1. INTRODUCTION
Korean red pine trees have excellent quality (physical and mechanical properties) and are representative species of Korea that have been used in palaces, temples, houses, furniture, ships and so on. As the most favorite tree of our people, it has been revealed that 71% of architectures in Goryo era, 73% of architectures in mid-Joseon era, and 88% of architectures in late-Joseon era were constructed using them (Park et al., 2007).
As the properties of pine trees vary depending on the production region (Han et al., 2015), for more efficient use of pine trees and the superior breeding of them, it would be necessary to investigate the reasons for the different properties depending on the production region. The investigation of differences in properties will first be on anatomical, physical and mechanical ones.
In this study, we selected three regions, Yeongdong (Goseong-gun), Yeongseo (Hongcheon-gun) and Yeongnam (Bonghwa-gun), representative pine tree production regions in Korea to get samples, and an anatomical research was conducted to determine differences between the length and the diameter of the tracheid. And it was revealed that there were differences in the length and the diameter of the trachied (Kim et al., 2018).
Therefore, in this study, the purpose of this study was to investigate the difference of physical properties following the study of the anatomical characteristics (Kim et al., 2018) of the Korean pine in the previous paper by regional groups, and the physical properties of lumber are basically attributable to their anatomical properties so that their anatomical properties are also reviewed.
2. MATERIALS and METHODS
For this study, we received a pine tree from Yeongdong (Goseong-gun), Yeongseo (Hongcheon-gun) and Yeongnam (Bonghwa-gun), respectively in 2015. They were originally possessed by the East Sea Timber Distribution Center of Forest union. The thickness of the discs were about 20 cm and the no. of tree rings, chest diameter, mean ring width, and latewood proportion at the time of receipt are shown in Table 1 (Kim et al., 2018) and sampling is shown in Fig. 1 (Park et al., 2015). In addition, for the comparison of the same year and area, the year of harvesting was estimated using the annual-ring method, which was analyzed as 2014 for Goseong, 2012 for Hongcheon, 2014 for Bonghwa (Kim et al., 2018).
| Province* | No. of Tree rings | Diameter (cm) | Average of ring widths (mm) | Latewood proportion (%) |
|---|---|---|---|---|
| Goseong-gun (G) | 85 | 48 | 3.1 | 22.87 |
| Hongcheon-gun(H) | 82 | 42 | 2.6 | 20.19 |
| Bonghwa-gun (B) | 76 | 46 | 3.1 | 18.57 |
The water content of trees of each production site was measured as green moisture content (artificial) and air-dry moisture content. For the measurement of green moisture content, as about 1~3 years has passed after harvesting, samples were immersed in distilled water until there was no difference in weight. The size of the specimens from each tree production region was 2 cm (T) × 2 cm (R) × 2 cm (L) in size and 5 ~ 8 pieces of heartwood and 4 ~ 6 pieces of sapwoodspecimens were taken, respectively (Fig. 1). The preparation and measurement of the specimen was in accordance with KS F 2199 (2001).
The specific gravity of each tree production region was measured based on green, air-dry, and oven-dry specific gravity. The size of the specimen was 2 cm (T) × 2 cm (R) × 2 cm (L) square. At this time, they were classified as heartwood (5 ~ 8) and sapwood (4 ~ 6) (Fig. 1). The preparation and measurement of the specimen was in accordance with KS F 2198 (2001).
The shrinkage of each tree production region was measured based on air-dry shrinkage and total shrinkage. The specimen was produced consecutively from the number of the square with dimensions of 2 cm (T) × 2 cm (R) × 2 cm (L) (11~14 units). In order to measure the length of the specimen, a line in the radial and tangential directions was drawn on the cross section using a vernier caliper (Fig. 1). The specimen preparation and measurement methods are in accordance with KS F 2203 (2004).
In order to measure the hygroscopicity of each tree production region, 4~6 specimens were prepared with the size of 3 cm (T) × 3 cm (R) × 0.5 cm (L) and taken consecutively from trees. At the time of preparation, the two sides were straight grained rectangular parallelepiped with the short axis parallel to the direction of the fiber (Fig. 1). The samples were humidified in a constant temperature and humidity (LHT-2250C, LabTech,Korea) to the temperature of 40°C, relative humidity of 75%/40°C, and relative humidity of 90%, until there was no weight change. The specimen preparation and measurement method is in accordance with KS F 2205 (2004).
3. RESULTS and DISCUSSION
Table 2 shows the air-dry moisture content and green moisture content of pine trees in Goseong-gun, Hongcheon-gun, and Bonghwa-gun. The air-dry moisture content in the heartwood part was 13.7% in Goseong-gun pine, Hongcheon-gun pine 12.4%, and Bonghwa-gun pine 13.9%. For sapwood part, Goseonggun pine 14.0%, Hongcheon-gun pine 12.5%, and Bonghwa-gun pine 13.8%, respectively. The green moisture content was 71.4% for Goseong-gun pine, 76.9% for Hongcheon-gun pine, 90.9% for Bonghwagun pine for heartwood part, and 166.7% for Goseonggun pine, 134.4% for Hongcheon-gun pine, and 110.3% for Bonghwa-gun pine for sapwood part.
In the Duncan test for differences between the tree production regions, the air-dry moisture content was 12.5% for Hongcheon-gun pine, which is smaller than 14.0% for Goseong-gun pine and 13.8% for Bonghwagun pine in sapwood. And it was revealed that there are no difference in the regions in terms of air-dry moisture content of heartwood and green moisture content of heartwood and those of sapwood.
The green moisture content revealed by study conducted by Jo et al. (1982) was 84%for Korean nut pine, 94% for pine tree, 91% for Japanese black pine tree, and 91% for red pine tree, regardless of whether it is heartwood or sapwood. These values are similar to the artificial green moisture content of the heartwood part used in this study. Kang et al. (2008) reported that the green moisture content varies widely depending on the species of trees,but the green moisture content of most species is 30-200%. In Korea, the average air-drymoisture content is reported to be 14.2% in the case of moisture-proof and 13.2% in the case of moisture absorption. Kim et al. (2008) found that air-dry moisture content was 12.7% for sapwood of pine wood in Jeonbuk Muju area, 10.3% for sapwood. And 10.9% for heartwood and 10.7% for sapwood in Anmyeongdo pine trees. Compared to this study, the pine trees of Goseong, Hongcheon, and Bonghwa-gun showed higher air-dry moisture content than those of Muju and Anmyeongdo pines.
Table 3 shows the oven-dry, air-dry and green specific gravity of Goseong-gun, Hongcheon-gun and Bonghwagun. For the oven-dry specific gravity, Goseong-gun pine was 0.45, Hongcheon-gun pine 0.40, Bonghwa-gun pine 0.46 for heartwood part, and Goseong-gun pine was 0.37, Hongcheon-gun pine 0.41 and Bonghwa-gun pine 0.45. for sapwood part. Statistically, Goseong-gun and Bonghwa-gun pine trees showed that they are high in the heartwood part and Hongcheon-gun pine tree was low. Bonghwa-gun pine showed highest, followed by Hongcheon-gun pines, and Goseong-gun pines for sapwood part. For the air-dry specific gravity, Goseonggun pine was 0.47, Hongcheon-gun pine 0.42, Bonghwagun pine 0.49, respectively. For sapwood part, Goseonggun pine was 0.40, Hongcheon-gun pine 0.44 and Bonghwa-gun pine 0.48, respectively. Statistically, in the heartwood part, Goseong-gun and Bonghwa-gun pine trees showed high as same with oven-dry specific gravity and Bonghwa-gun pine tree showed high in sapwood part. For the green specific gravity, Goseonggun pine was 0.48, Hongcheon-gun pine 0.44, Bonghwagun pine 0.54, for heartwood part. For sapwood part, Goseong-gun pine was 0.42, Hongcheon-gun pine 0.46, Bonghwa-gun pine 0.51, respectively. Statistically, Bonghwa-gun pine was the highest in the heartwood part, while Goseong-gun and Hongcheon-gun pine showed no difference. Bonghwa-gun pine was the highest in sapwood, followed by Hongcheon-gun and Goseong-gun pine. Overall, the Bonghwa-gun pine trees were higher than the two other tree production regions in the heartwood section, and the gap was prominent for the sapwood part. Goseong-gun pine trees were higher in the heartwood part while Hongcheon-gun were higher in sapwood part. However, the specific gravity of the Goseong-gun pine tree which showed high in heartwood part can be higher. Therefore, Goseong-gun pine tree with high specific gravity of heartwood part can be expected to be stronger than Hongcheon-gun pine tree as a whole. Kim et al. (2008) reported that the air-dry specific gravity (heartwood, sapwood) and green specific gravity (heartwood, sapwood) of pine trees in Muju, Jeonbuk Province were 0.49, 0.43 and 0.40, 0.40, and 0.44, 0.45 and 0.40, 0.40 for Anmyeondo pine tree, and 0.45, 0.45, and 0.51, 0.45 for Chunyang pine, respectively. The air-dry specific gravity of the pine tree was reported to be 0.47, and the oven-dry specific gravity 0.44 in the study of Jung et al. (2008) on Korean useful wood. In addition, Cho (1994) reported that green specific gravity of pine trees is 0.70 and air-dry specific gravity 0.47. Green specific gravity is considered the green weight, therefore the green specific gravity (oven-dry mass) in this study will be difficult to compare with. These reports showed values similar to those of Goseong and Hongcheon area.
Table 4 shows air-dry shrinkage, total shrinkage and T/R ratio of pine trees in Goseong-gun, Hongcheon-gun and Bonghwa-gun. In the tangential direction of air-dry shrinkage, Goseong-gun pine was 2.86%, Hongcheongun pine 3.94% and Bonghwa pine 4.39%. In radial direction, Goseong-gun pine was 1.73%, Hongcheongun pine 2.09% and Bonghwa-gun pine 2.29%, respectively. The T/R ratio was measured to be 1.67% for Goseong-gun pine, 1.89% for Hongcheon-gun pine, and 1.92% for Bonghwa-gun pine. For the tangential direction of the total shrinkage, Goseong-gun pine was 6.32%, Hongcheon-gun pine 6.58% and Bonghwa-gun pine 9.85%, respectively. And for the radial direction, Goseong-gun pine was 2.83%, Hongcheon-gun pine 3.44%, and Bonghwa-gun pine 3.68%. The T/R ratio was 2.11% for Goseong-gun pine, 1.04% for Hongcheon-gun pine, and 2.68% for Bonghwa-gun pine tree. The result of the Duncan test to determine differences between the tree production regions revealed that Hongcheon-gun pine and Bonghwa-gun pine trees showed high tangential air-dry shrinkage. Bonghwa-gun pine trees were high in the total shrinkages while there was no difference between the tree production regions for radial direction.
Fig. 2 shows the relationship between tracheid length (Kim et al., 2018) and shrinkage in three tree production regions. In the figure, shrinkage and tracheid length were found to be proportional. Kim et al. (1998), Hiller (1964), Mark (1967), Preston (1952), Wellwood (1962), and Wadanabe et al. (1964) reported that the tracheid length was negatively correlated with the microfibril angle. In other words, the longer the tracheid length, the smaller the microfibril angle and the shorter the tracheid length, the larger the microfibril angle. Barber et al. (1964) reported that shrinkage in fiber direction increased with increasing micro fibril angle, while lateral shrinkage decreased with decreasing microfibril angle. In this study, it is thought that the larger shrinkage in the lateral shrinkage in Bonghwa-gun pine trees is due to the longer tracheid length. In order to prove this further, the investigation of these microfibril angles would be necessary in the future.
Kim et al. (2008)'s study revealed that the T/R ratio of Anmyeondo pine is 2.91. The T / R ratio of Anmyeondo pine was higher than those of Goseonggun, Hongcheon-gun and Bonghwa-gun when compared with this study. In the study of Cho (1994), the pine shrinkage was 4.88% in the radial direction, 9.11% in the tangential direction, and 0.31% in the fiber direction in the total shrinkage. The shrinkage in radial direction was higher than the three regions and the tangential was higher than those of Goseong-gun and Hongcheongun and lower than Bonghwa-gun pine trees. The air-dry shrinkage was 2.97% in the radial direction, 5.40% in the tangential direction, and 0.16% in the fiber direction, showing higher values than those from three regions.
Table 5 shows the hygroscopicity of pine trees in three areas: Goseong-gun, Hongcheon-gun and Bonghwagun. For hygroscopicity for each region at 40 °C and 75% relative humidity, 13.0% for Goseong-gun pine, 13.0% for Hongcheon-gun pine, and 13.3% for Bonghwa-gun pine, respectively. And hygroscopicity at 40 °C and 90% relative humidity showed little difference between tree production regions, with 16.9% for Goseong-gun pine, 16.7% for Hongcheon-gun pine, and 16.9% for Bonghwa-gun pine, respectively. Haishi et al. (1973) studied the equilibrium moisture content of major Japanese species ranging from 9.7 to 13.7% at a relative humidity of 75% and a temperature of 40 °C, with an average of 12.3% for heartwood and an average 12.4 for sapwood, and 14.4 ~ 19.2% at 90% relative humidity, 17.4% for heartwood and 17.8% for sapwood. Domestic pine trees were higher in average hygroscopicity than major species of trees in Japan. Park et al. (2016) reported that the hygroscopicity of the introduced rubra-oak tree as per the tree production 11.5% on average at 40 °C and 90% relative humidity. Kim et al. (2017) reported no differences between hygroscopicity of domestic cork trees in indoor and outdoor environments. It was 12.2% on average at the 40 °C and relative humidity of 75% and 16.1% on average at the 40 °C and relative humidity of 90%.
| Province | Goseong-gun | Hongcheon-gun | Bonghwa-gun |
|---|---|---|---|
| Condition | |||
|
|
|||
| 40°C, 75%RH (%) | 13.0 ±0.2 B* | 13.0 ±0.3 B | 13.3 ±0.1 A |
| 40°C, 90%RH (%) | 16.9 ±0.4 a | 16.7 ±0.3 a | 16.9 ±0.4 a |
In the future, it will be necessary to investigate the hygroscopicity of major domestic species and to increase the number of samples for the study of regional anatomical and physical properties. These studies are expected to facilitate the efficient use of pine trees and breeding of species to be used as good materials.
4. CONCLUSION
In this study, moisture content, specific gravity, shrinkage and moisture absorption properties of pine trees in Goseong-gun, Hongcheon-gun and Bonghwagun were investigated. Air-dry moisture content and green moisture content are the same regardless of the tree production regions. Specific gravity of the heartwood part and the sapwood part of Bonghwa-gun pines was higher than that of the other two tree production regions. Goseong-gun pines in the heartwood part and Hongcheon-gun pines in the sapwood part were higher than the other when Goseong-gun and Hongcheon-gun pine trees were compared. Goseong-gun pine tree with higher specific gravity of heartwood part can be judged to be stronger than Hongcheon-gun pine tree as a whole. There was no difference in shrinkage regardless of the radial directions among the tree production regions. For the tangential direction, Bonghwa-gun pine and Hongcheongun pine trees were high in air-dry shrinkage, and Bonghwa-gun pine trees were high in total shrinkage, which was consistent with the order of the tracheid length. Hygroscopicity showed little difference between the tree production regions. We hope that based on the findings from this study, we can use pine efficiently and they will help to produce good varieties.
