**4. Discussion**

The results of the current study revealed that the size of the wounds for resin collection from red pines could be temporally divided into the Japanese colonial period and post Korean War period. Especially, from the end of the 1930s to the middle of the 1940s, resin collection was very intensive in the Republic of Korea to support the fuel for Japanese weapons [7]. To effectively collect a huge amount of resin, the panel hacksaw method was applied, which makes larger wounds (Figure 7A) than the traditional chisel method in Korea (Figure 7B). This information can be mainly verified from historical documents.

**Figure 7.** Wounds by (**A**) panel hacksaw method and (**B**) conventional chisel method.

The panel hacksaw method was mainly used between 1938 and 1945. Only BM in G1 (Table 2) showed such hacksaw wounds dated between 1944 and 1952 (Table 5). BM is located in a small island which is not well accessible from the inland. Due to BM's geographical location, the panel hacksaw method has been applied there later than other sites [2]. Unlike the G1 sites, one site in G2 (Table 2), viz. HI1, was dated between 1940 and 1944 for the resin collection. Haeinsa is one of the three Jewel Temples in the Republic of Korea, which was listed as a UNESCO World Heritage Site in 1995. Therefore, from a religious standpoint, the panel hacksaw method which makes large wounds might have not been used in Haeinsa.

The annual rings in the red pines comprised earlywood formed between spring and summer, and latewood formed between summer and autumn, similar to the conifer tree species in the northern hemisphere [26,27]. Therefore, the early- or latewood in the outermost annual ring can give seasonal

information on resin collection. However, when the resin collection is determined, the wood cell development process needs to be considered. The development of the wood cells passes through the following processes: cell division in the cambium, cell expansion or elongation, cell wall thickening, cell wall sculpturing, lignification [29]. When wounds are made, the mature wood cells remain intact but the cambial cells, and the cells involved in cell expansion/elongation, cell wall thickening, and lignification, can be easily removed. These cells can be easily destroyed even by a small physical force [30]. Therefore, in most cases, the cells which are physically stable can be observed at the outermost tree ring on the wound surface. Due to this reason, the resin collection seasons can be determined one season earlier.

Most records and research on resin collection focus on the wound size and/or the technique and/or years of resin collection [2,31]. Although the diameters of red pines at the resin collection years can provide information about the forest conditions related to the trees at that time, it has not been well investigated. In the present study, the smallest and largest diameters of the red pines at each site varied from 20.5 (HI3) to 25.8 (BM and NW) cm and from 26.9 (NS) to 45.1 (NW) cm, respectively. These results indicated that the red pines thicker than 20.0 cm were used for resin collection, while trees thicker than 45.0 cm were rare.

Trees have an ability to heal wounds by forming callus tissue around the edges of the wound [32]. The duration to completely cover a wound is strongly related to the size of the wound. The current study found that some wounds created by the conventional chisel method could successfully seal the wounds (Figure 7B); however, the wounds caused by the panel hacksaw method required a long time (Figure 7A). When natural resources are obtained from trees through wounding, the wound size is considered based on the sealing ability of trees.

The panel hacksaw method is useful in increasing the collected amount of pine resin in the short term. However, it left irrevocable wounds which still exist in Korea. Unlike the panel hacksaw method, the conventional chisel method cannot produce a huge amount resin within a short period; however, it offers the advantage of sustainable collection of resin. Sustainable use of non-timber products has countless value and should be transferred to the next generation to maintain a safe and happy life.
