SEEFOR 17(1): 26002
Article ID: 26002
DOI: https://doi.org/10.15177/seefor.26-002
ORIGINAL SCIENTIFIC PAPER
Analysis of Wood Defects in Norway spruce (Picea abies (L.) Karsten) from Mixed Uneven-Aged Forest Stand
Jelena Knežević1,*, Jusuf Musić1, Velid Halilović1, Aldin Hodžić2, Ehlimana Pamić1, Amina Karišik1
Addresses:
(1) University of Sarajevo, Faculty of Forestry, Chair for Forest Utilization, Planning and Building in Forestry and Horticulture, Zagrebačka 20, BA-71000 Sarajevo, Bosnia and Herzegovina;
(2) Igmanska 11, BA-71320 Vogošća, Bosnia and Herzegovina
Citation: Knežević J, Musić J, Halilović V, Hodžić A, Pamić E, Karišik A, 2026. Analysis of Wood Defects in Norway Spruce (Picea abies (L.) Karsten) from Mixed Uneven-Aged Forest Stand.. South-east Eur for 17(1): 26002. https://doi.org/10.15177/seefor.26-002.
Received: 13 Oct 2025; Revised: 24 Dec 2025; Accepted: 26 Dec 2025; Published online: 24 Feb 2026
Cited by: Google Scholar
Abstract
Norway spruce (Picea abies (L.) Karsten) is one of the most economically important conifer species in Europe. Efficient utilisation and processing of its wood require detailed knowledge of its technical properties, as well as the most common wood defects that substantially affect both properties and utilisation. Given the crucial role of wood defects in the roundwood classification system, the primary objective of this study was to identify defects in Norway spruce and to analyse the influence of forest assortment characteristics (diameter and position along the stem) and tree attributes (diameter at breast height and position within the stand) on the size of wood defects. The research was conducted in Bosnia and Herzegovina, within a forest compartment of an uneven-aged, mixed beech and silver fir stand with spruce. Trees were felled and processed into assortments using a chainsaw, predominantly applying the cut-to-length method. After measuring the assortment dimensions, the occurrence of defects was assessed, and their sizes were determined. The analysis showed that, following knots, the most common wood defect was rot, followed by pith eccentricity, compression wood, scars, mechanical damage, and resin pockets. Statistically significant differences were found in the size of knots, ellipticity, and taper among different diameter classes of assortments (p<0.05), as well as assortment positions along the stem (p=0.0000). Also, a statistically significant difference was observed in the size of the knots and ellipticity in relation to both diameter at the breast height and tree position within the stand (p<0.05). Overall, the findings align with previous studies, confirming the higher quality of the lower stem section, as reflected in smaller defect sizes critical for roundwood quality classification, such as knots, rot, ellipticity, and taper.
Keywords: quality classification; roundwood; wood defect; knots; rot
INTRODUCTION
Norway spruce (Picea abies (L.) Karsten) is one of the most economically significant conifer species in Europe. Its high productivity and wood quality across diverse site conditions distinguish it from other species (Skrøppa 2003). Owing to its favourable mechanical properties and low density, Norway spruce wood is widely used in construction and the furniture industry (Šoškić et al. 2008). The proper use and processing of wood require knowledge of its technical properties, as well as of the most common wood defects that significantly affect its performance and utilisation. The quality structure of forest wood assortments depends on numerous factors, primarily the dimensions of the assortment and the size of external defects (knots, etc.), and to a lesser extent internal defects (rot, etc.), as well as damage incurred during tree felling and processing (Krajnc et al. 2023). The external appearance of a tree and its properties, such as stem form, branching, bark features, anatomical structure, and wood colour, are determined by a range of characteristics that develop during its normal life cycle. Environmental factors, including temperature fluctuations, precipitation, snow, wind, and light, also affect tree growth. Biological influences, such as attacks by fungi, insects, animals, parasitic plants, and human activities, likewise play a significant role (Richter 2015). Wood defects thus result from the combined effects of biotic, abiotic, and anthropogenic factors, and can occur on the stem, branches, and roots.
A particular characteristic of a tree resulting from growth under varying conditions may sometimes be regarded as a defect, and at other times not. When viewed from the perspective of tree growth, only those features that shorten the expected lifespan of the tree, such as rot or stem breakage, are considered defects. Irregular stem shape and knots, for example, are not regarded as defects from a biological standpoint. However, from the perspective of wood utilisation, defects are characteristics that make the use of wood for a specific purpose difficult or impossible (Richter 2015). In forestry practice of Bosnia and Herzegovina, wood defects are commonly defined according to Gurda and Musić (2015) as deviations from the normal structure, form, colour, or properties of wood, particularly those that reduce its usability. The quality classification of wood, according to the applicable standards in Bosnia and Herzegovina (Yugoslav standards), is based on the presence, size, and frequency of wood defects, as well as the dimensions of the wood assortments (diameter and length).
Knots, rot, scars, curvature, compression wood, spiral grain, hazel wood, sunburn bark, resin pockets, burls, ring shakes, mechanical damage and damage caused by insects are cited as the most common wood defects in Norway spruce (Ugrenović 1950, Karahasanović 1992, Barszcz and Michalec 2007). Previous studies of Norway spruce identify knots and rot as the wood defects with the greatest negative impact on wood quality (Barszcz et al. 2010a, 2010b, Michalec et al. 2013, Kadunc 2013, Vlad et al. 2018, Noordermeer et al. 2023, Lara et al. 2024).
Spruce wood contains resin pockets, which can reduce its usability and commercial value. Resin pockets directly affect the aesthetic quality of wood products. The leakage of resin produces a sticky layer on contact with objects or people, which poses a greater disadvantage for carpentry applications than for construction wood. These negative effects have led to the number and size of resin pockets being regulated in national standards for wood classification (Gjerdrum and Bernabei 2006). Gryc and Horáček (2007) found that the density of Norway spruce wood is higher when compression wood is present. In cases where compression wood accounts for 80% of the stem, the wood density is 1.5 times greater compared to wood without this defect. Due to the higher density, working with compression wood results in increased energy consumption. Additionally, products containing compression wood exhibit a different colour, which may be considered an undesirable trait unless otherwise specified. Gryc and Vavrčík (2009) reported that the compressive strength parallel to the grain of Norway spruce compression wood is slightly higher than that of wood without the defect, reaching a value of 50 MPa.
The effects of bark beetle infestation on the tensile and compressive strength of Norway spruce wood were studied by Löwe et al. (2022). They reported that the longer trees remain in the stand after infestation, the greater is the reduction in these strength properties. In trees infected three years prior to analysis, tensile strength decreased by 14% compared to healthy trees (from 93.185 MPa to 80.709 MPa), while compressive strength declined by 25.6% (from 46.144 MPa to 34.318 MPa).
Lojo et al. (2021) found that the proportion of Norway spruce logs increases significantly with tree diameter. They also highlighted the influence of tree height on assortment volume, noting that taller trees produce a greater volume of high-quality assortments within the same diameter class.
Considering the previously emphasized importance of wood defects in the classification system of roundwood, the primary aim of this study was to identify wood defects in Norway spruce and to analyse the influence of forest wood assortment characteristics (diameter and position along the stem), as well as tree attributes (diameter at breast height and position within the stand), on the size of specific wood defects.
MATERIALS AND METHODS
The research was conducted in Bosnia and Herzegovina, in a forest compartment within an uneven-aged, mixed beech and silver fir forest with spruce, growing on shallow cambisol, leptosol and their complexes on limestone and dolomite, and phaeozems on saccharoid limestone and dolomites. The study area is located at 43°45'16'' N and 18°14'47'' E. Average elevation in forest compartment is 1,310 m, with terrain slope ranging from 10° to 25°. In 2023, trees were selected for felling according to the group selection system principles, with a total of 2,766 m3 of merchantable wood (not smaller than 7 cm over-bark) marked. Field research focused on wood defect analysis was carried out in November 2024. A total of 30 Norway spruce trees were included in the study. To minimise sampling bias, trees were analysed consecutively along the felling lines, regardless of their external characteristics. Before tree felling, the diameter at breast height (DBH) and position within the stand were recorded for each analysed tree. DBH (measured at 1.3 m above ground level) was determined using a caliper. Tree position within the stand was classified according to Kraft’s classification (1884), assigning each tree to one of five categories: predominant, dominant, co-dominant, suppressed, or overtopped.
The trees were felled and processed into forest wood assortments using a chainsaw. The cut-to-length processing method was predominantly applied, while the half-tree length method was used to a lesser extent. Length and diameter of all processed assortments were measured immediately after felling. Length was measured at the shortest point of each assortment using a measuring tape. Diameters were measured with a caliper at designated points crosswise (maximum and minimum), with values rounded down to the nearest centimeter. The reduction from over-bark to under-bark diameter was performed by subtracting double bark thickness in the amount of 1 cm for forest wood assortments with diameters up to 35 cm at the middle of length, and 2 cm for those with diameters exceeding 35 cm, in accordance with the internal regulations of the enterprise managing the forests in the study area. Diameters were recorded at three positions along each wood assortment: the thicker end, the middle of the length, and the thinner end. For the first assortment taken from the base of the tree, two crosswise diameters were measured at the root collar end, located at a maximum distance of 1 m from the thicker end instead of measuring diameter at the thicker end. The volume of forest wood assortments was determined using Huber’s formula (Equation 1) cited in Banković and Pantić (2006).
V = g ½ · L (1)
where V is volume of wood assortment (m3), g ½ is basal area at the middle of length (m2), and L is length of wood assortment (m).
After measuring the assortment dimensions, the presence of wood defects was analysed and their sizes were determined. Defects were measured according to the national Yugoslav standard from 1969 (JUS D.A0.101 - Wood Defects: Terminology, Definitions, and Measurement). The formulas used to calculate the size of individual defects are presented in Table 1.
Table 1.Formulas for calculating wood defect sizes.
For some defects (split tree stem, compression wood, resin pockets, ingrown bark, and insect damage), only their presence or absence was determined.
Knots were classified according to the following criteria: mutual position (individual knots; knots in a whorl), degree of their tightness with the surrounding wood (tight or intergrown; partially intergrown; encased or loose knots), health status (sound; partially rotten; rotten), and size (pin knots <6 mm; small knots 7–20 mm; medium knots 21–40 mm; large knots >41 mm). A similar classification of knots can be found in Barszcz et al. (2010a, 2010b). For knot size classification, the smallest diameter of an individual knot was recorded, whereas for knots in a whorl, the smallest diameter of the largest knot was measured.
Statistical data processing was performed using the Statgraphics Centurion XVII software package. After testing for data normality (Shapiro-Wilk W-test) and homogeneity of variance (Levene’s test), the ANOVA or Kruskal-Wallis non-parametric test was applied to analyse the influence of forest wood assortment and tree characteristics on the size of wood defects. χ2 test was used to determine compression wood occurrence depending on wood assortment and tree characteristics.
RESULTS AND DISCUSSION
The research included 30 Norway spruce trees with an average DBH of 71.17 cm (±15.39 cm), ranging from 22 to 94 cm. The total gross volume of all analysed trees was 141.289 m3, corresponding to an average of 4.710 m3 per tree. From these trees, 133 wood assortments were processed (Table 2). Sawlogs accounted for 76.58% of the total volume of processed forest assortments, followed by pulpwood with 21.18% and round pit timber with 2.24%.
Table 2. Features of processed wood assortments.
Analysis of the processed forest assortments revealed that after knots, the most prevalent defect was rot, observed in 56.67% of the analysed trees. Pith eccentricity and compression wood were each recorded in 50% of the trees. Scars were observed in 26.67% of trees, whereas damage from physical and mechanical factors and resin pockets were present in 20% of cases each. Other recorded wood defects (double heart, curvature, split tree stem, ingrown bark, and insect damage) were present in 10% or fewer of the analysed trees (Figure 1). The most frequent wood defects are presented in Figure 2.
Some of the commonly reported wood defects in Norway spruce trees (Ugrenović 1950, Karahasanović 1992, Barszcz and Michalec 2007, Sandak et al. 2020) were also observed in this study, including compression wood, resin pockets, curvature, rot, scars, mechanical damage, and insect damage. Other defects frequently cited in the literature, such as spiral grain, hazel wood, sunburn bark, burls, and ring shakes, were not observed in the analysed trees.
Knots were predominantly in whorls (80.76%), tight (87.09%) and sound (92.87%) (Figure 3). Barszcz et al. (2010a) also found that sound-tight knots prevailed (60%) in mature 150-year-old Norway spruce stands situated at an altitude of 1,450-1,740 m above sea level in northern Italy. Medium-sized knots (21–40 mm) and large knots (>41 mm) were the most frequently found. Small knots (7–20 mm) comprising 15.28% of the total. Based on measurements of 1,263 individual knots and knots in a whorl, it was determined that its size ranged from 10 mm to 75 mm, with an average of 33.81 mm. The average knot diameter was higher than 20.3 mm reported by Barszcz et al. (2010a) in 150-year-old Norway stands situated at an altitude of 1,450–1,740 m above sea level in northern Italy.
Rot was measured at both the thicker and thinner ends of the logs. The average extent of rot at the thicker end of the assortments was 51.65%, ranging from 10.19% to 100%. At the thinner end, the average extent of rot was slightly higher, 67.63%, ranging from 10.19% to 94.34%.
The average scar size was 561.55 cm², with the majority of scars (81.82%) observed on the first and second assortments, moving upward from the base of the tree toward the crown. The average size of damage caused by physical and mechanical impacts was 598.11 cm². The highest incidence of damage caused by physical and mechanical impacts was also recorded in the lower part of the stem, specifically on the first assortment (44.44%) and second assortment (44.44%). These findings support the well-established fact that the lower stem section is the most susceptible to injuries during timber extraction by cable skidders, which are commonly used in forest harvesting in Bosnia and Herzegovina. Kadunc (2013) notes that mechanical damage is a significant factor influencing the occurrence of wood rot in Norway spruce. Also, Michalec et al. (2013) stated that Norway spruce is highly susceptible to mechanical stem damage, which can rapidly lead to rot. Several researchers have investigated fungi affecting Norway spruce trees. Lara et al. (2024) stated that the presence of fungi from genera Heterobasidion and Armillaria results in financial losses and a reduction in the usable wood volume. Also, Noordermeer et al. (2023) report that butt end rot is the most significant defect in Norway spruce, causing substantial financial losses. In a study of 140,000 m³ of felled spruce wood in Norway, 16% of trees showed rot, with a higher incidence in larger-diameter trees. When root rot is present, the volume of sawlogs is reduced by 48%. The same authors also reported that the presence of wood rot reduces timber revenue by 7%, corresponding to approximately 18.5 million euros in Norway. According to Kadunc (2013) wood rot in Norway spruce can reduce timber value by up to 19 €·m-³, with the most significant losses observed in the 50–70 cm diameter class. Therefore, careful consideration is required when conducting harvesting operations in spruce stands. In this study, injuries (damage caused by physical and mechanical impacts and/or scars) were observed in 41.18% of trees in which rot was recorded.
Compression wood was found in 23.31% of wood assortments. The χ² test was used to analyse the occurrence of compression wood in relation to the characteristics of processed wood assortments and the tree (Table A1, Table A2, Table A3, and Table A4). A statistically significant difference was found in the proportions of assortments with and without compression wood across different stem sections (p=0.0206). For the other analysed factors (assortment diameter, DBH, and position within the stand), no statistically significant effects were observed (p>0.05). This wood defect was most frequently observed in the first assortment (45.16%), while in the upper parts of the stem, in the fourth and fifth assortments, it was recorded in only 19.63% of cases. No defects were observed in the sixth assortment. The distribution of compression wood along the stem is consistent with the findings of Warensjö (2003), who reported that this wood defect is typically most pronounced near the ground and decreases toward the upper parts of the stem.
The pith eccentricity varied from 6.77% to 24.47% at the thicker end, and from 6.77% to 24.14% at the thinner end. The lower number of defects recorded at the thinner end (16) compared to the thicker end (29) supports the observation that these defects tend to disappear at a certain height of the tree.
Resin pockets were found in 5.26% of the wood assortments. The defect was recorded at tree heights ranging from 6.54 m to 25.11 m, with an average height of 14.99 m. These results are consistent with the findings of Gjerdrum and Bernabei (2006), Temnerud (1997), and Seifert et al. (2010), which report an increased occurrence of resin pockets with increasing height in Norway spruce trees.
The ellipticity at different positions (thicker end, root-collar end, mid-length, and thinner end), as well as the taper for each wood assortment, were determined. Ellipticity ranged from 0% to 9.09%. The applicable JUS standard defines a section as regular if its ellipticity is less than 10%. Analysis of ellipticity measured along different lengths of the wood assortments showed that this defect did not exceed the threshold value in any case. Taper ranged from 0.96% to 19.41%, with a mean of 5.01%.
The relationship between the wood defect size and the diameter of processed forest assortments, as well as their position along the stem, was analysed. The analysis focused on the most frequent wood defects identified in this study (knots, rot, and pith eccentricity) and on ellipticity and taper, which were determined for each wood assortment. The diameter at mid-length of the forest wood assortment was considered in the analysis. The position along the stem was defined by the assortment's ordinal number (1–6), with assortment 1 corresponding to the lowest position on the stem, closest to the ground.
A statistically significant difference (Table 3 and Table 4) was found in the size of knots, ellipticity and taper for different diameter classes of processed forest wood assortments (p< 0.05), as well as for different assortment positions along the stem (p=0.0000). Larger knots were observed in thinner assortments originating from the upper part of the stem. The smallest knot sizes were recorded within assortments with diameters from 81 cm to 90 cm, as well as the first assortment in the stem, near the ground. Similar results regarding the size of the knots along the stem were obtained by Barszcz et al. (2010a). Ellipticity decreases with increasing assortment diameter. On the other hand, with respect to position within the stem, the relationship is inverse: ellipticity increases from the root collar toward the crown. Exceptions are 71–80 cm the 81–90 cm diameter classes, as these assortments belong to the first stem section of old trees, where the root collar deformation caused higher ellipticity. Taper decreases from thinner to thicker assortments and increases from the root collar toward the crown. The deviation from trend is expressed in the 81-90 cm diameter class, and the first assortment from the stem, similar to ellipticity.
Table 3. Analysis of the influence of assortment diameter on the wood defect size.
Table 4. Analysis of the influence of assortment position on the wood defect size.
The relationship between the size of wood defects and tree characteristics (DBH and position within the stand) was also analysed (Table 5 and Table 6). A statistically significant difference was observed in the size of the knots and ellipticity in relation to both DBH and tree position within the stand (p<0.05). The largest knots were found in trees with DBH >81 cm and in "predominant trees". The largest size of ellipticity was observed in trees with DBH from 21 cm to 30 cm, and in "co-dominant trees". The result of the previous study (Noordermeer et al. 2023) showed that root collar rot in Norway spruce is more common in trees with larger DBH. Also, Chomicz (2013) emphasised the relationship between tree age and the occurrence of butt end rot in Norway spruce under comparable stand and site conditions, reporting that the probability of rot increases with tree age. However, in this case, no statistically significant effect of DBH on rot occurrence was observed.
Table 5.Analysis of the influence of DBH on the wood defect size.
Table 6. Analysis of the influence of tree position within stand on the wood defect size.
CONCLUSIONS
The research results on the identified wood defects are consistent with previous findings of higher quality in the lower stem, as reflected in smaller defect sizes relevant to roundwood quality classification, such as knots, rot, ellipticity, and taper. Exceptions are pith eccentricity and compression wood, which are more frequent in the lower part of the stem. Additionally, the highest number of scars and damage from physical and mechanical factors was observed in the lower part of the stem, particularly in the first and second assortments from the ground. Given that scars and/or damage from physical and mechanical factors, most often caused by skidders during the wood extraction phase, were confirmed in a large number of trees affected by rot, the necessity of implementing protective measures to preserve the residual trees in the stand during forest harvesting is emphasised. The use of harvesters in uneven-aged mixed stands in Bosnia and Herzegovina requires mathematical models of individual tree species’ morphology, as well as the occurrence and size of the most common wood defects, to enable accurate automatic bucking. Consequently, continued research is needed to expand the database of wood defects and to develop reliable mathematical models. Also, future research is planned to focus on assessing the importance of the analysed factors through their influence on the value structure.
Author Contributions
JK and AH conceived and designed the research and carried out the field measurements; JK, AH, EP and AK processed the data and performed the statistical analysis; JK and JM supervised the research and helped to draft the manuscript; JK, JM and VH wrote the manuscript.
Funding
This research received no external funding.
Conflicts of Interest
The authors declare no conflict of interest.
Apendix
Table A1. Analysis of the dependence of compression wood occurrence on diameter of wood assortment.
Table A3. Analysis of the dependence of compression wood occurrence on DBH.
REFERENCES
Banković S, Pantić D, 2006. Dendrometrija [Dendrometry]. University of Belgrade, Faculty of Forestry, Belgrade, Serbia, 556 p. [in Serbian].
Barszcz A, Michalec K, 2007. Spruce timber quality in trees with different thickness from the Beskidy MTS. Acta Sci Pol 6(3): 5-15.
Barszcz A, Sandak A, Sandak J, 2010a. Size and localisation of knots in timber from mountain spruce stands in the Dolomites. Folia For Pol A 52(1): 13-19.
Barszcz A, Sandak A, Sandak J, 2010b. Knottiness of spruce stems from the Dolomites as the basis for distinguishing quality zones in roundwood. Folia For Pol A 52(2): 89-97.
Chomicz E, 2013. Incidence of butt rot in Norway spruce seed stands in Poland’s mountain regions assessed with sonic tomography. Folia For Pol A. 55 (4): 174-180.
Gjerdrum P, Bernabei M, 2006. Three-dimensional model for size and location of resin pockets in stems of Norway spruce. Holz Roh Werkst 65: 201-208. https://doi.org/10.1007/s00107-006-0158-0.
Gryc V, Horáček P, 2007. Variability in density of spruce (Picea abies [L.] Karst.) wood with the presence of reaction wood. J For Sci 53(3): 129-137.
Gryc V, Vavrčík H, 2009. Variability of spruce (Picea abies [L.] Karst.) compression strength with present reaction wood. J. For Sci 55(9): 415-422.
Gurda S, Musić J, 2015. Anatomija i greške drveta [Anatomy and Defects of Wood]. University of Sarajevo, Faculty of Forestry, Sarajevo, Bosnia and Herzegovina, 239 p. [in Bosnian].
Kadunc A, 2013. The Incidence of Rot in Norway Spruce and its Influence on the Value of Trees in Slovenia. Croat J For Eng 34(1): 137-149.
Karahasanović A, 1992. Nauka o drvetu [Wood Science]. Publishing company Svjetlost, Institute for Textbooks and Teaching Aid, Sarajevo, Bosnia and Herzegovina, 426 p. [in Bosnian].
Kraft G, 1884. Beiträge zur Lehre von Durchforstungen, Schlagstellungen und Lichtungshieben [About thinnings, cutting systems and shelterwood cuttings]. Klindworth Verlag, Hannover, Germany, 147 p. [in German].
Krajnc L, Arnič D, Prislan P, 2023. Analiza kakovostne strukture okroglega lesa listavcev [The distribution of different log grades by volume in three hardwood species]. Les/Wood 72(1): 49-58. https://doi.org/10.26614/les-wood.2023.v72n01a05. [in Slovenian].
Lara W, Astrup R, Hietala AM, Maleki K, Belbo H, Antón-Fernández C, 2024. Mapping pathogenic fungi in decayed Norway spruce stands: Insights from harvester positional data. J Appl Ecol 00: 1-12. https://doi.org/10.1111/1365-2664.14800.
Lojo A, Musić J, Balić B, Avdagić A. 2021. Wood assortment tables of Norway spruce (Picea abies Karst.) for Canton 10 of Federation B&H. Works of the Faculty of Forestry University of Sarajevo 50(2): 3-19. https://doi.org/10.54652/RSF.2020.V50.I2.344.
Löwe R, Sedlecký M, Sikora A, Prokůpková A, Modlinger R, Novotný K, Turčáni M, 2022. How Bark Beetle Attack Changes the Tensile and Compressive Strength of Spruce Wood (Picea abies (L.) H. Karst.). Forests 13(1): 87. https://doi.org/10.3390/f13010087.
Michalec K, Barszcz A, Wasik R, 2013. Jakość surowca świerkowego pochodzącego z drzewostanów naturalnych (rezerwatowych) i drzewostanów pełniących funkcje gospodarcze [The quality of spruce timber from natural stands (forest reserves) and managed stands]. Drewno 56(189): 25-37. https://doi.org/10.12841/wood.1644-3985.029.02. [in Polish].
Noordermeer L, Korpunen H, Berg S, Gobakken T, Astrup R, 2023. Economic losses caused by butt rot in Norway spruce trees in Norway. Scand J For Res 38(7-8): 1-9. https://doi.org/10.1080/02827581.2023.2273252.
Richter C, 2015. Wood Characteristics. Description, Causes, Prevention, Impact on Use and Technological Adaptation. Springer, Cham, Switzerland, 222 p. https://doi.org/10.1007/978-3-319-07422-1.
Sandak J, Sandak A, Zitek A, Hintestoisser B, Picchi G, 2020. Development of Low-Cost Portable Spectrometers for Detection of Wood Defects. Sensors 20(2): 545. https://doi.org/10.3390/s20020545.
Seifert T, Breibeckb J, Seifert S, Biberb P, 2010. Resin pocket occurrence in Norway spruce depending on tree and climate variables. For Ecol Manag 260(3): 302-312. https://doi.org/10.1016/j.foreco.2010.03.024.
Skrøppa T, 2003. EUFORGEN Technical Guidelines for genetic conservation and use for Norway spruce (Picea abies). International Plant Genetic Resources Institute, Rome, Italy, 6 p.
Šoškić B, Govedar Z, Todorović N, Petrović D, 2008. Čvrstoća na pritisak i tvrdoća drveta smrče (Picea abies Karst.) iz kultura [Compressive strength and hardness of spruce (Picea abies Karst.) wood from plantations]. Šumarstvo 3: 119- 135. [in Serbian].
Temnerud E, 1997. Formation and Prediction of Resin Pockets in Picea abies (L.) Karst. PhD Thesis, Swedish University of Agricultural Sciences, Department of Forest Products, Uppsala, Sweden, 56 p.
Ugrenović A, 1950. Tehnologija drveta [Wood Technology]. Croatian Publishing House, Zagreb, Croatia, 502 p. [in Croatian].
Vlad R, Zhiyanski M, Dincă L, Sidor CG, Constandache C, Pei G, Ispravnic A, Blaga T, 2018. Assessment of the density of wood with stem decay of Norway spruce trees using drill resistance. C R. Acad Bulg Sci 71(11): 1502-1510. https://doi.org/10.7546/CRABS.2018.11.09.
Warensjö M, 2003. Compression wood in Scots pine and Norway spruce - Distribution in relation to external geometry and the impact on dimensional stability in sawn wood. PhD Thesis, Swedish University of Agricultural Sciences, Department of Forest Products and Markets, Umeå, Sweden, 36 p.
Yugoslav Institute for Standardization, 1969. Greške drveta: Terminologija, definicije i mjerenje (JUS D.A0.101) [Wood Defects: Terminology, Definitions, and Measurement (JUS D.A0.101)]. [in Yugoslavian].
© 2026 by the Croatian Forest Research Institute. This is an Open Access paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0).