atmosphere Article The Role of Aging and Wind in Inducing Death and/or Growth Reduction in Korean Fir (Abies Koreana Wilson) on Mt. Halla, Korea Jeong-Wook Seo 1,*, En-Bi Choi 2, Jun-Hui Park 2, Yo-Jung Kim 1 and Hyo-In Lim 3 1 Department of Wood & Paper Science, Chungbuk National University, Chungbuk 28644, Korea; [email protected] 2 Department of Forest Product, Chungbuk National University, Chungbuk 28644, Korea; [email protected] (E.-B.C.); [email protected] (J.-H.P.) 3 Forest Bioinformation Division, National Institute of Forest Science, Suwon 16631, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-(0)43-261-2543 Abstract: The purpose of this study was to investigate the role of strong winds and aging in the death and/or decline in the growth of Korean fir on Mt. Halla in Korea. Bangeoreum (BA-S), Jindalrebat (JD-E), and Youngsil (YS-W) on the southern, eastern, and western slopes of Mt. Halla (ca. 1600 and 1700 m a.s.l.) were selected for the study. The site chronologies were established using more than 10 living Korean firs at each site. Additionally, to date the years and seasons of death of standing/fallen dead Korean firs, 15/15, 14/15, and 10/10 trees were selected at BA-S, JD-E, and YS-W, respectively. After adjusting the age with the period of growth up to the sampling point, the oldest Korean fir found among the living trees was 114 years old at JD-E and the oldest fir among the dead trees was 131 years old at JD-E. Besides this, most of the trees at BA-S and JD-E were found Citation: Seo, J.-W.; Choi, E.-B.; Park, to have died between 2008 and 2015, and at irregular intervals between 1976 and 2013 at YS-W. J.-H.; Kim, Y.-J.; Lim, H.-I. The Role of Also, the maximum number of trees, that is, 62.7% died between spring and summer, followed by Aging and Wind in Inducing Death 20.9% between summer and autumn, and 16.4% between autumn of the current year and spring of and/or Growth Reduction in Korean the following year. Abrupt growth reductions occurred at BA-S and JD-E, and have become more Fir (Abies Koreana Wilson) on Mt. significant in recent years, whereas at YS-W, the abrupt growth reduction and recovery occur in Halla, Korea. Atmosphere 2021, 12, a cyclic order. The intensity and frequency of the typhoons increased from 2012, and this trend 1135. https://doi.org/ was in-line with the increased number of abrupt growth reductions at BA-S and JD-E. Therefore, 10.3390/atmos12091135 the typhoons of 2012 are considered as the most likely influencing factor in death and/or growth Academic Editor: Chuixiang Yi reduction in Korean firs. In contrast, the decline in the growth of the Korean firs located on the windward slope (YS-W) showed a relationship with winds stronger than 25–33 m/s. Received: 29 July 2021 Accepted: 31 August 2021 Keywords: Korean fir; tree rings; tree mortality; growth reduction; climate effect; heavy wind Published: 3 September 2021 Publisher’s Note: MDPI stays neutral 1. Introduction with regard to jurisdictional claims in published maps and institutional affil- The excellent adaptability of trees to the ever-changing regional and/or local climate iations. has led to their wide geographical distribution [1–3]. Also, tree growth depends upon climate [4]. Various studies have reported that trees at high elevations face mortality and/or reduced growth due to climate changes, such as warming, drought, or unexpected natural events caused by warming [5–8]. In particular, trees in alpine and subalpine regions are highly sensitive to climatic conditions, and because of this, any shift in their range can Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. be related to climate change [9,10]. This article is an open access article Korean fir (Abies koreana Wilson), one of the endemic subalpine tree species in the ◦ 0 ◦ 0 distributed under the terms and Republic of Korea, is distributed above 1000 m a.s.l. (ca. 35 40 and 33 50 N) on Mt. conditions of the Creative Commons Halla, Jiri, Deogyu, Gaya, Baegun, Yeongchuk, Geumwon, and Songni [11–13]. Due to Attribution (CC BY) license (https:// the moisture stress caused by warming and/or additional stresses caused by strong wind creativecommons.org/licenses/by/ and heavy snow, the number of Korean firs has decreased so markedly [14–18] that the 4.0/). Atmosphere 2021, 12, 1135. https://doi.org/10.3390/atmos12091135 https://www.mdpi.com/journal/atmosphere Atmosphere 2021, 12, 1135 2 of 13 species had been listed as “Endangered” in the RED LIST of the International Union for Conservation of Natural Resources (IUCN) [19]. Mt. Halla, which is located on Jeju Island, is a UNESCO Biosphere Reserve and World Heritage Site and also the highest mountain (1950 m a.s.l.) in the Republic of Korea. The mountain has important ecological value due to its wide biological diversity [20,21]. The mountain range is also home to the largest pure Korean fir forests in the Republic of Korea [22]. However, over the last 10 years, the number of Korean firs on Mt. Halla has severely declined from 738.3 ha in 2006 to 626.0 ha in 2015 (by 15.2% and 112.3 ha) [14,23]. Although spring drought has been declared as the main factor influencing the decline of the Korean fir on Mt. Halla [18,24,25], strong winds and aging have also been considered as potential drivers of the decay. Jeju Island is a volcanic island and is well known for the strong wind and typhoons that come from the Pacific Ocean, mainly in the summer [26]. During winter, Jeju Island is strongly affected by winter cold-air masses from Siberia, and during summer, it is affected by monsoons and tropical cyclones (typhoons) from the Pacific Ocean that bring heavy rainfall and strong winds predominantly blowing from the southwest [27,28]. Strong wind at high elevations is a stress factor for tree growth because it triggers all sorts of detrimental actions, such as the falling of leaves, breaking of branches, shaking of the root system, or removal of snow, which acts as a water reservoir for the tree growth in spring [29–31]. Therefore, a better understanding of the effects of strong winds on tree growth would help to diagnose the reasons for tree death and/or the decline in their growth. Tree-ring monitoring of Korean fir [24,32–36], even with the oldest looking trees, has revealed that this species does not live for hundreds of years [23]. According to the records published to-date, the oldest Korean fir was 235 years old [17]. In most cases, the ages at breast height were less than 100 years old. Therefore, the Korean fir is considered to live for only a hundred years [27]. Korean firs belong to the Abies species, which have a relatively short life span [37]. The purpose of the current study was to further investigate the role of strong winds and aging, the primary influencers, in the death and/or decline in the growth of Korean fir on Mt. Halla. To this end, the year of death and abrupt growth reduction in the Korean fir on Mt. Halla were analyzed using the tree-ring technique. The results of such an analysis will help to improve our understanding of the various causes of the death and/or decline in growth of the Korean fir on Mt. Halla. 2. Materials and Methods 2.1. Study Sites and Sampling in the Field Study sites were selected on the southern (Bangaeorum: BA-S), eastern (Jindalrebat: JD-E), and western (Youngsil: YS-W) slopes of Mt. Halla on Jeju Island (Figure1) at elevations between ca. 1600 and 1700 m a.s.l. (Table1). Mt. Halla is the tallest national park with a height of 1950 m a.s.l. (Baekrokdam) in the Republic of Korea. Jeju Island has a humid subtropical climate characterized by hot humid summers and cool winters due to the influence of the East Asian monsoon [26]. The annual mean temperature and total precipitation calculated for the last 32 years (1988–2020) from the meteorological stations located at the east, west, south and north of Jeju Island were 16.1 ◦C (14.4–17.8 ◦C) and 1657 mm (697–2971 mm), respectively (Figure2). The warmest and coldest months are August and January with a mean temperature of 26.8 ◦C (23.7–29.4 ◦C) and 6.2 ◦C (2.3–9.4 ◦C), respectively, and the wettest and driest months are August and December with precipitation of 272 mm (39–927 mm) and 55 mm (2–191 mm), respectively. Approximately 42.7% of the precipitation occurs in the summer (June–August). Atmosphere 2021, 12, 1135 3 of 13 Atmosphere 2021, 12, 1135 3 of 14 ■ FigureFigure 1. 1.Location Location of of the the study study sites sites ( (□)) on on Mt. Mt. Halla Halla and and the the meteorological meteorological stations stations ( ( ).). Baeck-Baeck- rokdam (▲) is the peak of Mt. Halla. rokdam (N) is the peak of Mt. Halla. Table 1. Description of sample trees (Abies koreana) at the study sites, viz. Bangaeorum (BA-S), Jindalrae (JD-E), and AtmosphereYoungsil 2021 (YS-W)., 12, 1135 3 of 14 DBH cm Site Y Tree Condition ID N Long. (N)/Lat. €/m a.s.l. (Min.–Max.) Bangae 23.1 2019 Living BA-S-LV 18 126◦310/33◦210/1700 -orum (12.0–35.0) 21.9 (BA-S) Standing dead BA-S-SD 15 126◦310/33◦210/1694 (11.0–27.5) 19.3 Fallen dead BA-S-FD 15 126◦310/33◦210/1692 (13.0–29.0) JindalraeFigure 2.