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1. INTRODUCTION
Tree growth is determined by the tree's own genetic and environmental factors, and tree rings are formed every year through continuous increase in the thickness and height of trees (Teskey et al., 1987). Among the elements of the tree ring, the tree-ring width is easy to measure and stores various environmental information; therefore, it is commonly used in tree-ring dating (Seo et al., 2017). Tree-ring dating is a method used to measure the age of trees using the width of the tree rings, and to use this method, it is necessary to establish a standard tree-ring chronology for each region and species (Lee et al., 2018). Pine, a major tree species in Korea's forests, was the most preferred building material in Korea (Park and Lee, 2007), and since the establishment of a standard tree-ring pattern for pine trees at the end of the Goryeo period, tree-ring dating of many wooden structures are being conducted (Lee et al., 2021).
Tree-ring dating has been used for the domestic wooden structures in many buildings, first of which was the Gyeonghoeru Pavilion in Gyeongbokgung Palace. Among them, a study confirmed the mutual relationship between the 55 wooden elements of Daeungjeon in the Yeongguk Temple in Yeongdong and the carbonized building elements excavated from the lower part of Daeungjeon using absolute dating (Son et al., 2006). Another study conducted species identification and tree-ring dating of the wooden elements in Daeseongjeon of Jipyeonghyangyo in Yangpyeong and identified 43 hard pine and 6 soft pine trees and confirmed their felling dates to be 1718 and 1720, which enabled the confirmation of the repair period by comparing them with the historical records (Son et al., 2011). Additionally, by tree-ring dating of the wooden elements and heartwood materials of the main, wing, and entrance parts of the Gwanghanru Pavilion in Namwon, the felling dates of the wooden elements of the primary and wing parts were discovered to be similar, which enabled the comparison and confirmation of the period of construction, renovation, and extension of the entrance part with historical records (Park et al., 2014). Species identification and tree-ring dating was performed for the wooden elements of Daeunjeon of the Hwagyesa Temple in Seoul, and the presence of 26 hard pines and 1 tree of the Abies spp. were confirmed. After performing tree-ring dating, the felling dates of the wooden elements were found to be 1869 and 1870, which were confirmed to be consistent with those in the construction and hidden material records (Bokjangmul) in Jongdori (Lee et al., 2020). Since such wooden buildings are made of biological materials, they are vulnerable to decay and deterioration, and with time, they will be exposed to damage by wind and insects (Eom and Park, 2018). Therefore, to maintain a wooden structure for a long time, repairs and replacements of elements are carried out. Accordingly, it is important to understand the construction, repair, and replacement periods of the structures.
Mungyeong Juheulgwan of Joryeong (Gate No.1) is the historic site no. 147, and the fortress has a gatehouse with a 3-block wide and 2-block long hipped and gabled roof and two side doors (Fig. 1). Among the three gates of Mungyeong Saejae, the first gate (Juhulgwan) has the oldest appearance and is said to have been built in 1709 (35th year of King Sukjong). It was recorded in “Juheulgwan Jungsugi” that after its construction, repairs were carried out in 1752 (28th year of King Yeongjo), 1772 (48th year of King Yeongjo), and 1840 (6th year of King Hyeonjong); additionally, it was engraved on Juheulgwan Walls that it was reconstructed and extended in 1721 (1st year of King Gyeongjong), 1748 (24th year of King Yeongjo), 1808 (8th year of King Sunjo), 1880 (17th year of King Gojong), and 1886 (23rd year of King Gojong) (Mungyeong city, 2020). However, these records only recorded the time of reconstruction and repair of Juheulgwan, and it was impossible to confirm the type of wood used, their date of felling, date of use, etc.
Therefore, in this study, tree-ring dating was performed for the wooden elements in the gatehouse and side doors of Mungyeong Juheulgwan of Joryeong (Gate No.1) to determine the time of reconstruction and repair. In addition, species identification was conducted for the same wooden materials to validate the tree species used.
2. MATERIALS and METHODS
Core samples from the area close to the tree skin were obtained from 84 wooden elements (containing ≥50 tree rings) of the gatehouse and side doors of Juheulgwan (Tables 1 and 2). The samples were obtained via a coring method in which a specially prepared core-type bit was combined with an electric drill to obtain a core (within a diameter of 6 mm and a length of 8 cm). After obtaining the sample, the punctured part was treated using an antiseptic (Wood keeper-A, Hanchem, Korea) and was filled with resin for the maintenance of the cultural properties of the wooden materials (Resin-SV 427, hardener-HV 427). The coring method has been applied to several buildings since the early 2000s. It never leads to problems such as deterioration or deformation of the wooden elements because it uses resin for the maintenance of the cultural properties of the elements, which can be restored after sample collection.
| Sample | Number | Sample | Number | ||
|---|---|---|---|---|---|
| Pillar | Gidung | 3 | Purlin | Dori | 2 |
From the cores obtained for tree-ring dating, three-section slices with a thickness of approximately 20 μm were prepared by hand sectioning using a razor blade. The three sections were placed on a glass slide, 50% of aqueous glycerin solution was added, and a preparat for species identification was prepared while taking care that bubbles are not formed. An optical microscope (Eclipse LV100, Nikon, Japan) was used to observe the tissues in the prepared sections, and pictures were taken of the features that were found to enable identification of the tree species.
The collected cores were attached to a fixed stand and sanded using sandpaper such that the tree rings could be clearly observed. The tree rings of each sample were measured with an accuracy of 0.01 mm using a stereomicroscope (LEICA-S4E, Leica, Germany) and a tree-ring width measurement equipment (LINTAB Germany) connected to the TSAP-Win software (Rinntech, Germany). Cross-dating was conducted to identify the false and true rings of the measured samples and assign the exact age to each tree ring (Kim and Park, 2005; Speer, 2010; Soltani et al., 2021). The representative cross-dating methods utilized in tree-ring dating involve a statistical method that calculates the mutual conformity in the tree-ring dates and a graphic method in which the conformity in tree-ring chronology is visually confirmed (Schweingruber, 1988; Norrgard and Helama, 2021). The statistical method can be considered significant at the 1% level when the t-value is ≥3.5, and the Gleichläufigkeit (glk) value is ≥65% or more when the tree-ring width graphs for ≥100 years are compared (Park et al., 2003). Therefore, for tree-ring dating, both graphical and statistical analyses were conducted. To assign an absolute year to the written Mungyeong Joryeong Juheulgwan chronology, cross-dating was conducted using the standard chronology of hard pine owned by the Korea National University of Cultural Heritage.
3. RESULTS and DISCUSSION
The species identification results of the 84 wooden elements (79 from the gatehouse and 5 from the side doors of Mungyeong Juheulgwan of Joryeong) showed that 76 of them were hard pines, 5 were soft pines, and 3 were Abbies spp. Tables 3 and 4 summarize the species identification results according to the type of wooden element.
| Sample | Species | Sample | Species | ||
|---|---|---|---|---|---|
| Pillar | Gidung 1 | Soft pine | Purlin | Dori 1 | Hard pine |
| Gidung 2 | Hard pine | Dori 2 | Hard pine | ||
| Gidung 3 | Soft pine | Total | 5 | ||
This softwood undergoes a rapid transition from earlywood to latewood. Vertical vessels with thin-walled epithelial cells were observed under optical microscope. The ray cells were composed of ray parenchyma and ray tracheid, and one window-like pit was observed in the cross-field. Particularly, dentate thickening, which is the main feature of hard pines belonging to the Pinus spp., was observed in the ray tracheid. In the longitudinal ray tracheid, an arrangement of bordered pits was observed in one row. In the tangential section, horizontal vessels were observed, and uniseriate and fusiform ray cells were also observed (Fig. 2). Within the Pinus spp., hard pines and soft pines exist, and the sample was finally identified as hard pine since dentate thickening was observed.
This is a hardwood that undergoes a slow or slightly rapid transition from earlywood to latewood. When viewed under optical microscope, vertical vessels with thin-walled epithelial cells were observed. The ray cells consisted of ray parenchyma and ray tracheid, and two window-like pits of one were mainly seen in the observation field. Unlike the hard pines that belong to the Pinus spp., dentate thickening was not observed in the ray tracheid. A one-row arrangement of bordered pits was observed in the longitudinal ray tracheid. In the tangential section, horizontal vessels were observed. Additionally, both uniseriate and fusiform ray cells were observed (Fig. 3). The Pinus spp. consist of both hard and soft pines; however, since dentate thickening was not observed, the sample was finally identified to be soft pine.
This is a softwood that undergoes a gradual transition of tracheids from earlywood to latewood. No normal resin canals were observed in the prepared cross-section. The ray cells comprised only of ray parenchyma, and the horizontal wall of the ray parenchyma had well-developed simple pit pairs and modular end walls. In the cross-field, 2–3 taxodioid pits were observed. The bordered pits in the longitudinal ray tracheid were arranged in one or two rows. No horizontal vessels were observed in the tangential section, and only uniseriate rays were observed (Fig. 4). The Abies spp. distributed in Korea consists of three species, namely, A. holophylla, A. nephrolepis, and A. koreana; however, since they are anatomically indistinguishable, the sample was finally identified as Abies spp.
Among the 84 samples obtained from the gatehouse and side doors of Mungyeong Juheulgwan of Joryeong, 76 samples of hard pine, excluding the 5 samples identified as soft pine and 3 samples identified as Abies spp., were included for further analysis. Among the 76 samples, 54 were similar to each other, creating Chronology 1 (Joryeong 1S; Fig. 5). The tree-ring period was 157 years, and to find out the exact year, cross-dating was conducted using the standard chronology of hard pine owned by the Korea National University of Cultural Heritage. On analysis, the t-value was found to be 6.7, and the G-value was 67%, which was a relatively high statistical value and graphically consistent (Fig. 6). Therefore, Mungyeong Juheulgwan of Joryeong (Gate No.1) hard pine Chronology 1 (Mungyeong 1S) was dated as 1744–1869. Among the wooden elements included in the chronicle, it was validated that wood harvested from the summer of 1792 to the early spring of 1794 was used for some pillars, groves, and sangyeons with bark, and most of the elements were made from wood harvested from the late autumn of 1838 to the early spring of 1840. Additionally, it was confirmed that the timber for the unknown floor element 1 and the unknown roof element 3 were felled between the early spring and autumn of 1867 and 1872, respectively. Furthermore, the floor joists and five joists were similar to each other, thereby creating Chronology 2 (Joryeong 2S). The tree-ring period was found to be 113 years, and on performing cross-dating using the hard pine standard chronology, the statistical values of t-value (4.7) and G-value (61%) were found to be graphically consistent. Therefore, Mungyeong Joryeong Gwanmun Gate 1 (Juheulgwan) hard pine Chronology 2 (Joryeong 2S) was dated as 1596–1709 (Fig. 7). Two of the elements involved in the chronicle (floor joists 2 and joists 2) had bark; therefore, it was confirmed that they were felled between the summer of 1708 and late autumn of 1709.
On conducting species identification of the 84 wooden elements of Mungyeong Juheulgwan of Joryeong (Gate No.1), 76, 5, and 3 wooden elements were identified to be hard pine, soft pine, and Abies spp., respectively. Pine trees of the hard pine type are species that grow wild in all regions of Korea, except for the northern highlands of the Korean Peninsula, and were found to be mainly used in wooden structures in the Joseon Dynasty as per previous studies (Park and Lee, 2007). The same results were validated in this study. There are three types of soft pines native to Korea―Korean pine, Ulleungdo white pine, and Dwarf stone pine. The Ulleungdo white pine is native to Ulleungdo, and the Dwarf stone pine is native to the northern part of the Korean Peninsula in which Seoraksan Mountain is the timberline; therefore, it is unlikely that the Ulleungdo white and Dwarf stone pines were used and highly likely that the Korean pine was used (Kong, 2000). Additionally, although A. holophylla, A. nephrolepis, and A. koreana belong to the Abies spp., A. nephrolepis and A. koreana are mainly distributed in highland areas; therefore, it is believed that A. holophylla was used (Lee, 1997). Furthermore, soft pine and Abies spp. are unsuitable for use as building materials because they are less sturdy than hard pine. Therefore, it was considered that Mungyeong Joryeong Juheulgwan was built mainly using hard pine; however, if the supply of hard pine was insufficient, soft pine and Abies spp. were used. This is consistent with the results that stated that hard pine was primarily used in the palace and administrative buildings during the Joseon Dynasty, but some soft pine and Abies spp. were also used (Park and Lee, 2007).
Because of tree-ring dating, dates were assigned to 59 of the 76 hard pines analyzed, and 4 felling dates were identified. It was confirmed that the joist members of the floor were felled between the summer of 1708 and late autumn of 1709, and thus were considered to be early construction members. Most of the other members were felled throughout one and a half years, from late autumn of 1838 to early spring of 1840, and it is believed that large-scale repairs were carried out 130 years after the construction. Additionally, it is believed that some of the outer columns, nurigae, and sangyeon were felled between the summer of 1792 and the early spring of 1794, showing that repairs and replacements of some members were carried out 150 years after the large-scale repair. Afterward, it was confirmed that a floor member, presumed to be a dongbari, and one unidentified roof member each were felled in 1867 and 1872, suggesting that after 1872, a simple repair was carried out on the floor to replace some decomposed parts with dongbari, in addition to carrying out repairs on the roof (Fig. 8).
: Side door material).
4. CONCLUSION
Mungyeong Joryeong Juheulgwan selectively used hard pine as building materials for the gatehouse and side doors. It was confirmed that soft pine and Abies spp. were used for some missing members; this result was consistent with that of a previous report on the tree species used in the palace and official buildings of the Joseon Dynasty (Part et al., 2018). Additionally, the chronology prepared by tree-ring dating correlated the highest statistical value with the Chungcheong-do standard chronology of hard pine from Worak Mountain and Songni Mountain, suggesting that the hard pine that was naturally grown near Mungyeong was supplied for use in repairs and replacements.
The tree-ring dating identified 4 felling dates for the 58 wooden elements of the gatehouse and 1 wooden element of the side door. The confirmed felling dates were compared with the construction and repair records of Joryeong Juheulgwan in Mungyeong (Annals of Joseon Dynasty, Juheulgwan Jungsugi, and engravements on Juheulgwan Walls; Table 5). Among the records of Joryeong Juheulgwan in Mungyeong, “Annals of Joseon Dynasty-Sukjong” and “Yeojidoseo” contained the records where the construction of Joryeong was discussed in the 34th year of Sukjong (1708), and it was stated that construction started from the spring of the following year, the 35th year of Sukjong (1709) (Mungyeong city, 2020). Many joists, which were floor members, were confirmed to have similar dates through tree-ring dating, suggesting that they were the early construction members. In “Juheulgwan Jungsugi,” there is a record that state that repairs were carried out in the 6th year of King Heonjong (1840), and as most of the members were confirmed to be felled between 1838 and 1840, it was judged that reconstruction or large-scale repairs were carried out in 1840 (Mungyeong city, 2020). Additionally, there was a record engraved in the Juheulgwan Walls that stated that repairs were carried out in 1808. Using tree-ring dating, it was confirmed that columns and dori were felled between 1792 and 1794, suggesting that relatively heavy repairs were carried out in 1808 using the timber they felled 10 years ago. Furthermore, according to the records on the fortress walls that stated that repairs carried out in 1880 and 1886, it was believed that were used for simple repairs to the floor and roof using woods, which were felled in 1867 and 1872, respectively.
Different repair records of Mungyeong Joryeong Juheulgwan were confirmed through the books and engravings on the fortress walls. These were consistent with the results of tree-ring dating obtained in our study, which once again confirmed the accuracy of tree-ring dating. Additionally, because there was a difference of approximately 10 years between the repair records and felling dates of some elements of the building, it was assumed that the timber was felled and stored at that time. We believe that it will be possible to gain more precise information regarding the storage methods and usage of the wood used in buildings during the Joseon Dynasty once tree-ring dating is continuously conducted for other Joseon Dynasty buildings as well.
