDUSTRY Juha Rikala To be presented, with the permission of the Faculty of Agriculture and Forestry of the University of Helsinki, for public critisism in the Auditorium B2, Latokartanonkaari 9 A, Helsinki, on 21 November 2003, at 12 o´clock noon. Helsinki 2003 Opponent: Professor Torbjörn Elowson Department of Forest Products and Markets Swedish University of Agricultural Sciences SE-750 07 Uppsala, Sweden Reviewers: Professor Matti Kärkkäinen Sepetlahdentie 7 A 21 FIN-02230 Espoo, Finland Professor Mats Nylinder Department of Forest Products and Markets Swedish University of Agricultural Sciences SE-750 07 Uppsala, Sweden Supervisor: Professor Marketta Sipi Department of Forest Resource Management FIN-00014 University of Helsinki, Finland Revision of English: Carol Pelli Language Center FIN-00014 University of Helsinki, Finland Cover: Upper left: Mature spruces on Herb-rich type, Jaakkoinsuo, Municipality of Vilppula Upper right: Mature pines on Vaccinium vitis-idaea type, Ruotsinkylä, Municipality of Tuusula Lower left: A felled spruce stem cut into logs. Sample discs were taken for wood property studies. Lower right: Sawn pieces on conveyor, Pori College of Forestry, Municipality of Kullaa (Photos: Juha Rikala) ISBN 951-45-9091-0 (paperback) ISBN 951-45-9092-9 (pdf) ISSN 1236-1313 Helsinki 2003 Yliopistopaino Rikala, J. 2003. Spruce and pine on drained peatlands ʊ wood quality and suitability for the sawmill industry. University of Helsinki, Department of Forest Resource Management, Publications 35. 147 p. ABSTRACT Drained peatlands are a characteristic specific to Finnish forestry. Almost 5 million hectares of peatlands have been drained for wood production, which is exceptional even on a global scale. According to the National Forest Inventories, forest drainage seems to be a major factor in the increased volume growth observed in Finnish forests. To date, only a few studies have focused on the qualitative properties of peatland trees, and thus, knowledge has been insufficient to evaluate the suitability of the wood for various end-uses. This is, however, an essential component in assessing the overall profitability of drainage investments. This study aimed at clarifying the most important external and internal quality properties of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) timber trees growing on drained peatlands. The suitability of raw wood material for sawn timber and its processed products were examined, as were the differences in quality properties between tree stands on drained peatland and mineral soil. The primary hypothesis was that growing conditions typical of peatlands affect the phenotype of trees, and hence, the properties of wood and sawn timber. Study material was collected from two site types of Norway spruce (Herb-rich type, Vaccinium myrtillus type) and two site types of Scots pine (Vaccinium vitis-idaea type, Dwarf-shrub type) in southern Finland. Five sample plots were chosen to represent each site type (total of 20 plots). Part of all counted trees (measured for diameter at breast height) was graded as standing trees. These trees were measured for tree height, diameter at a height of 6 m, height of the living crown, and dead branch height. From each stand, 10 trees were felled for further experiments. The stems were cut into saw logs and the logs were graded according to external quality properties. Merchantable tree tops were cut into 2-m bolts to a minimum diameter of 7 cm. Sample discs were taken from each cut to examine the following wood properties: annual ring width and latewood proportion, heartwood proportion, basic density, and proportion of compression wood. Logs were measured by a logscanner, barked using a barking machine and sawn by blade settings commonly used in the Finnish sawmill industry. Sawn timber was graded before and after drying according to Nordic Timber grading rules. Centre yield was also graded according to the stress grading rules of NS-INSTA 142 and T- grading. Special attention was paid to features affecting quality. Sawn timber was dried to a 20% final moisture content in a warm air kiln at a temperature suitable for size and quality. The changes in timber quality during drying and factors affecting these were studied. Some further experiments were carried out by drying the best quality centre yield sawn timber to a moisture content of 10%. Both in spruce and pine, the stem form characteristics – taper, slenderness, and breast height form factor – were in accordance with those observed in mineral soil sites of corresponding fertility. Various stem form defects, e.g. crooks and sweep, were common in both tree species. In practice, this means that the stems have to be cut into short logs to meet the quality requirements for saw logs. In pine, the relative length of the living crowns was exceptionally low, which was manifested in a long dead branch section. One explanation for this could be 3 the dieback and canker fungus of pines (Gremmeniella abietina) that infected pine stands in southern Finland in the late 1970s and 1980s. Spruces were characteristically thin-branched. The origin of wood material was appearent from the following characteristics. Most trees had a narrow-ringed heart, whereas the wood grown after drainage was wide-ringed. An increase in growth due to drainage meant decrease in basic density and latewood proportion. Especially in spruce, high heartwood proportions were found. The amount of compression wood was surprisingly small, which might indicate that it is not a severe problem in managed, mature stands. On average, all of the studied wood properties were similar to those reported from mineral soil sites, but the variation was large. Although spruce stands in this material were relatively old, root rot was unusual. This may be explained by peat soil conditions, which do not favour the spreading of fungi. Spruce sawn timber was of good quality, decreasing only slightly from butt towards the top of the tree. The quality of sawn timber from pine butt logs was good, but numerous dead and unsound knots lowered the quality of sawn timber from the upper parts of stems. Drying deformations and checking were slight in both tree species in export drying (moisture content 20%), but increased dramatically in joinery drying (moisture content 10%). The main causes were checking and twisting. Based on the results, the quality of sawn timber from peatland spruces corresponds to that produced by mineral soil sites. Thus, peatland spruce sawn timber may be utilized in the same end-use areas as spruce sawn timber in general, i.e. mainly in construction. Peatland pine sawn timber is slightly poorer than that of upland sites. Sawn timber from butt logs is suited for purposes from construction to visible joinery. The primary uses for pine middle logs are construction and end-uses that are to be painted or covered. No suggestions for the use of pine top logs can be given due to inadequate observations. Keywords: drained peatlands, timber trees, external properties, wood properties, quality of sawn timber, Picea abies, Pinus sylvestris 4 CONTENTS ABSTRACT _______________________________________________________________ 3 ABBREVIATIONS AND DEFINITIONS ______________________________________ 7 PREFACE _______________________________________________________________ 11 1 INTRODUCTION _______________________________________________________ 12 1.1 Definitions for Peatland and Peatland Stand ______________________________ 12 1.2 Forest Drainage and Its Role in Wood Production in Finland ________________ 12 1.3 Spruce and Pine as Raw Material for Mechanical Wood Processing___________ 14 1.4 External Tree Properties and Sawmill Industry____________________________ 15 1.5 Wood Properties and Their Role as Indicators of Wood Quality ______________ 17 1.6 Prediction of Quality of Sawn Timber____________________________________ 21 1.7 Hypotheses, Aims, and Scope of the Study ________________________________ 22 2 MATERIALS AND METHODS____________________________________________ 24 2.1 Study Framework ____________________________________________________ 24 2.2 Sample Plots _________________________________________________________ 25 2.2.1 Selection of Sample Plots __________________________________________________________25 2.2.2 Stand and Tree Measurements _______________________________________________________26 2.2.3 Scaling of Felled Sample Trees and Quality Grading of Logs ______________________________28 2.2.4 Determination of Stem Volume ______________________________________________________29 2.3 Wood Property Measurements__________________________________________ 30 2.4 Sawing Experiments __________________________________________________ 33 2.4.1 Stages __________________________________________________________________________33 2.4.2 Measuring of Logs ________________________________________________________________33 2.4.3 Sawing of Logs and Marking of Sawn Timber __________________________________________33 2.4.4 Grading of Sawn Timber ___________________________________________________________34 2.4.5 Drying of Sawn Timber ____________________________________________________________35 2.4.6 Joinery Drying and Ripsawing of Centre Yield__________________________________________35 2.5 Determination of Value of