List of palynological studies in South Korea.
The Korean Peninsula, surrounded by the sea on three sides (east, west, and south), is located on the eastern end of the Asian continent adjacent to the West Pacific and belongs to the temperate zone with four distinct seasons, which are largely controlled by the East Asian monsoon. During the winter, from December to February, it is cold and dry due to the establishment of the strong Siberian anticyclone on the Tibetan Plateau. Meanwhile, the summer, from June to August, is hot and wet, with frequent heavy rains (An, 2000; Nakagawa et al., 2006; Yancheva et al., 2007). The modern climate of Korea is characterized by a mean annual temperature of 12.2℃, ranging from 5.1℃ to 13.6℃, with a monthly mean daily maximum temperature of up to 19.4℃ and a monthly mean daily minimum temperature of 0℃ over the past 30 years (1971–2000). Precipitation is relatively high (mean, 1299 mm), and about 70% of the annual precipitation falls in summer, especially from June to August (Korean Meteorological Administration, http://kma.go.kr).
Pollen studies are well suited to examining the impact of rapid climate change on terrestrial ecosystems because the reponse of vegetation to climate fluctuation is pronounced and can occur on decadal time scales (Tinner & Lotter, 2001). Pollen analysis provides information that is unavailable from other sources and offers a unique and invaluable perspective on natural, climate-induced vegetation changes and environmental reconstruction (Birks & Birks, 1980; Davis, 1994) despite its limitations compared with marcropaleontology. Therefore, among the various terrestrial paleoclimate proxies, pollen has proven to be a most useful tool.
Pollen studies were carried out in South Korea with a focus mainly on reconstructing vegetation and climate from the Quaternary sediments of wetlands (e.g., Chang et al., 1987; Choi et al., 2005; Jang et al., 2006; Jun et al., 2010; Park & Yi, 2008; Yi et al., 2004, 2005, 2008a, 2008b; Yoon, 1997), lakes (e.g., Chang & Kim, 1982; Fujiki & Yasuda, 2004; Yasuda et al., 1980), and archaeological sites (e.g., Chung et al., 2006, 2010; Yi, 2011; Yi & Kang, 2009; Yi & Kim, 2009; Yi et al., 2011; Yoon et al., 2005). Early, non-dated pollen studies were conducted to interpret local vegetation history. Recently, pollen investigations have reconstructed vegetation and climate changes with geologic ages using radiocarbon dates.
The age-controlled pollen data are used herein. The response of vegetation in South Korea to East Asian monsoon climate change is discussed based on the pollen datasets.
2. East Asian monsoon
The East Asian monsoon is an integral part of the global climatic system. Monsoon climates, especially monsoon-derived precipitation, are important to the maintenance of the environments of East Asia. This monsoon regime is a sub-system of the Asian monsoon circulation (An, 2000). The East Asian monsoon is formed by thermal differences between the Asian landmass and the Pacific Ocean; the area to the northwest of the front is under the strong influence of the continental Siberian air mass, which is dry and has large seasonal temperature variations, whereas the area to the southeast of the front is controlled by the oceanic Pacific air mass, which is high in moisture and has small seasonal temperature variations (Yancheva et al., 2007). The coastal East Asian regions are characterized by prominent seasonality due to the seasonal migration of the monsoon front across these regions (Nakagawa et al., 2006). As the seasonal temperature variability on the continent is greater than that in the ocean, the temperature gradient between the two air masses creates a surface-air pressure gradient that seasonally changes its direction, forcing NW and SE surface winds in winter and summer, respectively (Fig. 1).
2.1. Evolution of the East Asian monsoon
The evolution of the East Asian monsoon is a principal factor controlling paleoenvironmental changes in the East Asian region (An, 2000). Cenozoic uplift of the Himalayan–Tibetan Plateau is thought to contribute to the Asian Monsoons, including the East Asian and Indian monsoons, and the Northern Hemispheric ice ages (Qiang et al., 2001). Qiang et al.’s (2001) study of the magnetostratigraphy of the Jiaxian red clay section of the Chinese Loess Plateau documented that the onset of the East Asian monsoon occurred in the Late Miocene (8.35 Ma). Moreover they recognized long-term changes in the East Asian monsoon since the Late Miocene based on accumulation rate and grain size analysis of the eolian dust deposited in the central Chinese Loess Plateau. For example, the strengthening of the East Asian winter monsoon occurred between 3.5 Ma and 3.1 Ma and intensified further after 2.6 Ma. However, Sun and Wang (2005), based on compilation of paleobotanical and lithological data from China, suggested that an initiation of monsoon climate system in East Asia was further back to the latest Oligocene. Subsequently, paleomonsoonal studies have used multi-proxies of loess–paleosols (e.g., An, 2000; An et al., 1990), caves (e.g., Dykoski et al., 2005; Wang et al., 2001), lake sediments (e.g., Nakagawa et al., 2006; Wu et al., 2006; Wűnnemann et al., 2006; Yamada, 2004), ice cores (e.g., Yao et al., 2001), and pollen (e.g., Feng et al., 2006; Makohonienko et al., 2008; Yi et al., 2003a, 2003b).
2.2. Modern climate of Korea
South Korea is in the temperate zone controlled by the East Asian monsoon, which is characterized by distinct seasonal changes, with a warm, wet summer and a cool, dry winter. However, the present climate conditions are trending toward increases in extreme precipitation and drought.
Baek and Kwon (2005) showed a decreasing trend in April precipitation and an increasing trend in August precipitation for 1954–2002. Chang and Kown (2007) investigated the spatial patterns of trends in summer precipitation for 1973–2005 and pointed out a significant increase in June precipitation for the northern and central-western part of Korea. Bae et al. (2008) reported that the long-term trends in annual precipitation and runoff were increasing in the northern part of Korea and decreasing in the southwestern part of Korea. Furthermore, a recent study on climate trends in Korea reported annual precipitation increases and increases in the number of severe precipitation events (Jun et al., 2010). It showed that the increase in annual precipitation is mainly associated with increases in the frequency and intensity of heavy precipitation during the summer season (June–September), whereas precipitation during the spring and winter seasons showed a decreasing trend. This variation in precipitation is likely to increase flood and drought risk.
3. Vegetation of Korea
The first studies of Korean plants were made by Japanese researchers (e.g., Nakai, 1952; Uyeki, 1911, 1933), followed by Korean botanists (e.g., Chung & Lee, 1965; Kong, 2007; Lee, 1985; Lee & Yim, 2002; Yim, 1977; Yim & Kira, 1975). Yim and Kira (1975) first established a vegetation map of the Korean Peninsula, which consists of conifer forest (subalpine zone), deciduous broadleaved forest (temperate zone), and evergreen forest (subtropical zone). The deciduous broadleaved forest is further divided into three zones at different latitudes: the northwest temperate zone, the central temperate zone, and the southern temperate zone. Moreover, the vertical vegetation zone is divided on the basis of the elevation of mountain ranges. Local vegetation is primarily controlled by climate, soil, geomorphology, and artificial factors. In all, the distribution of Korean forests is band-shaped and changes with variations in temperature depending on latitude and elevation (Fig. 2).
Temperature is an important factor in the growth and distribution of plants. The mean annual temperature in Korea is 2.5–10.0℃ in the northern region (39°N–43°N), 10.0–12.5℃ in
the central region (37°N–39°N), and 12.5–15.0℃ in the southern region (33°N–37°N). The mean monthly daily maximum temperature is 32.5–35℃ in the northern region and 37.5–40.0℃ in the southern region; the mean daily minimum temperature ranges from -5℃ to -15℃ in the subtropical region, -15℃ to -20℃ in the warm-temperate south central region, -20℃ to -25℃ in the warm-temperate central region, -25℃ to -30℃ in the warm-temperate north central region, and -35℃ to -45℃ in the subalpine northern region (Kong, 2007). Subalpine conifer forest is mainly distributed in North Korea and consists of evergreen conifers, such as a fir (
Mixed conifer and deciduous broadleaved forests are dominated by pines (
Deciduous broadleaved forest (DBF) is distributed between 35°N and 43°N, except in the subalpine area. The main trees are maples (
Subtropical evergreen forest is located along the south coast and is limited to 35°N in inland areas and 35°30’N in coastal areas, including several islands. The main components are trees such as
Additionally, coastal conifers such as
4. Palynological studies in South Korea
Quaternary palynological studies in Korea have mainly focused on the reconstruction of vegetation and climate change since the last glacial maximum (LGM). In the middle to late 20th century, Korean pollen investigations were carried out in peat or organic-rich soil from coastal wetlands or lagoons (e.g.,., Jo, 1979; Oh, 1971; Park, 1990; Tsukada, 1977; Yi et al., 1996; Yoon, 1997). Subsequently, a number of palynological studies were performed due to increased peat layer recovery from excavations of inland wetland and archaeological sites (e.g., Chung & Lee, 2006; Kim et al., 2001; Seo & Yi, 2001; Yi et al., 2006, 2008a). Attempts were made to reconstruct the natural vegetation history in response to climate change from the peat and wetland samples and to intrepret human-induced changes based on age-controlled pollen profiles, (agriculture and land-use in forests). The palynological studies are shown in Table 1.
Two Holocene pollen analyses are introduced herein: the Paju-Unjeong site is located in the west central area, and the Pyeongtaek site is located in the western coastal area on the Korean Peninsula (Fig. 2).
4.1. Pollen assemblages of the Paju-Unjeong area
Zone UJ10-I (elevation 17.954–18.164 m a.s.l., ca. 8425–4700 cal yr BP) was quantitatively dominated by
Zone UJ10-II (elevation 18.164 –18.354 m a.s.l., ca. 4700–2170 cal yr BP) was characterized by the dominance of
Zone UJ10-III (elevation 18.354–18.764 m a.s.l., ca. 2170 cal yr BP–Modern) was conspicuously marked by the growing dominance of
|Lake||Yongrangho||Socho-shi, Gangwon Province||Tsukada (1977), Chang & Kim (1982)||Holocene|
|Hyangho||Gangneung-shi, Gangwon Province||Fujiki & Yasuda (2004)||Holocene|
|Bangeojin||Ulsan-shi, Gyeongsang Province||Jo (1979), Chang & Kim (1982)||Holocene|
|Wolhamji||Buyeo-gun, Chungcheong Province||Chang & Kim (1982)||Holocene|
|Moor, Bog||Mt. Daeam||Inje-gun, Gangwon Province||Chang et al. (1987), Choi & Koh (1989)||Holocene|
|Moojaechi||Ulsan-shi, Gyeongsang Province||Park & Chang (1998), Choi (2001)||Holocene|
|Wetland||Youngyang Basin||Yongyang-gun, Gyeongsang Province||Yoon & Jo (1996)||Late Pleistocene-Holocene|
|Hanam||Hanam-shi, Gyeonggi Province||Yi et al. (2008b)||Late Pleistocene-Holocene|
|Paju-Unjeong||Paju-shi, Gyeonggi Province||Yi et al. (2011)||Holocene|
|Coastal wetland||Imja-do||Shinan-gun, Jeolla Province||Yi et al. (2004)||Holocene|
|Cheollipo||Taean-gun, Chungcheong Province||Park (1990), Jang et al. (2006)||Holocene|
|Ilsan||Goyang-shi, Gyeonggi Province||Yoon (1997), Yi et al. (2005)||Holocene|
|Pyeongtaek||Pyeongtaek-shi, Gyeonggi Province||Oh (1971), Jun et al. (2010)||Holocene|
|Archaeo-logical site||Sorori||Cheongwon-gun, Chungcheong Province||Kim (2001)||Late Pleistocene|
|Unjeonri||Cheonan-shi, Chungcheong Province||Park (2004)||Holocene|
|Anyoungri||Tacheon-myeon, Chungcheong Province||Seo & Yi (2003)||Late Pleistocene|
|Poonggi||Asan-shi, Chungcheong Province||Yi et al. (2006)||Late Pleistocene|
|Yongdong||Naju-shi, Jeolla Province||Chung & Lee (2006)||Late Pleistocene|
|Yeanri||Gimhae-shi, Gyeongsang Province||Yi & Saito (2003c)||Holocene|
|Cheonggye-cheon||Seoul||Yi et al. (2008a)||Holocene|
|Jinju||Jinju-shi, Gyeongsang Province||Chung et al. (2006)||Late Pleistocene|
|Piseori||Muan-gun, Jeolla Province||Chung et al. (2005)||Late Pleistocene|
|Island||Hanon||Seogyuipo-shi, Jeju Province||Chung (2007)||Late Pleistocene|
4.2. Pollen assemblages of the Pyeongtaek area
Zone HS-I (depth 192–187 cm, ca. 10 600 to ca. 10 400 cal yr BP) was dominated by
Zone HS-II (depth 187–122 cm, ca. 10 400 to ca. 8000 cal yr BP) was defined by a distinct increase in
Zone HS-III (depth 122–77 cm, ca. 8000 to ca. 6000 cal yr BP) was characterized by the sudden expansion of T-C-C (Taxaceae-Cephalotaxaceae-Cupressaceae) and Cyperaceae compared with zone HS-II.
Zone HS-IV (depth 77–44 cm, ca. 6000 to ca. 4500 cal yr BP) was marked by the predominance of
5. Vegetation change and the East Asian monsoonal fluctuation in South Korea during the Holocene Period
5.1. Vegetation changes
The available age-controlled pollen datasets allow us to infer the vegetational history of South Korea. The vegetation changes in the eastern and western parts of South Korea are discussed. During the early Holocene (10 000–7000 cal yr BP), subalpine conifer forest was replaced by broadleaved deciduous forest dominated by hardwood oak trees due to climatic amelioration. Moreover, the forest components evidenced by the pollen records are greater than those of the preceding period. During the mid-Holocene optimum, the former forest was replaced by a mixed subtropical and warm-temperate broadleaved forest, which was characterized by evergreen oak and thermophilous hardwood trees. These trees were composed mainly of oak
Compared with the east coast, pollen studies from the west coast are more numerous (e.g., Jang et al., 2006; Jun et al., 2010; Oh, 1971; Park, 1990, Yi et al., 2005; Yi et al., 2010; Yoon, 1997) because there are a plenty of wetlands along this coast. From 8000 to 5000 cal yr BP, subtropical evergreen and warm-temperate forest occupied this area, especially the hills and low mountainous areas, resulting in a high proportion of pollen from trees and shrubs with a smaller proportion from herbs. The evergreen and warm-temperate forest consisted mainly of oak [
Korea Meteorological Administration (KMA) reports that there was a mean annual temperature of 12.2℃ and 1255 mm in a mean annual precipitation during the 1973–1980, but the temperature and precipitation increased up to 12.9℃ and 1469 mm, respectively, between 2001 and 2007. This meteorological phenomena show the climate conditions of Korea are changing to be subtropical zones caused by global warming. With such climate conditions, types and communities of Korean forest can be expected to change. For example, a Korean fir (
In summary, the Holocene pollen records reflect differences in forest plant assemblages between the western and eastern regions during the early to middle Holocene. In the eastern coastal area, dominance alternated between oak and pine over time, reflecting climate changes during the early to middle Holocene. However, in the western coastal area, oak and alder were co-dominant taxa during the early to middle Holocene. This is a reflection of the geomorphic features of and the marine environmental influence over the Korean Peninsula. The Korean Peninsula is geomorphologically highly mountainous in the east and flat, low, and wide in the west (Fig. 2). During the early to middle Holocene, the west coast experienced wetter conditions for a longer period of time than did the east coast during sea-level rise. From the late Holocene (ca. 2000 cal yr BP), pine trees and agricultural indicators increased over South Korea, reflecting the intensity of human impact since that time (Fig. 6). Due to global warming, no subalpine conifer, especially a Korean fir (
5.2. Vegetation responses to turbulent East Asian monsoonal changes during the early to middle Holocene
About 9000 cal yr BP, the concentration of CO2 (up to 380 ppm) reached a maximum in the atmosphere along with increased solar radiation in the Northern Hemisphere in the summer (Berger, 1978; Neftel et al., 1982). In July, solar radiation was 7% higher than at present. As a result, the seasonal range of temperatures was considerably increased. The difference in warming between the continent and ocean was higher, leading to monsoons (Kutzbach, 1981; An et al., 2000; Shi et al., 2011). The majority of thermophiles, particularly evergreen trees, did not grow well because of cold winters, even though summers were relatively warm. This is why deciduous oak forests were so common in South Korea during the early Holocene.
From the mid-Holocene optimum, the percentage of broadleaved deciduous components gradually decreased, whereas the percentage of pollen grains from evergreen oak [
Pollen studies in China indicate that forest vegetation occupied a larger area during the mid-Holocene (Yu et al., 1998, 2000) due to warm and wet climate together with greater than present summer insolation and stronger Pacific monsoon activity (Winkler & Wang, 1993). The oak-pine woodland and steppe were replaced by a dry steppe vegetation in northeast China region after late Holocene of ca. 3500 cal. yr BP (Liu et al., 2002; Tarasov et al., 2006).
Takahara et al. (2000) concluded that the vegetation distribution at mid-Holocene time (6000 yr BP) was rather similar to present. From their pollen study, they pointed out the broadleaved evergreen and warm mixed forest may have been present at higher elevations in the mountains of central Japan. But, the northern limit of the biome was apparently similar to present as a consequence of northward migration of the biome under warmer and wetter conditions.
The Korean Peninsula, surrounded by the sea on three sides (east, west, and south), is located on the eastern end of the Asian continent and belongs to the temperate zone with four distinct seasons largely controlled by the East Asian monsoon. During the summer, the Korean Peninsula is occupied by a subtropical high pressure system and experiences warm, wet conditions with frequent, heavy rainfalls. During the winter, it is cold and dry under the dominant influence of the northwesterly Siberian high air mass. The Korean Peninsula is an area sensitive to climate changes. Therefore, well-preserved records from the Korean Peninsula that provide a continuous climate history are a source of valuable information of the East Asian monsoonal system.
Age-controlled pollen stratigraphy was obtained from several organic-rich sediments in wetlands and archaeological sites in South Korea. Holocene vegetation and climate were deduced from pollen records. During the Early Holocene (ca. 10 400−8000 cal yr BP), dry, cool-temperate conditions encouraged
Owing to global warming, no subalpine conifer, especially a Korean fir (Abies koreana), will be exist in South Korea in near future. Also evergreen broadleaved forest will further spread north to N 37°, and south temperate zone of deciduous broadleaved forest will occupy the region of central temperate zone of deciduous broadleaved forest.
This study was supported by the basic research project of the Korean Institute of Geosciences and Mineral Resources (KIGAM). The pollen datasets were a partly result of this project.