A total of 451 taxa (413 species, 6 subspecies, 30 varieties, and 2 forms) in 102 families 294 genera of vascular plants growing on Aphaedo Island were identified, including 13 species of ferns (in 10 families 11 genera), 7 species of gymnosperms (in 2 families 4 genera), and 431 taxa (393 species, 6 subspecies, 30 varieties, and 2 forms) of angiosperms in 90 families 279 genera (Table 2, Appendix 1). This is equivalent to 10.1% of 4,455 taxa of the Korean Peninsula (National Institute of Biological Resources, 2017), 35.5% of 1,271 taxa of vascular plants distributed in the southern coastal district of Korea (Oh et al., 2004), and 32.7% of 1,379 species of vascular plants known to be distributed in southwestern islands in Korea (Oh et al., 2010). A total of 586 taxa (species and infra-specific taxa) have been reported from Aphaedo Island, including 154 taxa by Park (2004), 68 taxa by Kim (2008), 102 taxa by Jeong et al. (2011), 383 taxa by Nam et al. (2012), and 287 taxa by Hwang et al. (2013). Compared to previous studies, 119 taxa were newly identified in this study. Thus, a total of 705 taxa (635 species, 8 subspecies, 58 varieties, and 4 varieties) in 117 families 390 genera of vascular plants have been reported in Aphaedo Island so far, including the 119 taxa identified in the current study. Among them, cultivated plants were 25 taxa (species and infra-specific taxa), including Ginkgo biloba L., Castanea crenata Siebold & Zucc. and Lagerstroemia indica L. etc.. Excluding cultivated plants reported in this study and previous studies, 680 taxa (611 species, 8 subspecies, 57 varieties, and 4 varieties) belonging to 110 families 373 genera of vascular plants are found to be native to Aphaedo Island (Appendix 1).

Among vascular plants identified in this study, evergreen broad-leaved trees were 11 taxa: Quercus salicina Blume, Camellia japonica L., C. sasanqua Thunb., Eurya japonica Thunb., Vaccinium bracteatum Thunb., Euonymus japonicus Thunb., Ilex crenata Thunb., Fatsia japonica (Thunb.) Decne. & Planch., Hedera rhombea (Miq.) Bean, Vitex rotundifolia L. f., and Ligustrum japonicum Thunb.. Among these taxa, Camellia japonica, Hedera rhombea, and evergreen fern species Dicranopteris linearis (Burm. f.) Underw., Pteris multifida Poir., and Cyrtomium falcatum (L. f.) C. Presl. are southern plants that are expected to grow in population size and range expansion to the north due to temperature increase caused by global climate change. These are taxa that are designated and managed by the Ministry of Environment as national climate change index species (Lee et al., 2010). In addition, halophytes growing on salt fields and sea shores including mud flats, sand dunes, and rocks (Na and Hyun, 2015) were classified into 41 taxa (species and infraspecific taxa) in 18 families 32 genera (Table 3). This corresponds to 9.1% of plants distributed on Aphaedo Island. Among these, 15 taxa such as Salsola komarovii Iljin, Suaeda japonica Makino, and Polygonum fusco-ochreatum Kom. are newly reported species in this study. Suaeda glauca (Bunge) Bunge, Suaeda australis (R. Br.) Moq., Suaeda maritima (L.) Dumort., and Salicornia europaea L. are known as representative halophyte species of Chenopodiaceae. They were found in tidal flats, salt fields, and around the marina in Garyong-ri and Sinjang-ri.

The following nine taxa are classified as Threatened (critically endangered [CR], endangered [EN], vulnerable [VU]) and near threatened (NT) category in the Red Data Book of Endangered Vascular Plants in Korea (National Institute of Biological Resources, 2012) and the Rare Plants Data Book in Korea (Korea National Arboretum, 2008): Albizia calcareous (Roxb.) Prain, Wisteria japonica Siebold & Zucc., Salomonia oblongifolia DC., Bupleurum falcatum L., Centranthera cochinchinensis (Lour.) Merr. var. lutea (H. Hara) H. Hara, Utricularia bifida L., Hololeion maximowiczii Kitam., Bletilla striata (Thunb.) Rchb. f., and Pogonia japonica Rchb. f. (Table 4). Juniperus chinensis L. belongs to VU in the Red List category. However, it is excluded from the list as it is a planted species.

Albizia kalkora (Fig. 2A) was growing in foothills of Garyong-ri coast and in hills near Bunmae-ri ranch as reported in previous studies (Park, 2004; Jeong et al., 2011; Nam et al., 2012; Hwang et al., 2013). In addition, it has been found in uninhabited islands such as Songgongsan Mountain, Godongseom Island, Dolseom Island, Odo Island, Jeongjudo Island, and Haeduseom Island which belongs to Aphaedo Island (Hwang, 2017). Wisteria japonica (Fig. 2B) was observed in Hakgyo-ri Holmaesan Mountain area. Salomonia oblongifolia (Fig. 2C) was growing on the eastern slope of Bokryong-ri opposite to Holmaesan Mountain. Bupleurum falcatum was growing together in the native area of Albizia kalkora in Bunmae-ri. Centranthera cochinchinensis (Fig. 2D), Utricularia bifida (Fig. 2E), Hololeon maximowiczii (Fig. 2G), and Pogonia japonica (Fig. 2I) were distributed on the southern slope of Songgongsan Mountain bordering Songgong-ri and Daecheon-ri. In this slope, regional indicator species and a variety of mountain wetland plants have been identified, including V grade species Utricularia racemosa Wall. ex Walp. (Fig. 2F) and IV grade species such as Scleria caricina (R. Br.) Benth. (Fig. 2H), Scleria rugosa R. Br., Rhynchospora chinensis Nees & Meyen, Scleria parvula Steud., Parnassia palustris L. var. multiseta Ledeb., Habenaria linearifolia Maxim., and so on. However, they were close to low-lying trails, causing concern about degradation of native habitat and disturbance of the ecosystem due to influx of invasive plants. There are also private forests and forests owned by families of same clan. Therefore, the possibility of habitat damage due to anthropogenic activity such as mountain clearing and installation of facilities cannot be excluded. In 2007, a bonsai park was constructed on the southern side of Songgongsan Mounatain, damaging much of the wetlands. However, in the upper area of the park, a wetland ecological garden was created and a part of it was preserved. In the future, it is necessary to conduct a detailed survey on wetlands distributed throughout Songgongsan Mountain and prepare conservation plans including designation of wetland protection areas.

A total of 59 species and infraspecific taxa were confirmed as regional indicator species distributed in Aphaedo Island, including four grade V taxa [Albizia calcora (Roxb.) Prain, Wisteria japonica Siebold & Zucc., Utricularia bifida L., Utricularia racemosa Wall. ex Walp.], six taxa in grade IV [including Polygonum fusco-ochreatum Kom., Salomonia oblongifolia DC., Centranthera cochinchinensis (Lour.) Merr. var. lutea (H. Hara), and H. Hara etc], 19 taxa in grade III [including Trichosanthes kirilowii Maxim. var. japonica (Miq.) Kitam., Cynanchum nipponicum Matsum., Bletilla striata (Thunb.) Rchb. f. etc.], four taxa in grade II, and 26 taxa in grade I. These taxa represent 13.1% of vascular plants identified on Aphaedo Island. A total of 24 taxa, including Polygonum fusco-ochreatum, Trichosanthes kirilowii, and Cynanchum nipponicum, are newly recorded regional indicator species (Table 5).

The majority of these regional indicator species in grade V and IV are endangered and rare plants of the Red Data Book of Endangered Vascular Plants in Korea (Table 4). Albizia calcora (Fig. 2A) is restricted to the western coast while Wisteria japonica (Fig. 2B) distributes relatively broad in the south coast and coastal areas in Jeollabuk-do. Both species are not currently protected by law. They are exposed to development threats because they are growing in the vicinity of villages (National Institute of Biological Resources, 2012). Polygonum fusco-ochreatum, a halophyte reported in the western coast of south Chungcheong-do, was observed around the native habitat of Albizia kalkora on the coast of Garyong-ri. Cladium chinense Nees and Scleria caricina (R. Br.) Benth. (Fig. 2H) are restricted to the southern coastal regions and islands in Korea, respectively. In this study, they were found in the south coast of Songgongsan Mountain and wetlands of south slopes, respectively.

The following endemic plants in the Korean Peninsula were identified in the survey area: Hepatica insularis Nakai, Indigofera koreana Ohwi, Lespedeza maritima Nakai, Forsythia koreana (Rdhder) Nakai, Paulownia coreana Uyeki, and Weigela subsessilis (Nakai) L. H. Bailey. This is equivalent to 1.6% of 360 species (including infraspecific taxa) of Korean endemic plants (Chung et al., 2017) (Table 6). Hepatica insularis was discovered in southern slope of Songgongsan Mountain while Indigofera koreana Ohwi was growing in the forests of Bunmae-ri and near Geumsansa Temple in Garyongri. Lespedeza maritima was distributed at the mountain foot of the north side of the Bokryong-ri Horae reservoir while Forsythia koreana (planted) was collected in the forests and farms near Horae reservoir. Paulownia coreana and Weigela subsessilis not previously reported on Aphaedo Island flora were observed in Bunmae-ri Moknaru and Songgongsan Mounatain north slopes, respectively.

A total of 52 species and infraspecific taxa (in 16 families 40 genera) examined in this study are naturalized plants. This is equivalent to 11.5% of total vascular plants in Aphaedo Island. Among these, invasive (i.e., ecosystem disturbing) plant species include Rumex acetosella L., Aster pilosus Willd., Hypochaeris radicata L., Solidago altissima L., Paspalum distichum L., and P. distichum L. var. indutum Shinners (Table 7). A total of 334 taxa of naturalized plants listed in the 1st alien species management program of the Ministry of Environment (Bang, 2014) are divided into four categories based on risk level: ecosystem risk, ecosystem risk concern, harmless to ecosystem, and unclassified. According to the risk level, naturalized plants of Aphaedo Island are classified as follows. Ecosystem risk species includs all six invasive species listed above. Ecosystem risk concern species were Phytolacca americana L., Plantago lanceolata L., and Aster subulatus Michx.. Thirteen species were included in harmless to ecosystem category while 29 species were classified in the unclassified category. On the other hand, Indigofera bungeana Walp. not inlcuded in the list of the Ministry of Environment is a plant introduced from China for landslide prevention as well as greening purpose. It was included in the list of naturalized plants of this study.

Naturalized plants (species and infraspecific taxa) surveyed in Aphaedo Island since 2003 include 11 taxa by Park (2004), 67 taxa (a total of 68 taxa are presented, of which Veronica polita Fr. subsp. lilacina (H. Hara ex T. Yamaz.) T. Yamaz. are excluded here because they are native plants) by Kim (2008), 16 taxa by Hwang et al. (2013), 10 taxa by Jeong et al. (2011), and 55 taxa by Nam et al. (2012). The total number of naturalized plants reported in Aphaedo Island reached a total of 22 families, 77 genera, 100 taxa (species and infraspecific taxa), including 12 newly confirmed ones in this study such as Malva neglecta Wallr., Aster pilosus, and Briza minor L. etc. (Tables 7, 8). This corresponds to 14.7% of 680 taxa (excluding cultivated plants) of vascular plants distributed on Aphaedo Island to date. The percentage of naturalized plants (naturalization rate) in Aphaedo Island is higher than that of Imjado Island (5.5%) (Hong et al., 2011), Dochodo Island (8.9%) (Nam et al., 2012), and Bigeumdo Island (9.6%) (Nam et al., 2012). In addition, this is higher than the average naturalization rate (7.66%) of plants in inhabited island of Jeollanam-do and the naturalization rate of plants on islands in the Yellow Sea (8.39%) (Kim et al., 2017). The naturalization rate of plants on inhabited islands has a significant positive correlation with the size of the island (Kim et al., 2017). The naturalization rate of plants on Aphaedo Island is high compared to the naturalization rate of plants on Daebudo Island (12.9%) (Lim et al., 2014) which is adjacent to the metropolitan area and under accelerated development.

Aphaedaegyo is a bridge connecting Aphaedo Island and Mokpo City. It was started in 2000 and completed in 2008. Naturalized plants of Aphaedo Island were increased by a factor of 1.4 compared to that at the beginning period of the bridge construction (11 taxa) and 9 times just before the onset (69 taxa) (Table 8). On the other hand, most of invasive plants identified in this survey were found in the vicinity of Sinjangri, the place where it was connected with the Aphaedaegyo. Aster pilosus, Hypochaeris radicata, and Solidago altissima were frequently observed near the marina and Route 2. Paspalum distichum and P. distichum var. indutum were found near the reservoir (Ohoje) located in the northwest of the Aphaedaegyo and in a nearby waterway. On the other hand, Rumex acetosella and Hypochaeris radicata were distributed sporadically along the southern slope of Songgongsan Mountain where rare plants such as Utricularia bifida, Centranthera cochinchinensis, and Pogonia japonica were found.

Once the Saecheonnyeondaegyo is open in 2018 and Amtaedo Island, Jaeundo Island, Palgeumdo Island, and Anjwado Island are connected to Aphaedo Island, it is expected that naturalized plants of Aphaedo Island will rapidly flow into these areas. Island areas are vulnerable to external influx and environmental changes due to limited habitat space (Kim et al., 2017). From this perspective, it is necessary to closely monitor the naturalized plants on these islands.