EFFECT OF SPACING ON SOME MECHANICAL PROPERTIES OF NARROW LEAVED ASH (Fraxinus angustifolia) WOOD

In this study, conducted to test the effect of spacing on wood quality; the effect of four different spacing types, applied in Adapazarı Süleymaniye plantation (Region 1; 3x2 m; Region 2; 3x2,5 m; Region 3; 3,75x3,75 m; Region 4; 4x4 m), on some mechanical properties of narrow leaved ash (Fraxinus angustifolia) have been studied. In the present study, some mechanical properties such as the compression strength parallel to grain, tensile stress perpendicular to grain, bending strength, impact bending strength and modulus of elasticity were determined. As a result, the ash wood, grown in region 4 with a wide range of planting, has high mechanical properties. However, when analyzed in terms of wood quality characteristics, it has been found that spacing in region 1 (2x3 m) is more suitable for applications of ash plantations.


INTRODUCTION
Geographical spread of ash begins from South East Europe, and reaches to Turkey, Iran and Turkestan.This species is more common in different forest regions in our country.Süleymaniye Forest at the stuffed areas at the mouth of Sakarya River near Adapazarı and Çilinkoz Forest near Demirköy are the most beautiful forests of this type.They have been formed from the 1940s to the present day as a plantation forest (Sahin 2013).
Spacing is a determinative and important issue for the quality of the forest to be grown.Additionally, it determines the cost of plant and which industry the tree material is used in.Spacing also determines the degree that trees benefit from the habitat.Different spacing types have an impact on density and strength characteristics.In wide-spaced planting, density in young-leaved trees with ring vessels is at the maximum level, consequently the resistance properties increase.Density decreases in coniferous trees when spacing is applied.The fact that annual rings are large in the first years increases the portion of young wood.As young wood is of low density, it will cause a decrease in density depending on its presence in the material (Haygreen and Bowyer 1996).
Since the narrow-leaved ash (Fraxinus angustifolia) is a fast-growing species, and because of the industrial value of its wood; the interest in this species especially in European countries has greatly increased.Lately, studies on especially this species have gained momentum (Fraxigen 2005).
The common presence of ash (Fraxinus excelsior), which has an important place in forest trees in Europe, is seen as a great opportunity (Kerr 1995).Many European countries are intensively breeding this species in order to produce high quality timber.So, the concern for silviculture, breeding and gene conservation activities of ash has recently increased in many countries (Kerr 1995, Pliura 1999, Eriksson 2001, Kerr 2003, Fraxigen 2005).
Although narrow-leaved ash is common throughout Europe, it is mostly neglected and rarely studied (Piotto and Piccini 1998).In this context, the effects of different spacing and culture care methods on the development of narrow-leaved ash (Fraxinus angustifolia) have been investigated (Carus and Çiçek 2007).
On the other hand, many studies have been conducted on "the effect of spacing on narrow-leaved ash plantations, soil properties, stand structures and silvicultural measures'' in Süleymaniye region, it is highlighted that ash trees with tight spacing form better quality and smooth body structures (Çiçek and Yilmaz 2002(Çiçek and Yilmaz , Çiçek 2004(Çiçek and Yilmaz , Çiçek 2010)).
In this study; the effects of four different spacing (3x2 m in Region 1; 3x2,5 m in the Region 2; 3,75x3,75 m in the Region 3 and 4x4 m in the Region 4) applied in Adapazarı Süleymaniye plantations in Turkey on some mechanical properties of narrow-leaved ash (Fraxinus angustifolia) wood are investigated.

Sample Tree Selection and Acquisition of the Sections
In the selection of the experiment field and experiment trees of narrow-leaved ash (Fraxinus angustifolia Vahl.), TS 4176 (1984) standard is used as a base.For the specified purpose, the spacing of 4x4 m; 3,70x3,70 m; 3x2,5 m; 3x2 m were determined in Adapazarı-Süleymaniye region, and 4 pieces of sample trees, corresponding to the average breast diameter that represents each group, having no cracks and showing no abnormal peak forms, have been cut with a chainsaw.

Preparation of Test Samples
Two cm wide strips were cut in North-South and East-West directions from the 15 cm sections taken from sample trees and cross-sectional samples were determined by drawing 2 cm lines on these strips.Air-dry density samples of 20 x 20 x 30 mm were prepared by determining in 30 mm sections parallel to the fibers.It was taken into consideration that the samples did not contain defects such as cracks, knots and so on.The defective samples were replaced with new ones.
Determination of air dry density has been made by TS 2472TS (1976)).Of the mechanical properties; experiments of compression strength parallel to grain were conducted in accordance with TS 2595 (1977), bending strength in accordance with TS 2474 (1976) principles, modulus of elasticity on bending in accordance with TS 2478 (1978) principles, impact bending strength in accordance with TS 2477 (1976) principles, tensile strength perpendicular to grain in accordance with TS 2476 (1976) standard.Some mechanical strength test was given in Figure 1.Additionally, quality value of compression strength parallel to grain, bending quality and robustness and impact bending strength quality value were also calculated.Statistical evaluation was performed with SPSS software.

RESULTS AND DISCUSSION
Air-Dry Density Air-dry density values were calculated on 374 samples from four experiment sites.Air-dry density values and statistical evaluation results calculated from narrow-leaved ash (Fraxinus angustifolia) samples taken from 4 different spacing are shown in Table 1.Differences in the arithmetic average were detected, in order to determine which factor caused this difference, a variance analysis was performed.

Table 1. Air-dry density values (kg/m 3 ).
According to the results of variance analysis, differences between regions were statistically significant at 0,001 confidence level.Then, according to the Duncan test, given in Table 1, a significant different was not found between region 3 and region 2 in terms of air-dry density.The trees growing in regions 1 and 4 not only differ statistically from each other but also from those grown in regions 3 and 2.
Average air-dry density was found as 679 kg/m 3 in region 1 (3x2 m), 691 kg/m 3 in region 2 (3x2,5 m); 724  kg/m 3 in region 3 (3,7x3,7 m) and 759 kg/m 3 in region 4 (4x4 m).Region 4, with the largest spacing, belongs to the group of trees with having the highest air-dry density of all the other regions.The overall average was found to be 713 kg/m 3 .These results are in agreement with those of previous studies using similar wood types (Yalcin and Sahin 2015, Govorcin et al. 2009, Forest Product Laboratory 2010).In wide-spacing, density is maximum in trees with ring vessels, thus, their resistance properties increase (Haygreen andBowyer 1996, Bozkurt andErdin 1997).
According to Bozkurt and Erdin (1990), classification of air-dry density is listed as; very light trees <290 kg/m 3 , light trees 300-490 kg/m 3 , medium weight trees 500-690 kg/m 3 , heavy trees 700-990 kg/m 3 and very heavy trees >1000 kg/m 3 .Air-dry density values and classes are shown in table 2 of according to spacing.The overall average of narrow-leaved ash belongs to the group of ''heavy'' trees.
Table 2. Air-dry density values and classes according to spacing.

Compression Strength Parallel to Grain
Descriptive data on compression strength parallel to grain (MPa) is given in Table 3.Furthermore, whether there was a significant difference between regions was tested by analysis of variance; in the event of a difference, which group or groups it arose from was determined by the Duncan test.The statistical evaluation results for these are given in Table 3.

Table 3. Values of compression strength parallel to grain (MPa).
According to the results of the Duncan test given in Table 3, there is not a statistically significant difference between region 1, region 2 and region 3 in terms of compression strength parallel to grain, while there is no statistically significant difference between regions 2 and 3, however, it was found different from these three groups in region 4.In terms of spacing of compression strength parallel to grain values, they are 58,643; 57,41; 56,53; 62,7 MPa respectively.Compression strength was found maximum (62,7 MPa) in region 4 (4x4 m), and minimum (56,53 MPa) in region 3 (3,7x3,7 m).In wide spacing of trees with ring vessels; high resistance properties are considered normal and the resistance properties increase as a result of density increase (Haygreen andBowyer 1996, Bozkurt andErdin 1997).
According to Bozkurt and Erdin (1990); classes of compression strength parallel to grain are listed as < 20 MPa very small, 20-35 MPa small, medium 35-55 MPa, 55-85 MPa high and > 85 MPa very high.Average compression strength among the regions was found to be 58,8 MPa.According to this, narrow leaved ash belongs to the group of trees with a high compression strength parallel to grain (55-85 MPa).Region 4, with the largest spacing, belongs to the group of trees with "high" compression strength having the highest compression strength of all the other regions.Compression strength parallel to grain and its classification is given in Table 4.
Table 4. Values of compression strength parallel to grain and its classes for some species of trees.
The overall average of compression strength of narrow leaved ash is 58,8 MPa.With this value; its compression strength parallel to grain is higher than white ash, pine and ash but lower than those of common ash, beech and eucalyptus.

Values of Compression Strength Parallel to Grain
Static quality values of compression strength parallel to grain are given in Figure 2. Static quality values found by values of compression strength parallel to grain and air-dry density are 8,6 in region 1; 8,3 in region 2; 7,86 in region 3 and 8,25 in region 4 respectively.Bozkurt and Erdin (1997) states that when the static quality value for hardwood is <6, it has a "low" quality, when it is between 6,5-7,5; it has a "medium" quality, and when it is > 7,5; it has a "good" quality.Overall average of compression strength static quality value of narrow leaved ash was found to be 8,24.According to this classification; the overall average for narrow-leaved ash and the entire region belong to the "good" quality group.Static quality values are given for some species of trees in table 5.
Table 5. Static quality values of some tree species.
According to the general average; the quality value of narrow-leaved ash was found 8,24.Based on these results; the static quality value of beech-bodied maple is higher than that of sharp fruity ashen, but lower than those of Taurus cedar, common ash and Eastern beech.

Bending Strength
Descriptive statistics of values of bending strength are given in Table 6.There is no statistically significant difference between regions 2 and 3, however, average bending strength was found 117,1 MPa in region 1; 109,6 MPa in region 2; 105,7 MPa in region 3 and 130,3 MPa in region 4. Bending strength is maximum (130,3 MPa) in region 4 and minimum (105,7 MPa) in region 3.The overall average of narrow leaved ash samples is 115,7 MPa.Reason for obtaining a high resistance in the region 4 is the fact that wide spacing increase density in trees with ring vessels.

Table 6. Bending strength values (MPa).
According to Bozkurt and Erdin (1990); classes of bending strength are listed as <50 MPa "very small", 50-85 MPa "small", 85-120 MPa "medium" , 120-175 MPa "high" and > 175 MPa "very high".The overall average of bending strength of narrow-leaved ash samples is 115,7 MPa.According to this, in terms of the overall average of bending strength of narrow-leaved ash; there is no statistically significant difference between regions 2 and 3, however, belongs to the group of trees with "medium" values (85-120 MPa).Of these regions, region 4 is placed under the group with "high" bending strength with a value of 130,3 MPa.Bending strengths and their classes are given for some tree species in Table 7.
Table 7. Bending strengths and their classes of some tree species.
The overall average of bending strength of narrow-leaved ash samples is 115,66 MPa.According to this result, the bending strength of narrow-leaved ash is higher than those of eucalyptus, pine, white ash and ash; but lower than those of ash, beech and common ash.It is understood that the wood of narrow-leaved ash, having a "medium" general bending strength can be used in furniture, sports equipment, bridges and joists.

Quality and Strength in Bending
Values of bending quality and quality results are given in Figure 3. Average quality in bending was found 17,2 in region 1; 15,9 in region 2; 14,6 in region 3 and 17,1 in region 4.According to Bozkurt and Erdin (1990); classes of bending quality are listed as 10-15 "low", 15-20 "medium", 20-25 "high".Quality in bending was maximum in region 1 and minimum in region 3.The overall average quality in bending was found 16,2.Value of quality in bending was found "medium" (15-20) in all regions and for the overall average.
Overall average of bending strength is 1,95; and it belongs to the class of "low" (1-2) strength.Strength in bending was highest in region 4 and lowest in region 3. Region 4, with a bending strength of 2,07; is in the "medium" (2-3) strength group.In addition to this, region 1, with a bending strength of 2,00 is both higher than the average and in the "middle" class.

Modulus of Elasticity
Descriptive statistics of modulus of elasticity are shown in Table 9.According to the results of the Duncan test, there is not a statistically significant difference between region 1, region 2 and region 3 in terms of modulus of elasticity, while there is no statistically significant difference between regions 2 and 3, however, it was found different from these three groups in region 4.

Table 9. Modulus of elasticity values (MPa).
Overall average of modulus of elasticity was 9601 MPa in region 1; 9556 MPa in region 2; 8847 MPa in region 3 and 11502 MPa in region 4. Modulus of elasticity was highest in region 4 (11502 MPa) and lowest in region 3 (8847 MPa).
According to Bozkurt and Erdin (1990); classes of modulus of elasticity are defined as <6000 MPa "very small", 6000-10000 MPa "small", 10000-13000 MPa "medium", 13000-16000 MPa "high" and >16000 MPa "very high".The overall average of modulus of elasticity of narrow leaved ash was found 9877 MPa.Narrow leaved ash belongs to group of trees with a "small" overall average of modulus of elasticity (6000-10000 MPa).The sample results of the modulus of elasticity taken from region 4, whose spacing is larger than those of others, are the highest and belongs to the group of "medium" degree trees.Modulus of elasticity and their classification for some tree species were shown in Table 10.
Table 10.Modulus of elasticity and its classes for some tree species.
Overall average modulus of elasticity in bending (9877 MPa); is higher than those of maple and alder, but lower than those of beech-bodied maple, eucalyptus, ash, white and common ash.

Impact Bending Strength
Descriptive statistics of impact bending strength are shown in Table 11.According to Duncan test results given in Table 11, in terms of impact bending strength; There is no statistically significant difference between regions 2 and 3, however, overall average impact bending strength was 91,8 J/m in region 1; 72,7 J/m in region 2; 64,9 J/m in region 3; and 133,1 J/m in region 4. Table 11.Values of impact bending strength (J/m).
According to the results obtained, impact bending strength was highest in region 4 with a value of 133,1 J/m; and lowest in region 3 with a value of 64,9 J/m.
Narrow-leaved ash belongs to group of trees with a "very high" degree with a impact bending strength value of 90,6 J/m.Of all the regions, the highest impact bending strength was found in region 4 with the highest value of 133 J/m.Impact bending strength of regions 4 and 1 belongs to group of trees with "very high" degrees.Impact bending strengths and their classes are given for some tree species in Table 12.
Table 12.Impact bending strengths and their classes for some tree species.
Narrow leaved ash belongs to group of trees with a "very high" degree with a impact bending strength value of 90,6 J/m.Based on this result; its impact bending strength is higher than those of sharp fruity ash, eastern beech, alder and common ash, but lower than those of common ash and beech.Oliver and Larson (1996) examines the anatomy, annual ring width, timber quality, physical and mechanical resistance properties of Fraxinus excelsior in wide spacing, states that it has more diameter increments in wide spacing.
Table 15.Tensile strength perpendicular to grain for some tree species.
In the experiments conducted, the overall average tensile strength perpendicular to grain of narrow-leaved ash was found as 5,27 MPa.Based on these results; its tensile strength perpendicular to grain is higher than those of sharp-fruited ash, but beech-bodied maple, common ash and oak.

CONCLUSIONS
We determined the effects of spacing on some mechanical properties of narrow-leaved ash (Fraxinus angustifolia) wood in accordance with the purposes.The major findings were as follows: It has been determined that wide spacing increases density in narrow-leaved ash, and also boost the resistance properties in a positive way.According to these results, materials with the best mechanical properties are obtained from region 4, having the widest spacing (Table 1).
The mechanical properties of narrow-leaved ash wood capable to give the highest value in region 4, with the highest spacing; the increased diameter and number of knots together with the formation of the tapered body depending on the widened spacing, and also the reduced resistance quality value represent an obstacle to suggest the region 4, with the widest spacing, as the plantation spacing.
The spacing type in region 1 (2x3 m), which is in the highest quality group according to timber quality classes and allows formation of the cylindrical body, is considered to be more suitable for narrow-leaved ash plantations and is recommended.It has been instrumental in the creation of this opinion that the resistance and quality values of the wood samples taken from region 1 are close to the average value of four plantations.

Figure 1 .
Figure 1.(a) Compression strength parallel to grain, (b) bending strength and (c) impact bending strength testing.

Figure 2 .
Figure 2. Compression strength static quality values for Fraxinus angustifolia.

Figure 3 .
Figure 3. Values of bending quality and results for Fraxinus angustifolia.