INTRODUCTION
The Korean Peninsula, which is located at the east of the Eurasian Continent, is connected to the continent to the north and surrounded by water on three sides. Therefore, the peninsula-effect is observed in the flora of each region (Lee and Yim, 2002). Although Korea is geographically a peninsula which is known to have low diversity, plant diversity per unit area is relatively high and the distribution areas are very complicated (Kim et al., 2013). Such floristic characteristics of the Korean Peninsula are the result of an interaction between the geographical location of the peninsula and the ecological features of the distributed plant species during vegetation migration due to climate changes in the past and various inorganic environments such as climate, topography and geological features (Lee and Yim, 2002). The southwest seashore of the Korean Peninsula is a typical ria coast where an irregular and complicated coastline is formed at erosional mountains due to land subsidence, fault movement and eustatism, and there are many inhabited and uninhabited islands scattered in the nearby area. In regards to such distinct characteristics, although the ecosystems of islands are unique due to geographical barriers and isolation, historical biological data is continuously becoming extinct due to natural and artificial damage without going through a preliminary investigation (Kim et al., 2013). Floristic data are the preliminary data for species composition analysis and plant geographical studies. It is one of the floristic survey methods that can be used for assuming on vegetation or changes in plant distribution of the Korean Peninsula in the past, and for monitoring distributional changes due to climate change (Kim et al., 2013).
The first study on Gyodongdo, an island located in the west coast of the Korean Peninsula, was conducted by Lee and Kim (1985), and they reported that the island consisted of 405 taxa; 104 families, 293 genera, 339 species, 62 varieties and 4 forms. Since then, studies have been carried out by Park (1986), Woo et al. (2007) and Lee et al. (2010). When the results of these studies are combined, the flora of Gyodongdo consists of about 909 taxa. However, this figure includes many crops of cultivation such as kidney bean, carrot, ginger and spring onion and doubtful species such as Equisetum sylvaticum L., Dryopteris varia (L.) Kuntze, Sinomenium acutum (Thunb.) Rehder & E. H. Wilson, Mercurialis leiocarpa Siebold & Zucc., Zizyphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow, Lespedeza maritima Nakai, Daucus littoralis Sm., Syringa oblata var. dilatata (Nakai) Rehder, Caryopteris incana (Thunb. ex Houtt.) Miq., Artemisia scoparia Waldst. & Kit. and Hemerocallis coreana Nakai. Like this, the floristic data of Gyodongdo are based on the study results of the 1980s. However, a significant change is expected in the flora of Gyodongdo because the data is more than 30 years old. Also, the result of the recent study was incomplete from the regional and the seasonal aspects, for it was carried out in only Mt. Hwagaesan, and the survey was not conducted in spring. Moreover, it is difficult to compare and review because the existing data do not include evidence samples, and detailed investigation is also insufficient. Accordingly, this study was conducted to secure evidence samples through field survey, create a detailed plant list and provide basic data for the preservation of the distributive characteristics and the efficient diversity of plants.
MATERIALS AND METHODS
1.Survey Site Information
Gyodongdo, an island sitting in the middle of the Western Sea of the Korean Peninsula, is located near the Southern Limit Line at the northwest of Ganghwa-gun and situated in 37° 47′north latitude, and in 126° 15′east longitude. The island belongs to Gyodong-myeon, Ganghwa-gun, Incheon Metropolitan City in terms of administrative district (Figure 1). On its north, there are Yeonbaek-gun and Gaepoong-gun of Hwanghae-do, North Korea, and on its south, it is connected to Ganghwado, the main island, through the Yeonryuk Bridge. Along with the main island, there are 15 annexed islands including Gyodongdo, Donggeomdo, Boleumdo, Seokmodo, Achado and Jumundo (Woo et al., 2007). The area of Gyodongdo is 47.16 km2 which is composed of farmland 35.42 km2, forest land 3.30 km2 and other 5.41 km2 (National Institute of Environmental Research, 2010). Most of the island is made up of schist and alluvium, and tideland and alluvial soil are formed in the Quaternary alluvion. Most of the mountainous areas are formed near Mt. Hwagaesan, a mountain in the southeast of Gyodongdo, and most of them are under 100 m below sea level. There is no natural river, and the Nanjeong Reservoir and the Gogu Reservoir were constructed to secure water to use in the reclaimed agricultural land. Reclaimed land, wetland, sandy coast, sea cliff, wave-cut platform and rocky coast show that coastal erosion and accumulated ground are formed (National Institute of Environmental Research, 2010). The island has a warm climate, but strong sea breeze activity is common because it is surrounded by the sea. Also, the temperature is low in winter, which belongs to the central west coast type, and the average temperature of the recent five years (2008~2012) is 11.1°C and the average precipitation is 1,592.3 mm (Ganghwa-gun, 2013).
Based on the flora of the Korean Peninsula, Gyodongdo's floristic division belongs to the middle province (Lee and Yim, 2002), and it corresponds to the cool temperate central area (Yim and Kira, 1975). The vegetation of the island is dominated by the tree stratum of Pinus densiflora Siebold & Zucc. forest, Quercus variabilis Blume forest and P. densiflora Siebold & Zucc.-Q. variabilis Blume mixed forest; shrub layer of Zanthoxylum schinifolium Siebold & Zucc.-Lespedeza bicolor Turcz.; herbaceous layer of Carex humilis var. nana (H. Lév. & Vaniot) Ohwi and Miscanthus sinensis Andersson. However, the natural vegetation is poor, because most of the island is cultivated into rice paddies. In addition, there are pine (Pinus spp.) and oak (Quercus spp.) mixed forests, and forests mixed with Pinus rigida Mill., Alnus japonica (Thunb.) Steud., Castanea crenata Siebold & Zucc. and Robinia pseudoacacia. L. are afforested in Mt. Hwagaesan and Mt. Sujeongsan (Lee and Kim, 1985).
2.Survey Method and Analysis
This study was conducted from May 2013 ~ November 2013, and our team collected and made every plant species that grow within the survey site into an exsiccata, and stored them in the higher plant exsiccata storage in the National Institute of Biological Resources (KB). Various ecological habitats including mountain, flatland, reservoir, reclaimed land, wetland, sandy coast and rocky roast, where various species were expected to grow, were included in the survey routes, and some places were surveyed along forest roads and roads (Figure 1, Table 1). Plant identification was performed based on the illustrated plant books of Lee (1980, 2003), Lee (1996a, b), Lee (1996, 2006), Korea National Arboretum (2004, 2008, 2011), Korean Fern Society (2005), Oh (2006), Park (2009) and Kim and Kim (2011), Chang et al. (2011), and a plant list was created based on the confirmed evidence samples. Scientific names and country names used here are in accordance with Lee et al. (2011a), and (P) was put after the country name in case of the planted taxa among the surveyed vascular plants. The vascular plant list was organized based on the classification system of Cronquist (1981), and the classes below genus were put in alphabetical order. The survey plans were organized based on endemic plants of the Korean Peninsula (National Institute of Biological Resources, 2013), endangered wild plants (National Institute of Biological Resources, 2014), red list plants (National Institute of Biological Resources, 2012), floristic regional indicator plants (National Institute of Environmental Research, 2012) and naturalized plants (Lee et al., 2011b), and they were separately marked in the total plant list (Appendix). In case of life type, this study used the classification of Raunkiaer (1934) and the classification of Numata (1970), which complemented the former.
RESULTS AND DISCUSSION
1.Species Composition of Vascular Plants
The vascular plants growing in Gyodongdo consisted of 24 taxa, 12 families, 15 genera, 22 species, 1 variety and 1 hybrid of pteridophyte; 6 taxa, 2 families, 3 genera and 6 species of gymnosperm; 423 taxa, 87 families, 252 genera, 382 species, 3 subspecies, 34 varieties, 3 forms and 1 hybrid of dicotyledon of angiosperm; 176 taxa, 17 families, 94 genera, 151 species, 2 subspecies, 18 varieties, 4 forms and 1 hybrid of monocotyledon of angiosperm (Table 2, Appendix). This corresponds to 14.5% of the total 4,338 taxa of vascular plants that grow in Korea (Lee et al., 2011a). Among the surveyed vascular plants, the top 10 diverse families were Asteraceae (78 taxa), Poaceae (76 taxa), Cyperaceae (50 taxa), Rosaceae (31 taxa), Fabaceae (30 taxa), Polygonaceae (21 taxa), Brassicaceae (18 taxa), Lamiaceae (16 taxa), Caryophyllaceae (14 taxa) and Liliaceae (13 taxa), making up 55.2% of the entire plants.
Mt. Hwagaesan and mountainous areas around it were dominated by secondary forests made up of pine (Pinus spp.) and oak (Quercus spp.), the two major tree species in the survey site. Also, the communities of Suaeda japonica Makino, Limonium tetragonum (Thunb.) Bullock, Typha angustifolia L., Phragmites communis Trin. and Zoysia sinica Hance were observed at the seashore, mud flat and the area of fresh water which includes salt. In case of the taxa with high appearance frequency by habitat, aquatic plants, Nelumbo nucifera Gaertn., Ceratophyllum demersum L., Polygonum hydropiper L., Polygonum thunbergii Siebold & Zucc., Myriophyllum spicatum L., Rotala indica (Willd.) Koehne, Trapa japonica Flerow, Sium suave Walter, Deinostema violaceum (Maxim.) T. Yamaz., Gratiola japonica Miq., Lindernia procumbens (Krock.) Borbás, Veronica peregrina L., Vallisneria natans (Lour.) H. Hara, Najas marina L. and Pseudoraphis ukishiba Ohwi, were observed in Nanjeong Reservoir and Gogu Reservoir. Also, salt plants, Atriplex gmelinii C. A. Mey., Chenopodium glaucum L., Kochia scoparia var. littorea Makino, Suaeda glauca (Bunge) Bunge, S. japonica Makino, Suaeda maritima (L.) Dumort., Carex scabrifolia Steud. and P. communis Trin., were observed in reclaimed land, wetland and sandy coast. In the rocky coast, Pinus thunbergii Parl., Euonymus japonicus Thunb., Orostachys japonica (Maxim.) A. Berger, Grewia parviflora Bunge and Themeda triandra ssp. japonica (Willd.) T. Koyama were observed, and around the ridges of exposed mountainous areas, there were Lepisorus ussuriensis (Regel & Maack) Ching, Pyrrosia petiolosa (H. Christ) Ching, Woodsia subcordata Turcz., Hylotelephium spectabile (Boreau) H. Ohba, Belamcanda chinensis (L.) DC. and Amitostigma gracile (Blume) Schltr.
As the result of comparing with the studies on the flora of Gyodongdo (Lee and Kim, 1985; Park, 1986; Woo et al., 2007; Lee et al., 2010), a total of 184 taxa including Equisetum ramosissimum Desf., Dennstaedtia wilfordii (T. Moore) H. Christ, W. subcordata Turcz., Asarum mandshuricum (Maxim.) M. Kim & S. So, Clematis patens C. Morren & Decne., Papaver rhoeas L., Corydalis turtschaninovii Besser, K. scoparia var. littorea Makino, Silene aprica Turcz. ex Fisch. & C. A. Mey., Polygonum plebeium R. Br., Viola mandshurica f. hasegawa Hiyama, Salix koriyanagi Kimura ex Goerz, Lepidium sativum L., Lysimachia davurica Ledeb., Duchesnea indica (Andr.) Focke, Pyrus calleryana var. fauriei (C. K. Schneid.) Rehder, Rubus fruticosus L., Astragalus sikokianus Nakai, R. indica (Willd.) Koehne, Koelreuteria paniculata Laxm., Cnidium monnieri (L.) Cusson, Ipomoea purpurea (L.) Roth., Callitriche palustris L., Limnophila sessiliflora (Vahl) Blume, Adenophora verticillata (Pall.) Fisch., Ambrosia trifida L., Bidens pilosa L., Rudbeckia hirta var. pulcherrima Farw., Senecio argunensis Turcz., Solidago altissima L., Tradescantia ohioensis Raf., Carex cinerascens Kük., Carex dispalata Boott ex A. Gray, Carex nervata Franch. & Sav., Carex polyschoena H. Lév. & Vaniot, Carex sabynensis Less. ex Kunth, Cyperus michelianus var. pacificus Ohwi, Cyperus serotinus Rottb., Eleocharis wichurai Boeck., Schoenoplectiella hotarui (Ohwi) J. Jung & H.-K. Choi, Scleria parvula Steud., Bromus tectorum L., Elymus dahuricus Turcz. ex Griseb., Eulalia speciosa (Debeaux) Kuntze, Leersia oryzoides (L.) Sw., P. ukishiba Ohwi, Sporobolus japonicus (Steud.) Maxim. & Rendle, Allium sacculiferum Maxim. and I. ruthenica var. nana Maxim. were newly observed through this study, and ☆ is marked in front of their names in the plant list (Appendix). Meanwhile, among the unidentified taxa, there is the possibility of distribution of Osmunda cinnamomea L., Davallia mariesii T. Moore ex Baker, Ginkgo biloba L., Clematis terniflora var. mandshurica (Rupr.) Ohwi, Ulmus davidiana var. japonica (Rehder) Nakai, Silene aprica var. oldhamiana (Miq.) C. Y. Wu, Polygonum filiforme Thunb., Viola acuminata Ledeb., Astilbe rubra Hook. f. & Thomson ex Hook. f., Malus baccata (L.) Borkh., Potentilla anemonifolia Lehm., Prunus sargentii Rehder, Pyrus ussuriensis Maxim., Rubus coreanus Miq., Desmodium podocarpum ssp. oxyphyllum (DC.) H. Ohashi, Lathyrus japonicus Willd., Vicia unijuga A. Braun, Geranium sibiricum L., Rhus javanica L., Acer pictum var. mono (Maxim.) Maxim. ex Franch., Acer tataricum ssp. ginnala (Maxim.) Wesm., Aralia elata (Miq.) Seem., Rubia akane Nakai, Dendranthema zawadskii var. latilobum (Maxim.) Kitam., Eupatorium japonicum Thunb. and Synurus deltoides (Aiton) Nakai, which are already recorded in the above papers. However, because the lists in the existing documents do not include evidence samples and specify where samples are stored, it is virtually impossible to compare and review.
The plant list of this study is based on the evidence samples, and the number of its taxa is thought to be smaller than that of actually distributed taxa. Also, if additional study is carried out on various routes and different seasons, it will be possible to find new species or those with a possibility of distribution.
2.Korean Endemic Plants
In case of Korean endemic plants that were identified in this site, there were 9 taxa, 8 families and 9 genera: Clematis brachyura Maxim., Salix koriyanagi Kimura ex Goerz, Viola seoulensis Nakai, Populus × tomentiglandulosa T. B. Lee, Rhododendron mucronulatum Turcz., Geranium koreanum Kom., Forsythia koreana (Rehder) Nakai, Hemerocallis hakuunensis Nakai (Figure 2D) and Lilium amabile Palib. (Oh et al., 2005; National Institute of Biological Resources, 2013). Among them, S. koriyanagi Kimura ex Goerz, R. mucronulatum Turcz., G. koreanum Kom., L. amabile Palib. and H. hakuunensis Nakai are taxa which are observed in neighboring countries. Therefore, some researchers and papers doubt whether they are truly Korean endemic plants (Oh et al., 2005; Chang, 2007; Park, 2007a; Park, 2007b). Accordingly, four taxa are the ones without controversy, and by integrating Hwang and Kim (2012)'s opinion, the plant list is organized into 5 taxa, 5 families and 5 genera by including in H. hakuunensis Nakai (Table 3, Appendix).
C. brachyura Maxim. and H. hakuunensis Nakai were discontinuously distributed in the ridges, and V. seoulensis Nakai communities were found in lowland and flatland. P. × tomentiglandulosa T. B. Lee and F. koreana (Rehder) Nakai were planted around the village as street trees and ornamental trees.
3.Endangered Wild Plants and Red List Plants
Through this study, I. ruthenica var. nana Maxim. (Figure 2F), which is a Class II endangered wild plant legally protected in accordance with the⌈Wildlife protection and management Act⌋, was observed (Table 4). They are widely distributed in the lowlands in Gyeonggi-do, Gangwon-do, Daegu and Chungcheongnam-do, but they are currently in danger of extinction due to various development projects carried out in their habitats. They were found in Seoul and Gyeonggi-do in the past, but not in recent surveys (National Institute of Biological Resources, 2012). In three of their habitats in Gyodongdo, some 30 individuals were observed: two habitats in Mt. Hwagaesan and one in Mt. Bonghwangsan. They were all distributed in sunny places, but because those places were near graves and trails, there is a possibility of damages due to mowing and stamping. Although environment of their habitats is not stable, their growth condition is good and should be steadily monitored. Also, because there are records that stated that I. ruthenica var. nana Maxim. was observed in nearby islands such as Maldo and Jumundo (Park, 1990a; Park, 1990b), more study needs to be conducted in those islands. Until now, their southernmost habitat is known to be Daegu, but the information was revised to the Southern Limit Line as their habitat was newly found in the coastal area of Jeollanam-do (National Institute of Biological Resources, 2014). In addition, their habitats were also observed in Gimpo, Gyeonggi-do, a city in the capital area. Such study results are expected to contribute to the establishment of an endangered wild plant distribution map.
Among the vascular plants on the red list of the National Institute of Biological Resources, this study identified 13 taxa, 10 families and 13 genera (Table 4, Appendix): P. yedoensis Matsum. of endangered (EN) species; U. pilosa (Makino) Makino and I. ruthenica var. nana Maxim. of Vulnerable (VU) species; S. argunensis Turcz. of Near Threatened (NT) species; Platycladus orientalis (L.) Franco, Potentilla discolor Bunge, L. sessiliflora (Vahl) Blume, Acorus calamus L., Phacelurus latifolius (Steud.) Ohwi, P. ukishiba Ohwi (Figure 2C), Belamcanda chinensis (L.) DC. of Least Concern (LC) species and; A. sikokianus Nakai (Figure 2A) and Potamogeton oxyphyllus Miq. of Not Evaluate (NE) species. Among them, P. yedoensis Matsum. and P. orientalis (L.) Franco were thought to be not so meaningful because they were planted. Also, a small number of P. discolor Bunge individuals were observed in lowlands, and some A. sikokianus Nakai individuals were found in the Wolseon Port trail. L. sessiliflora (Vahl) Blume was a subdominant species in the paddy fields at the foot of Mt. Yuldusan, and some U. pilosa (Makino) Makino were also observed in this area. S. argunensis Turcz. and B. chinensis (L.) DC. were observed at the ridge of Mt. Hwagaesan, and P. oxyphyllus Miq. and P. ukishiba Ohwi were observed in Nanjeong Reservoir and Gogu Reservoir respectively. Some 20 A. calamus L. individuals were observed in the puddle (irrigation pond) at the entrance of the trail in Mt. Hwagaesan in Daeryong-ri, and P. latifolius (Steud.) Ohwi community was distributed in the causeway (embankment road) under Nanjeong Reservoir.
Only a small number of individuals of endangered wild plants and red list plants were observed in Gyodongdo and their habitats were unstable. Therefore, the preservation of those habitats and the distribution of those plants in neighboring areas need to be carried out, because they may lose their habitats to other plants or die out after failing to adapt to changes in the environment.
4.Floristic Regional Indicator Plants
A total of 47 taxa, 36 families and 45 genera (Table 5, Appendix) of floristic regional indicator plants were identified, and as for Grades Ⅴ~Ⅳ, the closely examined species, a total of seven taxa including P. yedoensis Matsum., A. sikokianus Nakai, U. pilosa (Makino) Makino, P. ukishiba Ohwi and I. ruthenica var. nana Maxim. were surveyed. In case of Grade III, nine taxa including W. subcordata Turcz., Rhodotypos scandens (Thunb.) Makino, K. paniculata Laxm. and L. sessiliflora (Vahl) Blume were observed in the survey site. Besides them, 10 taxa of Grade II and 21 taxa of Grade I were identified. Among them, R. scandens (Thunb.) Makino., Koelreuteria paniculata Laxm., Euphorbia esula L., Grewia parviflora Bunge, Chloranthus fortunei (A. Gray) Sloms and E. japonicus Thunb. were southern plants, making them highly valuable from the academic aspect when discussing their plant-geographical and chorological value. A small number of R. scandens (Thunb.) Makino and Chloranthus fortunei (A. Gray) Sloms were observed in the valley of Hwagye Temple in Mt. Hwagaesan. Also, only one K. paniculata Laxm. individual was growing at the seashore near the Wolseon Port trail, and this is thought to be because a seed which had flown in along the sea current has settled down. Five individuals of E. esula L. were observed in a sunny place at the foot of Mt. Bonghwangsan.
Based on the flora of the Korean Peninsula, Gyodongdo's floristic division belongs to the middle province. However, because of the above southern plants and some taxa that belong to the south of the center area such as Rubus corchorifolius L. f. and Elaeagnus macrophylla Thunb., which is recorded in the existing paper, the vegetation of Gyodongdo deserves special mention. Accordingly, a follow-up study is required to identify distributive characteristics including environmental factors and the correlation with climate.
5.Naturalized Plants
There were 62 taxa, 16 families and 48 genera of naturalized plants distributed in Gyodongdo (Table 6, Appendix), and this corresponds to 9.9% of the entire 629 taxa, and the urbanization index of 19.3% of 321 taxa reported by Lee et al. (2011b). This is low compared to the urbanization index of Seoul (36%) (Yim and Jeon, 1980), but it is close to the average naturalization rate (10.3%) of Korea (Koh et al., 1995). As for the distributive characteristic by family, there were 24 taxa of Asteraceae, 6 taxa of Poaceae, 5 taxa of Convolvulaceae, 4 taxa of Brassicaceae and 4 taxa of Fabaceae.
Meanwhile, Ambrosia artemisiifolia L., Ambrosia trifida L., Aster pilosus Willd. and Solidago altissima L., which were designated as invasive alien plants according to the Act on Conservation and Utilization of Biodiversity were identified (National Institute of Environmental Research, 2013). Their common characteristics are that they are from North America, annual or perennial herbs, and they are usually distributed in places such as farmland, near road, fallow land and reservoir, where human activity is relatively high. A. artemisiifolia L., A. trifida L. and A. pilosus Willd. were easily observed near the roads in the survey site, and S. altissima L. was observed in only the surrounding areas of Binjang Port.
Alien species need to be eliminated preferentially because their seed setting rate is high, they grow well in poor soil and they are dominant in competition with native plants. Eradication need to be carried out effectively mainly in places where they grow, but they need to be observed continuously even after pulling out their roots. Also, local governments and residents should be alerted of the harm alien species can do to ecosystems, and advised to effectively prevent them from growing through steady promotion activity.
In addition, Gyodongdo used to be only reachable through ships, but since the opening of Yeonryuk Bridge in last July, a rise in the number of visitors for trekking, bicycle riding etc. is expected, thus increasing the possibility of the inflow of naturalized plants. Accordingly, an efficient plan including monitoring and regular eradication needs to be established.
6.Life Form Composition
Among the life types of 629 surveyed taxa, the dormancy form Hemicryptophytes (H) made up the highest portion of the dormancy form, followed by Therophytes (Th) 26%, Hydrophytes (HH) 13.1%, Geophyte (G) 12%, Nanophanerophytes (N) 7.3%, Megaphanerophytes (MM) 6.8%, Microphanerophytes (M) 3.3%, Chamaephytes (Ch) 3.2% and Epiphytes (E) 0.3% (Table 7, Appendix). When they are compared to the geographical distribution of the Korean life form (Yim et al., 1982), the ratio of Megaphanerophytes and Microphanerophytes including Epiphytes, Geophyte, Hemicryptophytes and Nanophanerophytes was low, and the ratio of Chamaephytes, Hydrophytes and Therophytes was high. In case of Ganghwado area, the ratio of Hemicryptophytes and Therophytes was low, and that of other taxa was the ratio of Hemicryptophytes and Therophytes was analyzed to be high (Lee et al., 2012; Kim et al., 2013). Therefore, these islands including Gyodongdo belong to the middle province, and because they are not far away from each other, they have similar flora and the life form of temperate climate regions. Meanwhile, based on the analysis on 57 areas, the life form of South Korea (Yim et al., 1982) is composed of M (20%), N (14.8%), E (7.4%), Ch (1.9%), H (30.0%), G (12.4%), HH (1.4%) and Th (19.0%), and coincided with the paper which reported that the climate is Hemicryptophytes (H) climate.
