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Articles by Henrik Heräjärvi
Category: Editorial
article id 10216, category Editorial
(2019). New age of discovery in wood science. Silva Fennica vol. 53 no. 2 article id 10216. https://doi.org/10.14214/sf.10216
- Heräjärvi, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6, FI-80100 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@luke.fi
Category: Research article
article id 10389, category Research article
(2020). Sawlog quality and tree dimensions of Scots pine 34 years after artificial moose browsing damage. Silva Fennica vol. 54 no. 3 article id 10389. https://doi.org/10.14214/sf.10389
Highlights: The first controlled, long-term, experimental study on the tree dimensions and sawlog quality after moose damage; The trees damaged at the seedling stage had a smaller diameter, height, and tree volume at the end of the experiment; The heavier the clipping treatment, the more likely the stem form deteriorated; Deteriorated stem form and vertical branches were the most typical defects.
Moose (Alces alces L.) browsing causes severe damage in Scots pine (Pinus sylvestris L.) seedling stands. The effects of this damage on the quality of sawlogs were studied in a long-term controlled experiment. This article reports the stem size and external quality characteristics of Scots pine stems 34 years after artificial moose browsing damage. Damaging the trees by clipping the main stem at the seedling stage reduced the diameter, height, and tree volume of the trees at the end of the experiment. The tree growth reduction was dependent on the severity of clipping. The differences between the damaged and the control trees were more obvious in diameter than in height at the time of final felling. Stem form defects and vertical branches were the most typical externally detectable defects caused by clipping. Defects in the butt logs were detected in 71–89% of the damaged trees, depending on the clipping treatment severity. The stronger the clipping treatment, the more likely the stem form was defected and the more commonly were vertical branches and crooks detected in the stems. The results indicate that both tree dimensions and stem quality suffer from moose browsing. The findings of this controlled experiment more likely underestimate than overestimate the damage in comparison to real moose browsing. Further analyses are required to assess the effects of browsing damage on the internal quality of sawlogs and subsequent economic outcomes.
- Matala, Natural Resources Institute Finland (Luke), Natural resources, Yliopistokatu 6B, FI-80101 Joensuu, Finland ORCID ID: – E-mail: juho.matala@luke.fi
- Kilpeläinen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Yliopistokatu 6B, FI-80101 Joensuu, Finland ORCID ID: – E-mail: harri.kilpelainen@luke.fi
- Heräjärvi, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6B, FI-80101 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@luke.fi
- Wall, Natural Resources Institute Finland (Luke), Research infrastructure services, Yliopistokatu 6B, FI-80101 Joensuu, Finland ORCID ID: – E-mail: tapio.wall@luke.fi
- Verkasalo, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6B, FI-80101 Joensuu, Finland ORCID ID: – E-mail: erkki.verkasalo@luke.fi
article id 10052, category Research article
(2019). Effect of pruning season and tool on knot occlusion and stem discolouration in Betula pendula – situation five years after pruning. Silva Fennica vol. 53 no. 1 article id 10052. https://doi.org/10.14214/sf.10052
Highlights: The occlusion was the fastest in the case of small living branches of fast growing trees pruned in springtime; Occlusion was quicker after saw pruning than after secateurs pruning, due to shorter knot stubs; Branches that were pruned in living state occluded faster than the ones pruned as dead; Dead branches hit down with a stick occluded slowly.
This paper investigates and models the effects of pruning season and tool on wound occlusion with varying tree and branch characteristics of silver birch (Betula pendula Roth) stems at the pruning height of 0−4 metres. Dates of eight secateurs prunings, three saw prunings and two sticks prunings as well as unpruned control were tested in permanent plots on four sites. Knot occlusion and discolouration in stemwood were measured from about 1600 studied knots of 112 sample trees felled five to six years after pruning in 2010. Knot occlusion rate was modelled according to pruning tool, date, tree growth, and branch characteristics. The occlusion was the fastest in trees pruned in spring or early summer, and the slowest in trees pruned in autumn. Stubs of living branches occluded faster than the dead ones with the same diameter. Saw pruning resulted in clearly better occlusion rates than secateurs pruning, caused by the shorter knot stubs after saw pruning. Hitting dead branches away with a stick resulted in the worst occlusion status. The colour defects spread more often upward from the knot than downward. Discolouration in stemwood was detected more frequently near to the pruned branches than the unpruned ones, and more widely near to the stubs of dead branches than the living ones. Most saw and secateurs pruned branches were completely occluded during the experiment, so these prunings were suitable for all branches under 20 mm in diameter, and for living branches even up to 30 mm in fast-growing trees.
- Niemistö, Natural Resources Institute Finland (Luke), Natural resources, Kampusranta 9 C, FI-60320 Seinäjoki, Finland ORCID ID: – E-mail: pentti.niemisto@luke.fi
- Kilpeläinen, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6 B, FI-80100 Joensuu, Finland ORCID ID: – E-mail: harri.kilpelainen@luke.fi
- Heräjärvi, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6 B, FI-80100 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@luke.fi
article id 117, category Research article
(2011). Saw log recovery and stem quality of birch from thinnings in southern Finland. Silva Fennica vol. 45 no. 2 article id 117. https://doi.org/10.14214/sf.117
Keywords: Betula pendula; Betula pubescens; European white birch; silver birch; thinning; saw logs; stem quality; stem defects; bucking; recovery
The objective of this study was to examine the timber quality of silver birch (Betula pendula Roth) and European white birch (Betula pubescens Ehrh.) trees in the first and second thinnings in southern parts of Finland, from the viewpoint of sawing of small-diameter, short logs, in particular. The average stem volume of birch was 0.140 m3 in the first thinning stands and 0.206 m3 in the second thinning stands. In planted stands, the trees were larger in the first thinnings but slightly smaller in the second thinnings, compared with naturally regenerated pure birch stands or mixed stands of Norway spruce and birch species. Almost 60% of the harvested and 35% of the remaining stems that could provide saw logs were graded as pulpwood for timber quality due to the occurrence of stem defects. The most common stem defects were multiple crooks and middle crooks. Only minor between-stratum differences were detected in the numbers of defects. Depending on the bucking option, the total percentage of saw and plywood logs from the total birch recovery in the thinning of the sample stands varied between 11.7 and 18.2. The recovery of saw logs was clearly higher in the second thinnings, 12–19%, than in the first thinnings, 8–14%. Of the stand types, saw log recovery was the highest in planted birch stands, 12–19%, but lower in naturally regenerated pure birch stands and mixed stands of Norway spruce and birch. The highest share of saw logs was in the second thinning of planted stands, 17–25%. This study shows that the harvesting recoveries of end-use based timber assortments can be estimated in different kinds of thinning birch stands. Based on tree and log dimensions and stem squality, silver birch firstly from plantations and secondly from mixed stands should be the most interesting source of raw material for the saw milling, furniture and interior product sectors.
- Kilpeläinen, Finnish Forest Research Institute, Eastern Finland Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland ORCID ID: – E-mail: –
- Lindblad, Finnish Forest Research Institute, Eastern Finland Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland ORCID ID: – E-mail: –
- Heräjärvi, Finnish Forest Research Institute, Eastern Finland Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@metla.fi
- Verkasalo, Finnish Forest Research Institute, Eastern Finland Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland ORCID ID: – E-mail: –
article id 198, category Research article
(2009). Effect of drying technology on aspen wood properties. Silva Fennica vol. 43 no. 3 article id 198. https://doi.org/10.14214/sf.198
This article reports the impacts of three different drying treatments on selected physical and mechanical properties of European (Populus tremula L.) and hybrid (P. tremula x tremuloides) aspen wood. The material originates from 5 European aspen stands and 7 hybrid aspen stands in southern and central Finland. After processing the logs at a saw mill, sawn timber samples were dried using 1) conventional warm air drying, 2) press drying, or 3) heat treatment into Thermo-S grade by the Finnish Thermowood® method. Finally, small clearwood specimens were manufactured from different within-stem positions for the measurements of physical and mechanical properties. Both press dried and heat treated specimens absorbed water at significantly slower pace than the conventionally dried specimens. In normal climate, the conventionally dried, press dried and heat treated specimens conditioned at equilibrium moisture contents of 12.2, 8.7, and 8.9 per cent, respectively. It appears that the butt logs between 2–6 metres contain the lightest and, thus, weakest wood in aspen stems. Radial compression strength was at its highest in heat treated specimens, whereas conventionally and press dried specimens did not differ from each other. Press dried specimens had the highest longitudinal compression strength, also heat treated specimens showed higher values than the conventionally dried ones. Radial Brinell hardness of press dried specimens was higher than that of conventionally dried or heat treated specimens. Both modulus of elasticity and modulus of rupture were at their highest in press dried specimens. Irrespective of the drying treatment, the tangential shear strength of European aspen specimens was approximately 5% higher than that of hybrid aspen. Heat treated specimens indicated significantly lower tangential shear strength values than the conventionally dried ones. In case of both aspen species, the longitudinal tensile strengths of heat treated specimens were significantly lower than those of conventionally and press dried specimens. Heat treated specimens had the highest variability among the results. The inherent flaws in aspen wood material, e.g., wetwood and density
- Heräjärvi, Metla, Joensuu Research Unit, Box 68, FI-80101 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@metla.fi
article id 258, category Research article
(2008). Influence of saw and secateur pruning on stem discolouration, wound cicatrisation and diameter growth of Betula pendula. Silva Fennica vol. 42 no. 2 article id 258. https://doi.org/10.14214/sf.258
The aim of this case study was to compare the impacts of saw and secateur pruning on silver birch (Betula pendula Roth). Data were collected from two saw pruned stands in 2005, and one secateur pruned stand in 2003. All the stands were located in southern Finland. The sample stems were felled, and their butt logs were sawn into flitches, whose knot features and colour defects were measured. In addition, discs were sawn from each stem in order to study the annual ring widths. In this material, pruning with secateurs appeared to cause less colour defects than pruning with a saw. Irrespective of the pruning method used, the colour defects in the stem wood were at their largest in cases where the basal knob or the stem bark appeared to be damaged by pruning. Colour defects spread mainly towards the pith, only in a few cases towards the stem surface. The cicatrisation time of the knots as well as the length of the bark stick remaining inside the stem did not show significant differences between the two pruning methods. Pruning of the lowest living branches appears to have no effect on the diameter growth of silver birch trees.
- Schatz, Peltotievantie 27, FI-99440 Leppäjärvi, Finland ORCID ID: – E-mail: –
- Heräjärvi, Finnish Forest Research Institute, Joensuu Research Unit, P.O. Box 111, FI-80101 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@metla.fi
- Kannisto, Finnish Forest Research Institute, Parkano Research Unit, Kaironiementie 54, FI-39700 Parkano, Finland ORCID ID: – E-mail: –
- Rantatalo, Peltotievantie 27, FI-99440 Leppäjärvi, Finland ORCID ID: – E-mail: –
article id 581, category Research article
(2001). Technical properties of mature birch (Betula pendula and B. pubescens) for saw milling in Finland. Silva Fennica vol. 35 no. 4 article id 581. https://doi.org/10.14214/sf.581
The purpose of this study was to investigate the variation in selected technical properties of mature (age > 60 years) birch stems in southern and central Finland. Technical properties were defined as the natural external characteristics that cause differences in the usability of a certain section of stem in the mechanical wood industry, saw milling in particular. On mineral soils, birch stems in mixed stands were slightly larger than those in pure birch stands. On peatlands, however, birch stems in pure stands were larger than those in mixed stands. The average stem form of silver birch was straighter than that of white birch. Small-sized log sections of white birch, as well as those of codominant silver birch, typically contain many dead knots. On mineral soils, coniferous admixture had a positive effect on self-pruning of white birch. Self-pruning of silver birch was as good in pure birch stands as in mixed stands of spruce and birch. Occurrence of decay did not differ significantly between the two birch species. Not only silver birch, due to the growth and yield of the stand, but also vigorous and good-quality white birch, because of the possibility to provide high-quality logs, can be maintained profitably as an admixture in coniferous forests until final cutting.
- Heräjärvi, The Finnish Forest Research Institute, Joensuu Research Centre, P.O. Box 68, FIN-80101 Joensuu, Finland ORCID ID: – E-mail: henrik.herajarvi@metla.fi
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