The objective of the present study was to develop a dendrochronological method for accurately estimating the age of big old trees with high cultural, historical, and public interest values, as well as examining the applicability of resistograph.
Study regions consisted of Chungcheongbuk-do Goesan-gun (CBGS), Jeollanam-do Gurye-gun (JNGR), and Gyeongsangbuk-do Uljin-gun (GBUJ), which have numerous protected trees registered, and the experimental tree species were of Zelkova serrata and Pinus densiflora therein. The number of Zelkova serrata collected from CBGS, JNGR, and GBUJ was 12, 8, and 6, respectively, and the number of Pinus densiflora was 10, 3, and 9, respectively. An increment borer was used for sampling in all experimental sites and in CBGS, a resistograph was also used for sampling.
It is important to obtain an increment core in the direction to the pith when we estimate the tree age. For trees with upright trunk, increment cores have to be extracted in the direction to the center of the stem at the height as close as possible to the ground. If the stem has rotted close to the ground, the cores should be collected from the upper part of the trunk or branches. If the tree is growing on a slope or is tilted, the cores should be collected from a location above or below the tilt. For trees such as those of the Zelkova serrata that branch in all directions, the cores should be collected from the area below the branch with the largest diameter.
For definitive observations of tree-ring boundary in the increment cores, the cross section of the samples was cut or sanded using a sliding microtome for the Zelkova serrata and sandpaper for Pinus densiflora. Thereafter, the ring widths were accurately measured in the resolution of 0.01 mm, and the cross-dating method used in dendrochronology was employed to accurately date all tree rings in increment cores. Only increment cores successfully cross-dated were used to establish the local mater chronologies for the Zelkova serrata and Pinus densiflora representing the study regions. The length of the local mater chronologies from the CBGS, JNGR, and GBUJ were 203 (1813?2015), 201 (1815?2015), and 203 (1813?2015) years for the Zelkova serrata and 154 (1862?2015), 175 (1841?2015), and 250 (1766?2015) years for the Pinus densiflora, respectively. By the local master chronologies, which are the reference to find false rings, narrow rings, and missing rings, the accuracy in the estimation of tree age could be remarkably improved. In the comparisons between local mater chronologies, Zelkova serrata local master chronologies t-values of 0.7?1.0 and Gleichlaeufigkeit (Glk) values of 59.2?64%, indicating a statistically low agreement. On the other hand, Pinus densiflora showed t-values of 0.6?12.0 and Glk values of 58.5?66.7%, which were higher than those of the Zelkova serrata, but still showed a statistically low agreement, excepting between CBGS and JNGR. In the comparisons of the average temperature and precipitation for the last 50 years with the local master chronologies, the chronological patterns were affected more by precipitation than by temperature. Therefore, to accurately date tree rings collected from various regions for tree age estimation, it will be very necessary to construct an additional local master chronologies considering of precipitation.
A resistograph was used for the first time in Korea to estimate the age of big old trees while minimizing any damage to the tree stem. Before age estimation of big old trees, a preliminary survey was conducted on Larch, Douglas fir, Korean pine, Fir, and Zelkova trees, and the suitable speed to insert the measurement needle into the stem were 100, 100, 175, 150, and 50 cm/min, respectively. The rotational speed was set to 1500 rpm, regardless of the tree species. Using this as the basis, tree age estimation was performed on three Zelkova serrata and seven Pinus densiflora from CBGS. For big old trees, the insertion speed was different from that used for the preliminary survey with 50 and 150 cm/min for the Zelkova serrata and Pinus densiflora, respectively. Therefore, for on-site application of resistograph, it is necessary to verify the suitable amplitude for the conditions of each tree species. Resistographic tree age estimation was made possible by comparing the annual ring-width chronology, which does not include narrow rings in the heartwood, with the representative local master chronology.
To adjust for height growth period up to the height where the core samples were collected for age estimation, a survey was conducted on 1 and 2-year-old Zelkova serrata (21 and 10 trees, respectively) and 7-year-old Pinus densiflora (30 trees) growing at open area (Jeonjang-ri, Oesan-myeon, Buyeo-gun, and Chungcheongnam-do), which had good traceability management. Based on the results, adjustment coefficients of 1.31 and 2.55 years/1 m for Zelkova serrata and Pinus densiflora, respectively were derived. The pith position and the number of estimated annual rings to the pith were estimated based on a arcs table and the width of the innermost rings in the increment core. Estimation results confirmed that owing to severe rotting of the stem interior, the estimation error increased as the estimated distance to the pith increased.
According to the aforementioned study results, it could be concluded that the estimation of tree age based on tree-ring observation is certainly better than others based on the number of nodes in stems and the diameter at breast height, so that it is required to establish local master chronologies representing other tree species and also regions. And more, in order to improve the accuracy of tree age estimation using resistograph, the method to identify false rings, narrow rings, and real tree rings in the measurement values by it will be fulfilled. Such study will contribute in estimating the tree age minimizing any damage to the tree stem.