Vascular plant diversity of the Gogunsan Archipelago in the Korean Peninsula

Abstract

This study was carried out to investigate the flora of six islands belonging to the Gogunsan Archipelago (i.e., Sinsi-do, Seonyu-do, Munyeo-do, Yami-do, Bian-do, and Duri-do) in the Korean Peninsula. As results of five field surveys from March to October of 2016, we have identified 575 total taxa, representing 527 species, five subspecies, 42 varieties, and one hybrid, placed in 358 genera and 118 families. Of these 575 taxa, four are endemic to Korea, six taxa are listed on the Korean Red List of threatened species, 67 are floristic regional indicator plants, and 74 are invasive alien species. In this study, we compared species richness among the islands, and find that the larger the islands, the higher the species richness. In the case of habitat affinity types, forest species were most common, followed by farmland, seacoast, bare ground and wetland species. From similarity analyses based on the composition of vascular plants, each island did not exhibit either local specificity or unique diversity. On the contrary, the proportion of invasive alien and ruderal species may increase by human activities. Investigations and analyses of island flora such as this are important to assess the current status of the flora, predict future vegetation patterns and the spread of the alien species, and establish managment plans of plant diversity.

Introduction

The Korean Peninsula, located in the eastern portion of the Eurasian continent, is connected to the continent to the north and surrounded by seawater on three sides(Kim et al., 2015). Since Korea is located at the intersection of vascular plants with southern and northern distribution limits, plant diversity is relatively high per unit area and distributions are very complex. These features of Korean flora are thought to be results of correlations between ecological characters of plants and abiotic elements of climate, geographical features, and geographical location (Lee and Yim, 2002). The southwestern coast of the Korean Peninsula is a typical Rias coast with irregular, complex coastlines formed by erosion, fault activities, and sea elevation, and thus many inhabited and uninhabited islands are scattered nearby. A lot of islands are scattered along western and southern coasts of the peninsula (Cho, 2002), and the present flora of these islands follow the peninsula effect being impoverished in species composition from the mainland to the adjacent islands or outer edge of the peninsula (Lee and Yim, 2002). In the last glacial maximum (some 12,000-18,000 years ago), the current western and southern coasts were land associated with continents, but after the ice age was over, some areas with high elevation became islands caused by the rising sea level. Scholars estimate that the current coastline formed some 8,000 to 10,000 years ago so that plants remaining on the southwestern coastal islands could be isolated from the population of the continent for more than 8,000 years(National Institute of Biological Resources, 2015). There is a possibility of genetic interaction between peninsular and inland populations depending on pollination and seed dispersal capabilities, but islands located far from shore show unique ecosystem because of geographical barriers and isolation. It is also known that the island forms an independent ecological landscape and is biologically localized where the introduction, settlement, and extinction of species is more variable than that of mainland (Kim et al., 2016). It is a common that the closer the island is to the mainland and the larger its area, the higher species richness(Kong, 2007). Currently, about 4,000 inhabited and uninhabited islands are scattered around the southwestern coast of Korea (Kim et al., 2016). Although the islands, which forms their own ecosystem based on interactions between terrestrial and marine ecosystems, are highly valued area in terms of ecological, biological, and genetic conditions, not much progress has been made in domestic research on these issues (Kim et al., 2016). Recent research into island biogeography has been performed on the basis of a variety of fauna and flora, including vascular plants, marine invertebrates, birds, and spiders(Kim et al., 2016). Through these floristic studies, new species such as Melampyrum koreanum K.-J. Kim & S.-M. Yun, Paraphlomis koreana S. C. Ko & G. Y. Chung, and Potentilla gageodoensis M. Kim were discovered and several species including Ajuga nipponensis Makino, Fimbristylis hookeriana Boeck., Carex tsushimensis (Ohwi) Ohwi, and Rhododendron keiskei var. hypoglaucum Suto & Suzuki were recorded for the first time in Korea (Kim and Yun, 2012; Kim and Kim, 2013; Kim et al., 2013; Ko et al., 2014; Nam et al., 2014; So et al., 2014; Yang et al., 2015). These findings are presumed to be due to the fact that the islands on the southwestern coast acts as a shelter or new frontier for some species due to geographical, climatic, and geographical conditions different from those in inland areas (National Institute of Biological Resources, 2015). Southwestern coastal islands of the Korean Peninsula, on the other hand, are the most favorable sites for ecological studies of distribution shift of evergreen trees because they are located at the northern limits of the species. Without surveys of exact floral diversity, numerous inhabited and uninhabited islands of west coast show symptoms of unnatural degradation or disappearance of rare species due to human disturbance and damage. Of islands of the Gogunsan Archipelago, the current study is focused on flora of Sinsi-do and Yami-do that were connected to the land by the Saemangeum Seawall, and flora of their adjacent islands such as Seonyu-do, Munyeo-do, Bian-do, and Duri-do (Fig. 1).

Fig. 1. A map of investigated area in the Gogunsan Archipelago.

The first study on the Gogunsan Archipelago was conducted by Lee et al. (1980), and they reported that the islands comprise 364 taxa in 85 families and 246 genera:355 species, five varieties, and five hybrids. Since then, studies have been carried out by Lee and Kim (1980), Kim(2008), Jang et al.(2013). The previous research has been carried out in limited areas, so a comprehensive survey of vascular plants in the region is needed. Accordingly, this study was conducted to secure voucher specimens through field surveys, create a detailed plant diversity list, and conservation strategies to ensure biodiversity and effective management are discussed in detail.

Materials and Methods

Survey site

The Gogunsan Archipelago is about 50 km from Gunsan-si, consisting of Sinsi-do, Seonyu-do, Munyeo-do, Yami-do, Bian-do, Duri-do, Daejang-do, Jangja-do, and many other uninhabited islands. The Gogunsan Archipelag is considered part of Okdo-myeon, Gunsan-si, Jeollabuk-do Province (126°15ʹ-126°30ʹ East longitude, 35°45ʹ-35°55ʹ North latitude), in Korea.

The geology of the Gogunsan Archipelago consists of the Jurrasic sedimentary rocks of Daedong system, Cretaceous sedimentary rocks of the Gyeongsang system, Late Cretaceous to early tertiary acidic volcanic rocks, and Quaternary sediments(Won and Song, 1980).

This study investigated six islands of the Gogunsan Archipelago: Sinsi-do, Seonyu-do, Munyeo-do, Yamido, Bian-do, and Duri-do. These islands, are affected by northwestern winds in the winter and are hot and rainy in the summer. Mean annual rainfall recorded at the weather station in the Gogunsan Archipelago is 1,284.5 mm and the mean annual temperature over last five years (2011- 2015) is 12.6°C with maximum temperature of 35°C and minimum of -11.3°C(Gunsan-si, 2017).

Survey method and analysis

The six islands were surveyed five times between March and October of 2016 for the investigation of the flora of vascular plants (Fig. 1, Table 1). The collected plants were made into the immersion and dried specimens. All the voucher specimens are deposited at the herbarium (KB) of the National Institute of Biological Resources in Korea. Various ecological habitats include mountain, flatland, wetland, valley, reclaimed land, sandy coast, mud flat, rocky roast, and abandoned salt field. Specimens were identified with the use of illustrations, photographs, and published descriptions(Lee, 1980; 2003; Lee, 1996; Lee, 2006; Park, 2009; Kim and Kim, 2011; Lee and Lee, 2015; Cho et al., 2016). The voucher specimens were listed according to the Cronquist classification system of vascular plants (Cronquist, 1981). Under each family, genera and species are listed in an alphabetical order. Korean and scientific names of vascular plants followed Lee et al. (2011) and a cultivated plant was indicated by (C) after the Korean name. The survey plants were also categorized based on endemic plants of the Korean Peninsula (Chung et al., 2017), red list plants(National Institute of Biological Resources, 2012), floristic regional indicator plants (National Institute of Environmental Research, 2012), and invasive alien plants(Jung et al., 2016). The habitat affinity types of species were categorized according to preference of habitat: forest, farmland, wetland, seacoast, and bare ground. We used cluster analysis to similarity of species composition among the the six islands. The index of similarity was analyzed using UPGMA (Unweighted Pair Group Method using Arithmetic algorithm) of MVSP(Multi Variate Statistical Package 3.1-Kovaok Computing Services), depicted as a dendrogram.

Table 1. The dates and site of vascular plants surveyed in the Gogunsan Archipelago.

Results and Discussion

Flora of vascular plants

From the five trips to the Gogunsan Archipelago, we identified 575 total taxa (527 species, five subspecies, 42 varieties, and one hybrid) categorized into included 118 families and 358 genera (Table 2, Appendix 1). The total number of voucher specimens was 2,847, which included some planted or cultivated plants. Of the 575 taxa investigated, pteridophyta included 17 taxa (16 species and one variety) belonging to 11 families and 14 genera, while gymnospermae included four taxa (4 species) belonging to two families and two genera, and angiospermae included 554 taxa, with 383 taxa (353 species, two subspecies, 27 varieties, and one hybrid) belonging to dicotyledoneae (88 families, 247 genera), and 14 taxa (154 species, three subspecies, and 14 varieties) belonging to monocotyledoneae (17 families, 95 genera). The 575 taxa of vascular plants in the flora of the Gogunsan Archipelago represented 13.2% of the total flora of Korea, 4,338 taxa (Lee et al., 2011).

Table 2. The number of vascular plants surveyed in the Gogunsan Archipelago.

Several species reported in previous studies could not be found in these surveys. Some of the major taxa missing are Selaginella involvens(Sw.) Spring, Pyrrosia hastata (Thunb. ex Houtt.) Ching, Corylus sieboldiana var. mandshurica (Maxim. & Rupr.) C. K. Schneid. Corispermum chinganicum Iljin, Machilus thunbergii Siebold & Zucc., Vicia bungei Ohwi, Cayratia japonica (Thunb.) Gagnep., Syringa reticulata var. mandshurica (Maxim.) H. Hara, Swertia japonica (Schult.) Griseb., Adenophora strica Miq., Taraxacum platycarpum Dahlst., Carex lenta D. Don, and Dioscorea japonica Thunb.. However, this study newly identified 162 taxa, such as Ophioglossum petiolatum Hook., Ceratophyllum demersum L., Morus tiliaefolia Makino (Fig. 2A), Rumex nipponicus Franch. & Sav., Rhodotypos scandens (Thunb.) Makino, Caesalpinia decapetala (Roth) Alston, Vigna minima (Roxb.) Ohwi & H. Ohashi, Zanthoxylum planispinum Siebold & Zucc., Oxalis dillenii Jacq., Adenophora polyantha Nakai, Carex maculata Boott (Fig. 2D), Rhynchospora faberi C. B. Clarke, and Phaenosperma globosa Munro & Benth.. It is assumed that the differences in the species lists are due to the difference of the survey sites and the investigation periods between the current and previous studies.

Fig. 2. Some remarkable taxa in the Gogunsan Archipelago. A. Morus tiliaefolia Makino.; B. Vaccinium bracteatum Thunb.; C. Carex ligulata var. austrokoreensis Ohwi; D. Carex maculata Boott; E. Carex phacota Spreng.; F. Chloris virgata Sw.; G. Parapholis incurve (L.) C. E. Hubb.; H. Lycoris flavescens M. Y. Kim & S. T. Lee; I. Iris rossii var. latifolia J. K. Sim & Y. S. Kim.

Korean endemic plants

According to a checklist of endemic plants on the Korean Peninsula (Chung et al., 2017), four endemic taxa were found in survey sites(Table 3): Clematis brachyura Maxim., Hemerocallis hakuunensis Nakai, Lycoris flavescens M. Y. Kim & S. T. Lee (Fig. 2H), and Iris rossii var. latifolia J. K. Sim & Y. S. Kim(Fig. 2I). The distribution patterns of these plants are different in that C. brachyura Maxim., H. hakuunensis Nakai, and I. rossii var. latifolia J. K. Sim & Y. S. Kim were discontinuously distributed in the ridges, while L. flavescens M. Y. Kim & S. T. Lee was found in lowland and sunny sides of a reservoir. Meanwhile, Rubus parvifolius var. taquetii(H. Lév.) Lauener & D. K. Ferguson is known synonym of R. parvifolius L.(Iwatsuki et al., 2001; Chung et al., 2017).

Table 3. The list of endemic plants surveyed in the Gogunsan Archipelago.

Red List plants

Of the Red List plants according to International Union for Conservation of Nature (IUCN), six of the species discovered in our surveys were evaluated. One species was categorized as Near Threatened (NT)[Pogonia minor (Makino) Makino], two species [Phacelurus latifolius (Steud.) Ohwi and Cymbidium goeringii(Rchb. f.) Rchb. f.] as Least Concern (LC), and three species as Not Evaluated (NE)(Polygonum polyneuron Franch. & Sav., Lithospermum arvense L. and Carex ligulata var. austrokoreensis Ohwi)(Table 4). Of these species, the small number of P. minor(Makino) Makino and C. ligulata var. austrokoreensis Ohwi were observed on the sunny forest edge in Munyeo-do and west valley in Sinsi-do, respectively.

Table 4. The list of red list plants surveyed in the Gogunsan Archipelago.

^aGrade: NT. Threatened species; LC. Least Concern species; NE. Not Evaluate species.

Floristic regional indicator plants

The floristic regional indicator plants found were 67 taxa comprising four taxa of the fourth grade included P. polyneuron Franch. & Sav., Ligustrum quihoui var. latifolium Nakai, C. ligulata var. austrokoreensis Ohwi, and L. flavescens M. Y. Kim & S. T. Lee. Fourteen taxa of the third grade included Vaccinium bracteatum Thunb. (Fig. 2B), Carex phacota Spreng. (Fig. 2E), Aletris spicata (Thunb.) Franch.. Lastly, 10 taxa of second grade included Stauntonia hexaphylla Decne., Caesalpinia decapetala (Roth) Alston, and Ainsliaea apiculata Sch. Bip. ex Zoll., and 39 taxa of first grade included Dicranopteris linearis (Burm. f.) Underw., Kadsura japonica (L.) Dunal, and Ruppia maritima L.. The complete ist is found in Table 5. These species account for 11.6% of vascular plants in the Gogunsan Archipelago. Of them, 18 taxa are floristic regional indicator plants over third grade, which indicates their relative importantce in biogeography (Table 5).

Table 5. The list of foristic regional indicator plants surveyed in the Gogunsan Archipelago.​​​​​​​

Table 5. Continued.​​​​​​​

Based on the flora of the Korean Peninsula, the Gogunsan Archipelago floristic division belongs to the southern province (Lee and Yim, 2002). The plants that are assumed to be at their northern limits on the Korean Peninsula are as follows: D. linearis (Burm. f.) Underw., Sinomenium acutum (Thunb.) Rehder & E. H. Wilson, V. bracteatum Thunb., L. quihoui var. latifolium Nakai, and C. ligulata var. austrokoreensis Ohwi (Lee and Lee, 2015; Korea National Arboretum, 2016).

Invasive alien plants

The 74 invasive alien plants(19 families, and 52 genera), based on Jung et al. (2016), include Oxalis dillenii Jacq., Aegilops cylindrica Host, Chloris virgata Sw.(Fig. 2F), and Parapholis incurve (L.) C. E. Hubb. (Fig. 2G), and Sorghum halepense (L.) Pers. (Table 6). The percent of naturalized index (NI) was 12.8% of the total 575 taxa vascular plants. Six taxa are considered ecosystem disturbance plants: Rumex acetosella L., Ambrosia artemisiifolia L., Aster pilosus Willd., Hypochaeris radicata (Thunb.) Franch. & Sav., Lactuca scariola L., and Solidago altissima (Aiton) McNeill. Meanwhile, seven taxa are archaeophyte [Amaranthus lividus L., Fagopyrum esculentum Moench, Abutilon theophrasti Medik., Brassica juncea (L.) Czern., Thlaspi arvense L., Lycium chinense Mill., and Eclipta prostrata (L.) L.], while two species are considered alien species that were introduced intentionally and but are highly likely to spread in the natural ecosystem(Ainus firma Siebold & Zucc., and Indigofera bungeana Walp.). The invasive alien plants in the Gogunsan Aarchipelgo were frequently observed around marine landing places of Seonyu-do, Bian-do, and Durido. Some species were also found around rest areas, road cracks, beaches, and farmlands on Sinsi-do and Yami-do island. Due to their location near human-modified habitats, we hypothesize that this inflow of alien species is caused by constant interference in plant diversity on the island by human activities. In the past these islands(Sunyu-do, Munyeo-do, Bian-do, and Duri-do) were only accessible by crossing the sea, but the number of visitors is expected to increase due to the opening of a bridge in December 2017. Accordingly, it is necessary to set up an effective plan to mimize the introducing invasive alien plants, including monitoring the distribution of alien species and rooting out regularly.

Table 6. The list of invasive alien plants surveyed in the Gogunsan Archipelago.​​​​​​​

Table 6. Continued.​​​​​​​

Species richness and classification of habitat affinity types

Species richness was highest in Sinsi-do (342 taxa, 89 families and 234 genera), followed by Bian-do (263 taxa, 91 families and 211 genera), Seonyu-do (252 taxa, 72 families and 190 genera), Munyeo-do (201 taxa, 76 families and 167 genera), Yami-do (184 taxa, 72 families and 151 genera), and Duri-do (68 taxa, 39 families and 61 genera) (Table 2). According to the theory of island biogeography, larger islands and closer islands to the mainland should have more species (MacArthur and Wilson, 1967), and this phenomenon is supported in the current flora study. Ranking of species richness shows close relationships with the size of the island. The area of each island is as follows: Sinsi-do (4.25 km² ), Seonyu-do (2.13 km² ), Munyeo-do (1.74 km² ), Bian-do (1.63 km² ), Yamido (0.41 km² ), and Duri-do (0.14 km² )(Gunsan-si, 2017).

For the result of analyzing habitat affinity types for total vascular plants(Fig. 3), the proportion of forest species was the highest on all islands. Following forest habitats, the most common types on most of the islands were farmland, seacoast, bare ground. This result is likely caused by the size of each land mosaic (types of ecosystem). In other words, it is that species richness is higher as the size of land mosaic is larger. The spatial elements, heterogeneity, and diversity of a landscape reflect a natural system, including disturbances and human influences on some areas(Turner and Bratton, 1987; Hong, 1998). The animals and plants survive by using habitat of spatially heterogeneous landscape. Therefore, structural diversity and size of land mosaic within the landscape is closely related with species richness and ecosystem quality (Peterken et al., 1992; Forman and Collinge, 1996; Hong et al., 2000; Kurki et al., 2000). If the islands are exposed to rapid environmental changes, it is more likely that existing flora will be replaced sooner than anywhere else by new species because the islands are small and isolated. Therefore, it is important to investigate and analyze flora of the islands in order to protect existing flora. Also, these results can be used as a baseline data to conserve and establish management plan of the islands (Kim et al., 2016).

Fig. 3. Variations of percentage of habitat affinity types in the GogunsanArchipelago.

Similarity analysis

As the result of a similarity analysis based on total vascular plants, the similarity between Seonyu-do and Sinsi-do (node 1) was the highest at 53.2%. The index was lower in the following order: Munye-do and node 1 51.6% (node 2), node 2 and Bian-do 46.7% (node 3), node 3 and Yami-do 42.7% (node 4), and node 4 and Duri-do 22.2% (Fig. 4). Meanwhile, as the result of a similarity analysis excluding invasive alien and ruderal plants, the similarity between Sinsi-do and Munye-do (node 1) was the highest at 54.5%. The index was lower in the following order: Seonyu-do and node 1 54.2% (node 2), node 2 and Biando 46.3% (node 3), node 3 and Yami-do 42.8% (node 4), and node 4 and Duri-do 22.6% (Fig. 5). The index of similarity based on the analysis excluding invasive alien and ruderal plants was higher than when all species were included. The index of similarity between the adjacent islands also was higher. This means that the proportion of invasive alien plants and ruderal plants increase with increasing disturbance by human activity. As the proportion of these species increase by human activity, each island does not have unique, local diversity. Artificial disturbance also is closely related with invasive alien species richness and composition of the islands(Chung and Hong, 2006). If the natural vegetation is temporarily destroyed by invasion and spread of invasive alien plants, the natural ecosystem will be disrupted and the rare or endemic plants will become extinct. Therefore these data can be used to conserve ecosystem of the islands and control invasive alien plants. Furthermore, it is essential to do continuous, long-term surveys monitoring environmental and flora changes (Chung and Hong, 2006; Kim et al., 2016).

Fig. 4. Dendrograms showing the degree of Sørensen similarity based on vascular fora data of the Gogunsan Archipelago.

Fig. 5. Dendrograms showing the degree of Sørensen similarity based on native flora data (except invasive alien plants, ruderal plants) of the Gogunsan Archipelago.