Mechanical properties of grand fir wood grown in the Czech Republic in vertical and horizontal positions

Abstract

Strength properties were evaluated for Grand fir wood (Abies grandis /Douglas/ Lindl.), a North American species that is considered to be a promising species for the Central European forestry industry. The bending, compression, and impact strengths of wood from Grand fir trees grown in the Czech Republic area were tested, including their variability within a stem and correlation to wood density. The average values of the compression strength reached 39.577 MPa; the bending strength was 78.119 MPa, the impact strength was 4.186 J/cm2, and the density was 410.267 kg/m3. The greatest dependence of the strength characteristics on the evaluated density was shown in the case of bending at the vertical bottom position (r = 0.95). Compression strength values were observed to highly correlate with the density at vertical positions (bottom and middle) in the first site (r = 0.98). The values of the correlations between density and impact strength were observed to be moderate or poor in the vertical position, where a good value was shown in the middle position (r = 0.87). The results of the study suggest that Grand fir is a satisfactory substitute for indigenous species of fir in the Czech Republic; with respect to bending strength and toughness, it can replace the most important commercial conifer, spruce.

Full Article

Mechanical Properties of Grand Fir Wood Grown in the Czech Republic in Vertical and Horizontal Positions

Aleš Zeidler,^a Mohamed Z. M. Salem,^b,c,* and Vlastimil Borůvka ^a

Strength properties were evaluated for Grand fir wood (Abies grandis /Douglas/ Lindl.), a North American species that is considered to be a promising species for the Central European forestry industry. The bending, compression, and impact strengths of wood from Grand fir trees grown in the Czech Republic area were tested, including their variability within a stem and correlation to wood density. The average values of the compression strength reached 39.577 MPa; the bending strength was 78.119 MPa, the impact strength was 4.186 J/cm², and the density was 410.267 kg/m³. The greatest dependence of the strength characteristics on the evaluated density was shown in the case of bending at the vertical bottom position (r = 0.95). Compression strength values were observed to highly correlate with the density at vertical positions (bottom and middle) in the first site (r = 0.98). The values of the correlations between density and impact strength were observed to be moderate or poor in the vertical position, where a good value was shown in the middle position (r = 0.87). The results of the study suggest that Grand fir is a satisfactory substitute for indigenous species of fir in the Czech Republic; with respect to bending strength and toughness, it can replace the most important commercial conifer, spruce.

Keywords: Grand fir; Introduced species; Wood properties; Strength; Density; Variability

Contact information: a: Department of Wood Processing, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic; b: Forestry and Wood Technology Department, Faculty of Agriculture (EL–Shatby), Alexandria University, Egypt; c: Department of Wood Products and Wood Constructions, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic; *Corresponding author: zidan_forest@yahoo.com

INTRODUCTION

At the end of the 20^th century, the Czech forestry faced a radical change in species composition, i.e., substitution of the silver fir (Abies alba Mill.), a significant original domestic softwood, that decreased from an original representation of 19.8% to just 1.0% in 2012 (Ministry of Agriculture 2012). Historically, silver fir was an important original and abundant coniferous tree species whose wood was used for a wide range of purposes in the Czech Republic and throughout the Central region of Europe. This species lives for 500 to 800 years, growing to a height of 50 m and a diameter of 100 cm.

Several potential substitute species from other geographic areas have been identified to replace the silver fir (Podrázský et al. 2013). The final selection was a North American species, Grand fir (Abies grandis /Douglas/ Lindl.). The original habitat of A. grandis is the Northwest coast of North America. It reaches a height of 76 m and a diameter of 152 cm, and lives for approximately 250 years. It was introduced to the region of Central Europe as a prospective tree species to be planted for production of lumber, and has also been introduced as an ornamental tree in Hawaii and in Europe (St. John 1973; Otto 1982; Foiles et al. 1991; Alden 1997; Klinka 2007). In Germany, Grand firs have been introduced from North America and have a lot of economic value with their potential to raise the production of wood in domestic forests due to drought tolerance and ecological compatibility (Friedrich 1981; Nörr 2004).

Several experiments conducted at forestry sites in the Czech Republic have focused on the evaluation of growth, production of wood, and impact on the surrounding environment; results showed that Grand firs have the potential to replace domestic wood species and to contribute to forestry in the region (Podrázský and Remeš 2009; Fulín et al. 2013; Salem et al. 2013). There were pilot studies in neighboring countries to evaluate the characteristics of A. grandis wood (Hapla et al. 2013), but no such studies are currently taking place in the Czech Republic where the species composition of coniferous trees in the region is very poor.

Many studies have reported that A. grandis has a quick growing mass yield, but with low density values, and can be effective in industrial applications (Hapla 2006; Hof et al. 2008; Mitze 2010; Vos and Kharazipour 2010; Lukašek et al. 2012). The timber, regarded as weaker and less resistant to decay than many other species and susceptible to bacterial infections in wet-wood, is used primarily as a source of pulpwood (Burns and Honkala 1990; Alden 1997). Wagenführ (2007) reported that the wood density is 450 kg/m³ and the compression strength value is 47 MPa; the wood is described as moderate to moderately low in strength, stiffness, shock resistance, and nail withdrawal.

Mechanical properties of wood are significant indicators of wood quality from the viewpoint of its use for construction purposes. Strength properties are closely related to the density of the wood, and several studies reported the correlation between the density and strength properties (Barnett and Jeronimidis 2003; Sonderegger et al. 2008). Also, density is one of the basic indicators of wood quality and used as a criterion of strength grading, depending on the vertical and horizontal position in the stems (Panshin and De Zeeuw 1980; Salem et al. 2013).

This study is the first report on the strength properties as well as the density of A. grandis wood from two locations in the Czech Republic. The evaluation was performed with consideration of the vertical and horizontal positions and growing site.

EXPERIMENTAL

Materials

Site descriptions and sample preparation

The sampling began in 2013, and all the measurements were completed by the end of August 2014. At the first location (Site 1), A. grandis trees are located close to the village of Kostelec nad Černými lesy (49° 59′ 39″ N, 14° 51′ 20″ E, latitude 49.994167, longitude 14.855556) situated 25 to 50 km south-east of Prague; the area is an intermediate warm and intermediate wet region. The location is characterised by an average annual temperature of 8.14 °C, average total annual precipitation of 662.6 mm, an average growing season of 150 to 160 days, and pseudogley soils. Individual sites were distributed between elevations of 325 and 430 metres a.s.l. Tree species composition at the site was as follows: Norway spruce 40%, European beech 20%, Grand fir 20%, and European larch 20%. The descriptions of the localities have been previously reported by Podrázský and Remeš (2009) and Tauchman et al. (2010). The forest stands in this region are the property of the Czech University of Life Sciences and represent a considerable extent of the plot used for the research activities of the Faculty of Forestry and Wood Sciences.

The second location (Site 2) is located at Kynšperk nad Ohří (50° 7′ 8″ N, 12° 31′ 59″ E, latitude 50.118889, longitude 12.533056). Age-felled sample trees ranged from 35 to 45 years. Tree diameters ranged from 27 to 37 cm, with heights in the range of 24 to 30 m. This area is an intermediate warm and intermediate wet region characterised by an average annual temperature of 7 to 8°C, an average total annual precipitation of 550 to 700 mm, and an average growing season of 140 to 160 days. The site is situated at the elevation of 470 metres a.s.l. Tree species composition at the site was as follows: spruce 60% and Grand fire 40%. The all stands were regularly managed (e.g. thinning) in accordance with the forest management plan (10-years period).

From each tree stem, three sections 150 cm long ((bottom (1), middle (2), and top (3) sections)) were taken from each tree, as described previously (Langum et al. 2009; Lukašek et al. 2012), to evaluate the impact of vertical and horizontal positions in the stem. The sections represent different vertical positions in the trunk. When acquiring the specimens, the initial orientation in the plants was considered in terms of horizontal position (Sonderegger et al. 2008).

The sections were numbered (1, 2, 3, 4, and 5) from pith to bark for recognition of the horizontal position. The preparation of test samples and subsequent wood testing were done in accordance with the standard method ČSN 49 0101 (1980) in the laboratory with controlled temperature and relative humidity. The mechanical and wood density tests were conducted at a moisture content (MC) of 12% according to ČSN 49 0103 (1979) and ISO 3131 (1975).

Methods

Mechanical properties

Bending strength for 486 clear samples with dimensions of 20 mm × 20 mm × 300 mm was determined in accordance with ČSN 49 0101 (1980). The samples were conditioned in a controlled room (20 °C and 65% relative humidity) according to ČSN 49 0103 (1979) until the MC reached equilibrium. At 12% MC, the wood density (2485 samples) was measured according to ČSN 49 0108 (1993). The density was determined using the following formula,

 (1)

where ρ is the density of the wood, m is the mass of a test piece (g), and a, b, and l are the dimensions of the test piece (mm).

The bending strength was measured according to the following formula (ČSN 49 0115),

 (2)

where F_max is the maximum load (N), l is the distance between the two supports (mm), h is the height of the test piece (mm), and b is the width of the test piece (mm).

Compression strength (924 samples) was evaluated on test specimens with dimensions of 20 mm × 20 mm × 30 mm according to the following formula (ČSN 49 0110),

 (3)

where F_max is the maximum load (N) and a and b are the transverse dimensions of the sample (mm).

Impact strength (386 samples) was assessed with respect to vertical position only on samples with dimensions of 20 mm × 20 mm × 300 mm using the following formula (ČSN 49 0117),

 (4)

where Q is the energy expended to break the sample (J) and b and h are the sample dimensions in the radial and tangential directions (cm), respectively.

Statistical analysis

The mechanical properties and density values of A. grandis wood, with respect to the vertical and horizontal positions and the growing sites, were statistically analyzed using the general linear model (GLM) procedure in SAS version 8.2 (2001). A comparison among the least square (LS) means of factors and levels with 95% confidence intervals (CI) was performed using Duncan’s multiple-range test to identify significant differences and to compare the means between the obtained values. Linear correlations were used to evaluate the dependence of the mechanical properties on the density of wood from both sites.

RESULTS AND DISCUSSION

Data presented in Tables 1 and 2 shows that the average density of the Grand fir wood was 410.267 kg/m³; this value is close to the value from the trees growing in their original geographic area (449 kg/m³) (Alden 1997). The compression and bending strength values (39.577 and 78.119 MPa, respectively) were higher than the values reported from the original area (36.5 and 68 MPa, respectively) (Alden 1997), and the impact strength value was 4.186 J/cm², which is similar to values reported for other softwood species. Lukašek et al. (2012) reported that the density at 12% MC of A. grandis growing in the Czech Republic was 405 kg/m³, and Hapla et al. (2014) reported that the oven dry density varied with different height in compression wood, sapwood, and heartwood, i.e., at the height of 1.5 m the values were 0.449 g/cm³ (compression wood), 0.354 g/cm³ (heartwood), and 0.457 g/cm³ (sapwood).

The data calculated from the two sites (Table 1) indicated that there were variations in the values in the studied variables for both sites, and the variation were with respect to tree age, wood anatomy, environmental and soil conditions, silvicultural practice (Bektas et al. 2003; Miranda et al. 2007), and the position of the test piece within the tree (de Palacios et al. 2008).

Table 1. Descriptive Statistics for Density and Selected Mechanical Properties of A. grandis Wood

Table 2. Comparison among the Values of Selective Properties from Commercial Softwoods and Values from Grand Fir in the Present Study

^aData from Wagenführ (2007); ^bdata from Alden (1997)

Effect of Growing Site and Position of Wood Samples on Wood Density of A. grandis

The variations in density in wood as affected by vertical position (bottom, middle, and top sections) and growing site are shown in Fig. 1 and Table 3. The site, vertical position, and interaction between them significantly (P < 0.001) affected the density values. Additionally, the density values at site 2 were higher than those from site 1, and the value from the bottom vertical position in the two sites was higher than the values from the middle and top positions. The density was highest at the bottom (Hapla et al. 2013). Furthermore, the values from the middle position at the two sites were lower than those from the top position, but the difference was not significant.

With respect to the horizontal positions (Table 3 and Fig. 2), there was a clear trend of increasing density values from pith to bark, with a highly significant (P < 0.001) effect of horizontal position as well as the interaction between the site and horizontal position. On the other hand, the differences in wood density values between the two sites were not significant (P = 0.59).

Table 3. A. grandis Density (kg/m³) with Respect to Site and Vertical and Horizontal Positions

Table 4. Bending Strength (MPa) of A. grandis Wood with Respect to Site and Vertical and Horizontal Positions

Effect of Growing Site and Position of Wood Samples on Mechanical Properties of A. grandis

Figure 3 (vertical position) and Fig. 4 (horizontal position) show the bending strength values of A. grandis wood as affected by the two sites. Both the site and position of wood had a highly significant (P < 0.001) effect on bending strength. On the other hand, the interaction between the site and vertical or horizontal position was not significant. Furthermore, the highest values of bending strength (vertical position) were observed in the bottom positions from sites 2 and 1, with values of 86.292 and 83.233 MPa, respectively (Table 4).

With respect to horizontal position, the height values of bending strength were shown in section number 5, in sites 2 and 1 with values of 105.583 and 101.919 MPa, respectively. The bending strength increased from pith to bark and from top to bottom of the tree stem (Table 4).

Compression strength, as shown in Fig. 5, was significantly affected by vertical position (P<0.001), but not by site (P = 0.29) or the interaction between vertical position and growing site (P = 0.15). The bottom sections from the two sites were observed to have the highest compression strength, with values of 40.573 MPa and 41.265 MPa, respectively (Table 5). The compression strength was significantly (P < 0.001) affected by horizontal position, growing site, and the interaction between them (Fig. 6). The values uniformly increased from pith to bark (Table 5).

Table 5. Compression Strength (MPa) of A. grandis Wood with Respect to Site and Vertical and Horizontal Positions

For the impact strength, we measured only the effect of vertical position, which showed that the bottom position of wood had a significant effect (P < 0.001) on the measured values, whereas neither the growing site (P = 0.85) nor the interaction between vertical position and growing site (P = 0.35) had a significant effect (Fig. 7). The highest values were observed in the bottom section at both sites (4.384 and 4.571 J/cm², respectively), but these values were not significantly different (Table 6). Some of the above results are similar to those found in the study of González-Rodrigo et al. (2013) with respect to the variation throughout the tree stem of the wood of A. alba, the study of Machado and Cruz (2005) on Maritime pine, and the study of Antony et al. (2011) on planted loblolly pine in the United States.

Fig. 7. Effect on the impact strength of vertical position of A. grandis wood with growing site. Vertical bars denote confidence intervals of 0.95. Means with the same letters are not significantly different at P < 0.05 according to Duncan’s multiple-range test

Table 6. Effect of Interaction between Site and Vertical Position on the Values of Impact Strength (J/cm²)

Correlation between Density and Selected Mechanical Properties of A. grandis Wood

To determine the value and benefits of wood as a bioresource for the production of wood-based material, the relationships among the density and various mechanical properties of A. grandis wood was found by determining the regression equations and correlation coefficients (r). Several studies have reported that wood quality and mechanical and physical properties of wood can be indicated by wood density (Niemz 1993; Niemz and Sonderegger 2003; Esteban et al. 2009; Lukášek et al. 2012). Additionally, density can influence harvesting and transport costs, strength properties, and the yield in the paper and fiber industry (Hapla et al. 2014).

In the present study, 38 correlations among the density and the bending and compression strength values (from the two sites and all vertical and horizontal wood sampling positions), as well as impact strength (two sites and vertical position), were measured.

At the first site, the correlation coefficients for density and bending strength (Table 7) ranged from r = 0.35 (horizontal position 1) to r = 0.93 (vertical bottom position). The samples from the middle position showed a very good correlation with the density (r = 0.89). Additionally, the samples from horizontal position 3 had a good relationship with density (r = 0.74). At site 2, high correlation coefficient values (r = 0.91, 0.89, and 0.85) were observed between density and samples from horizontal position 3, the bottom vertical position, and horizontal position 4, respectively.

Table 7. Correlation between Bending (MPa) and Density (kg/m³) at Different Vertical and Horizontal Positions for Two Sites

Y, Bending strength (MPa); X, Density (kg/m³).

Compression strength values were highly correlated (Table 8) with density at vertical positions (bottom and middle) at the first site (r = 0.98), followed by horizontal positions 3 (r = 0.89) and 4 (r = 0.86). At the second site, a good correlation was observed between values from the bottom vertical position (r = 0.90) and horizontal position 4 (r = 0.90).

Table 8. Correlation between Compression Strength (MPa) and Density (kg/m³) at Different Vertical and Horizontal Positions for Two Sites

Y, Compression strength (MPa); X, Density (kg/m³).

Density and impact strength had moderate or poor correlations (Table 9) in the vertical position, although a good value was shown for the middle position (r = 0.87) from site 2. The low correlations could be explained by the differences between the density of sapwood and heartwood like reported in the study of Hapla et al. (2013), who demonstrated that juvenile wood was the reason for the significant difference between sapwood and heartwood, which has lower cell wall / lumen ratio (Zobel and van Buijtenen 1989). Also, in vertical position the correlation was highly significant, and this result is in agreement with Risi and Zeller (1960), Stern (1963), and Olesen (1973), where the density is normally decreasing with height in the case of softwoods.

Table 9. Correlation between Density (kg/m³) and Impact Strength (J/cm²) at Different Vertical Positions for Two Sites

Y, Impact strength (MPa); X, Density (kg/m³).

Generally, the vertical bottom position and horizontal positions 3 and 4 in the tree stem had good correlations with density and bending and compression strength. On the other hand, the correlation between density and impact strength was unconvincing. Additionally, the variations could be related to the compression wood, which was previously reported that the density was higher in case of sapwood (Esteban et al. 2009; Lukášek et al. 2012; Hapla et al. 2013). Furthermore, Giant fir has enormous growth dynamic, which procures an eccentric secondary thickness and leads to the formation of compression wood (Riebel 1994).

Previously, Cown (1992), Houllier (1993), Houllier et al. (1995), and Zhou et al. (2008) found that there has been an urgent need for management tools to integrate both growth and wood quality information, leading to a new generation of more detailed models; these models have been developed for fast-growing species of coniferous plantations in different regions around the world (e.g., Pseudotsuga menziesii, western-hemlock, Tsuga heterophylla, Radiata pine, and Scots pine), as well as for Norway spruce (Behrendt et al. 2007; Dohrenbusch and Bolte 2008; Spellmann and Kehr 2008; Müller et al. 2009).

In the present study, we attempted to determine details concerning the relationship between the density and selected mechanical properties for an introduced coniferous species in the Czech Republic to ensure a long-term supply for wood processing industries. The results provide practical data for the timber-oriented sorting of Grand fir logs. The vertical bottom sections of the stems could be suitable for lumber and other wood products (particleboard, paper, fiberboard, etc.) because of the significant correlations among the density and mechanical strengths.

The differences obtained in the mechanical properties of A. grandis may be due to the limited number of tested wood specimens with considering the local variability of the species, where some variations were found to have resulted from specific conditions of the two studied sites (Brown et al. 1952; Blanco et al. 1997). Further studies on mechanical properties from other stands of A. grandis from the Czech Republic will be useful for the generality of the obtained results form A. grandis.

CONCLUSIONS

1. The differences in the mechanical properties of A. grandis may be due to the limited number of tested wood specimens when considering the local variability of the species.
2. The average values of mechanical properties were compression strength (39.577 MPa), bending strength (78.119 MPa), and impact strength (4.186 J/cm²) with a density of 410.267 kg/m³.
3. The highest correlations of the strength characteristics with density were shown in the case of bending at the vertical bottom position (r = 0.95) and for compression strength at vertical positions (bottom and middle) at the first site (r = 0.98). The impact strength showed moderate or poor correlations with the vertical position, although a good value was shown for the middle position (r = 0.87).
4. The site, vertical position, and interaction between them all significantly (P < 0.001) affected the density. The site and position of wood had a highly significant (P < 0.001) effect on bending strength. Compression strength was significantly affected by vertical position, but not by site (P = 0.29).
5. As general results, the vertical bottom position and horizontal positions 3 and 4 in the tree stem had good correlations among the density and bending and compression strengths. On the other hand, the correlation between the density and impact strength was unconvincing.

ACKNOWLEDGMENTS

This project was supported by the Internal Grant Agency of the Faculty of Forestry and Wood Sciences of the Czech University of Life Sciences in Prague. We also thank the Forest Enterprise in Kostelec nad Černými lesy for providing the material.

REFERENCES CITED

Alden, H. A. (1997). “Softwoods of North America,” Gen. Tech. Rep.-102US, Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI, http://www2.fpl.fs.fed.us/publications/fplgtr102.pdf .

Antony, F., Jordan, L., Schimleck, L. R., Clark III, A., Souter, R A., and Daniels, R. F. (2011). “Regional variation in wood modulus of elasticity (stiffness) and modulus of rupture (strength) of planted loblolly pine in the United States,” Can. J. For. Res. 41(7), 1522-1533. DOI: 10.1139/x11-064

Barnett, J. R., and Jeronimidis, G. (2003). Wood Quality and its Biological Basis, Blackwell Publishing, Oxford.

Behrendt, S., Henseling, C., Erdmann, L., Knoll, M., and Rupp, J. (2007). “Trendreport: Zukunftstrends für das Bauen mit Holz,” Paperreihe des Holzwende 2020plus-Projektes, Institut für Zukunftsstudien und Technologiebewertung, Eigenverlag, Berlin, http://www.holzwende2020.de/custom/user/Basis-Studie/Trendreport_IZT.pdf.

Bektas, L., Alma, M. H., As, N., and Cundogan, R. (2003). “Relationship between site index and several mechanical properties of Turkish Calabrian pine (Pinus brutia Ten.),” Forest Prod J. 53(2), 27-31.

Blanco, E., Casado, M. A., Costa, M., Escribano, R., García, M, Génova, M., Gómez, A., Gómez, F., Moreno, J. C., Morla, C., Regato, P., and Sainz, H. (1997). “Los bosques ibéricos. p. 572. 1st ^Ed,” Planeta, Barcelona, España.

Brown, H. P., Panshin, A. J., and Forsaith, C. C. (1952). Textbook of Wood Technology: The Physical, Mechanical and Chemical Properties of the Commercial Woods of the United States, 2: 783. McGraw-Hill, New York (NY), USA.

Burns, R. M., and Honkala, B. H. (1990). “Silvics of North America: 1. Conifers; 2. Hardwoods,” Agriculture Handbook 654, U.S. Department of Agriculture, Forest Service, Washington, DC.

Cown, D. (1992). “Modelling the impacts of site and silviculture: The New Zealand experience,” IUFRO All Division 5 Conference Forest Products, Nancy, France, 23-28 Aollt 1992, ARBOLOR Cd., pp. 297-298.

ČSN 49 0101. (1980). “Wood. General requirements for physical and mechanical testing,” Czech Office for Standards, Metrology and Testing (ÚNMZ), Prague, Czech Republic.

ČSN 49 0103. (1979). “Wood. Determination of moisture content at physical and mechanical testing,” Czech Office for Standards, Metrology and Testing (ÚNMZ), Prague, Czech Republic.

ČSN 49 0108. (1993). “Wood. Determination of the density,” Czech Office for Standards, Metrology and Testing (ÚNMZ), Prague, Czech Republic.

ČSN 49 0110. (1977). “Wood. Determination of compression strength parallel to the grains” (in Czech), Czech Office for Standards, Metrology and Testing (ÚNMZ), Prague, Czech Republic.

ČSN 49 0115. (1979). “Wood. Determination of bending strength,” Czech Office for Standards, Metrology and Testing (ÚNMZ), Prague, Czech Republic.

ČSN 49 0117. (1980). “Wood. Determination of impact strength,” Czech Office for Standards, Metrology and Testing (ÚNMZ), Prague, Czech Republic.

de Palacios, P., Esteban, L. G., Guindeo, A., Fernandez, F. G., Canteli, A. F., and Navarro, N. (2008). “Variation of impact bending in the wood of Pinus sylvestris L. in relation to its position in the tree,” Forest Prod. J. 58(3), 55-60.

Dohrenbusch, A., and Bolte, A. (2008). “Forest plantations,” in: Wood Production, Wood Technology and Biotechnological Impacts, U. Kües (ed.), Universitätsverlag, Göttingen, pp. 646.

Esteban, L. G., De Palacios, P., García, F., and Ovies, J. (2009). “Mechanical properties of wood from the relict Abies pinsapo forests,” Forest Prod. J. 59(10), 72-78. DOI: 10.13073/0015-7473-59.10.72

Foiles, M. W., Graham, R. T., and Olson, D. F. (1991). “Grand fir,” Silvics of North America: Conifers,United States Forest Service, pp. 52-68.

Friedrich, E. (1981). “Wachstum, Aufbau und Substanzproduktion von dreijährigen Abies grandis (Lindley) aus 21 Herkünften,” in: Neuere Grundlagen für den Anbau von Abies grandis, R. Röhrig (ed.), J. D. Sauerländer’s Verlag, Frankfurt a. Main. Schriften aus der Forstlichen Fakultät der Universität Göttingen und der Niedersächsischen Forstlichen Versuchsanstalt, Bd. 71, S.31-50.

Fulín, M., Remeš, J., and Tauchman, P. (2013). “Growth and production of Grand fir (Abies grandisLindl.) compared with other tree species,” Zprávy Lesnického Výzkumu 58(2), 186-192.

González-Rodrigo, B., Esteban, L. G., de Palacios, P., García-Fernández, F. and Guindeo, A. (2013). “Variation throughout the tree stem in the physical-mechanical properties of the wood of Abies albaMill. from the Spanish Pyrenees,” Madera y Bosques 19(2), 87-107.

Hapla, F. (2006). “Use- and wood product-orientated investigation on Abies grandis with different growth dynamics – An experimental design,” In: IUFRO-Division 5 (Hg.) Proceedings of the 5th International Symposium “Wood Structure and Properties”. IUFRO, Zvolen, Slovakia, 51-52.

Hapla, F., Kubalek, S., Bak, M., and Németh, R. (2013). “Timber grade oriented analysis of Abies grandis trees’ oven dry density with different growth rates. Part I: Experimental design,” Wood Res.58(3), 361-368.

Hapla, F., Kubalek, S., Bak, M., and Németh, R. (2014). “Timber grade oriented analysis of Abies grandis trees’ oven dry density with different growth rates. Part II: Effect of the trees’ social position in the forest on the variability of oven dry density,” Wood Res. 59(2), 273-282.

Hof, C. H., Kielmann, B. C., and Hapla, F. (2008). “Verwendungsorientierte Untersuchungen am Schnittholz der Abies grandis,” Holztechnologie 49(6), 7-11.

Houllier, F. (1993). “Modelling ring width distribution in the tree in relation to silvicultural treatment (Norway spruce),” Subtask report of the EEC project Silvicultural Control and Non-Destructive Assessment of Timber Quality of Plantation Grown Spruces and Douglas-Fir, ENGREF, Nancy, France.

Houllier, F., Leban, J.-M., and Colin, F. (1995). “Linking growth modelling to timber quality assessment for Norway spruce,” For. Ecol. Manage. 74(1-2), 91-102. DOI: 10.1016/0378-1127(94)03510-4

ISO 3131 (1975). “Wood. Determination of density for physical and mechanical tests,” International Organization for Standardization, Geneva, Switzerland.

John, H. St. (1973). List and summary of the flowering plants in the Hawaiian Islands. Pacific Tropical Botanical Garden Memoir Number 1. 519 pages. Cathay Press Limited, 31 Wong Chuk Hang Road, Aberdeen, Hong Kong, Lawai, Kauai, Hawaii, August 30, 1973. Journal of Botanical Taxonomy and Geubotany, Feddes Repertorium, 86(3), page 199. DOI: 10.1002/fedr.19750860304

Klinka, K. (2007). “Die Grosse Kustentanne (Abies grandis Lindl.) in Kanada und in den USA,” Forst und Holz 62(7), 10-13.

Langum, C. E., Yadama, V., and Lowell, E. C. (2009). “Physical and mechanical properties of young-growth Douglas-fir and western hemlock from western Washington,” For. Prod. J. 59(11/12), 37-47. DOI: 10.13073/0015-7473-59.11.37

Lukašek, J., Zeidler, A., and Barcik, Š. (2012). “Shrinkage of grand fir wood and its variability within the stem,” Drvna Indust. 63(2), 121-128. DOI: 10.5552/drind.2012.1140

Machado, J. S., and Cruz, H. P. (2005). “Within stem variation of Maritime Pine timber mechanical properties,” Holz Roh Werkst. 63(2), 154-159. DOI: 10.1007/s00107-004-0560-4

Ministry of Agriculture (2012). “Report on the forests state and forest management of the Czech Republic” (in Czech), Prague, Czech Republic.

Miranda, I., Gominho, J., Lourenço, A., and Pereira, H. (2007). “Heartwood, extractives and pulp yield of three Eucalyptus globulus clones grown in two sites,” Appita J. 60(6), 485-488.

Mitze, H. (2010). “Ein unterschatzer Nordamerikaner: Küstentanne Forstwirtschaft,” Land & Forst.26, 66-67.

Müller, G., Schöpper, C., Vos, H., Kharazipour, A., and Polle, A. (2009). “FTIR-ATR spectroscopic analyses of changes in wood properties during particle- and fibreboard production of hard- and softwood trees,” BioResources 4(1), 49-71. DOI: 10.15376/biores.4.1.49-71

Niemz, P. (1993). Physik des Holzes und der Holzwerkstoffe, DRW- Verlag, Weinbrenner.

Niemz, P., and Sonderegger, W. (2003). “Untersuchungen zur Korrelation ausgewahlter Holzeigenschaften untereinander unt mit der Rohdichte unter Verwendung von 103 Holzarten,” Schweizerische Zeitschrift fur Forstwesen 154(12), 489-493. DOI: 10.3188/szf.2003.0489

Nörr, R. (2004). “Vom Exoten zur Wirtschaftsbaumart: 175 Jahre Douglasienanbau in Deutschland,” LWF Aktuell 45, 7-9.

Olesen, P. O. (1973). “The influence of the compass direction on the basic density of Norway spruce (Picea abies L.) and its importance for sampling for estimating the genetic value of plus trees,” For. Tree Impr. Arbor, Nob Horsholm, Denmark, 58 pp.

Otto, H.-J. (1982). “Measures to reduce forest fire hazards and restoration of damaged areas in Lower Saxony,” in: Forest Fire Prevention & Control: Forestry Sciences: Proc. of an International Seminar Organized by the Timber Committee of the U.N., The Hague, Netherlands, W. M. Nigholt (ed.), Springer Netherlands, 7; 173-179. DOI: 10.1007/978-94-017-1574-4_20

Panshin, A. J., and De Zeeuw, C. (1980). Textbook of Wood Technology, McGraw-Hill, New York.

Podrázský, V., and Remeš, J. (2009). “Soil-forming effect of grand fir (Abies grandis [Dougl. ex D. Don] Lindl.),” J. For. Sci. 55(12), 533-539.

Podrázský, V., Čermák, R., Zahradník, D., and Kouba, J. (2013). “Production of Douglas-fir in the Czech Republic based on national forest inventory data,” J. For. Sci. 59(10), 398-404.

Risi, J., and Zeller, E. (1960). “Specific gravity of the wood of black spruce (Picea mariana Mill BSP) grown on a Hylocomium-Cornus site type,” Laval University Forestry Research Foundation Québec, Canada, Contribution 6: 70 pp.

Riebel, H. (1994). “Über einige Holzeigenschaften der Großen Küstentanne (Abies grandis (Douglas) Lindley) aus südwestdeutschen Anbauten,” Heft 177, in: Mitteilungen der Forstlichen Versuchsanstalt Baden-Württemberg, 277 pp.

Salem, M. Z. M., Zeidler, A., Böhm, M., and Srba, J. (2013). “Norway spruce (Picea abies [L.] Karst.) as a bioresource: Evaluation of solid wood, particleboard, and MDF technological properties and formaldehyde emission,” BioResources 8(1), 1199-1221. DOI: 10.15376/biores.8.1.1199-1221

SAS (2001). User’s Guide: Statistics (Release 8.02), SAS Institute, Cary, NC.

Sonderegger, W., Mandallaz, D., and Niemz, P. (2008). “An investigation of the influence of selected factors on the properties of spruce wood,” Wood Sci. Technol. 42(4), 281-298. DOI: 10.1007/s00226-007-0173-2

Spellmann, H., and Kehr, I. (2008). “The wood supply in the world, Europe, Germany, and Lower Saxony,” in: Wood Production, Wood Technology and Bio-Technological Impacts, U. Kües, (ed.), Universitätsverlag, Göttingen, pp. 43-55.

Stern, K. (1963). “Einfluss der Höhe am Stamm auf die Verteilung der Raumdichte des Holzes in Fichtenbeständen,” Holzforschung 17(1), 6-12. DOI: 10.1515/hfsg.1963.17.1.6

Tauchman, P., Hart, V., and Remeš, J. (2010). “Srovnani produkce porostu douglasky tisoliste (Pseudotsuga menziesii / Mirbel/ Franco) s porostem smrku ztepileho (Picea abies L. Karst.) a stanovištně původnim smišenym porostem středniho věku na uzemi ŠLP v Kostelci nad Černymi lesy,” Zpravy Lesnickeho Vyzkumu 55(3), 187-194.

Vos, H., and Kharazipour, A. (2010). “Eigenschaften von leichten, industriell hergestellten Spanplatten aus Abies grandis (Küstentanne),” Forst und Holz 65(1), 26-30.

Wagenführ, R. (2007). Holzatlas. Fachbuchverlag, Leipzig, 6^th edition, pp.707.

Zhou, M., Liang, J., and Buongior, J. (2008). “Adaptive versus fixed policies for economic or ecological objectives in forest management,” For. Ecol. Manage. 254(2), 178-187. DOI: 10.1016/j.foreco.2007.07.035

Zobel, B. J., and van Buijtenen, J. P. (1989). Wood Variation. Its Causes and Control, Springer-Verlag, Berlin Heidelberg. Pp 82-100.

Article submitted: September 5, 2014; Peer review completed: November 9, 2014; Revised version received and accepted: November 18, 2014; Published: December 7, 2014.