During the past century, approximately fifty percent of the world’s wetlands have been destroyed, largely as a result of human activities (UNWWAP, 2003; Fraser & Keddy, 2005). An increased human population coupled with habitat loss and fragmentation has led to shrinkage of wetland areas, and data show that as they decrease, their key functions decline (Fraser & Keddy, 2005). Reduced wetland area does not only cause more flooding in spring, less available water during drought, greater risk of water pollution, less food production, and reduced carbon storage, but also leads to the loss of habitats for many animals and plants and the loss of wetland’s capacity for regulating the regional climate (MEA, 2005; Ramsar, 2011). Much of the remaining pristine wetland systems are found in the world’s largest wetlands, and yet these areas have been subjected to surprisingly little scientific research (Fraser & Keddy, 2005). Therefore, studying the floristic richness and composition of a given wetland is essential when a major human impact is expected to take place, especially if it is known that endemic and threatened plants are present. Such a study is a mandatory preliminary step in order to implement adequate conservation measures.

The middle reaches of the Yangtze River is an extensive network of rivers, shallow lakes and wetlands, and constitutes one of the main Asian hotspots of biodiversity (Olson & Dinerstein, 2002; Xie, 2003; Fang et al., 2006; López-Pujol & Ren, 2009). The huge human-driven transformation of this region (including intensive land reclamation and the construction of numerous dams and dikes) has altered most of the water network connections and, at present, the Poyang and Dongting lakes are the only sizable lakes that remain linked to the Yangtze River (Fang et al., 2006; Li, 2009; Finlayson et al., 2010). The considerable biodiversity in these big lakes is also under threat by dam construction (e.g. López-Pujol & Ren, 2009). Such is the case for Poyang Lake, the biggest freshwater lake in China.

Poyang Lake is located at the south bank of the middle reaches of the Yangtze River, the largest river in China. This lake constitutes one of the six largest wetlands in China, with a maximum area of up to 4125 km² and a highest water depth of 20 m (Li, 2009; Finlayson et al., 2010). The ecological importance of the lake and the associated wetland has been recognized at both national and international levels; in 1983 the Poyang Lake National Nature Reserve was established, and in 1992 it was listed as a Ramsar site (www.ramsar.org/). However, the local government has proposed to build a big dam at the northern end of Poyang Lake, 27 km from the Yangtze River (Li, 2009). The main purpose of this planned dam is to stabilize the lake’s water level. During the last decade (and especially during 2011; Xinhua, 2011; China Daily, 2012; Feng et al., 2012), large sections of the lake have dried up; in January 2012, the inundation area dropped below 200 km² (China Daily, 2012), which is less than 5% of its maximum extension. This drought produced losses in fisheries and other industries (Li, 2009; People’s Daily 2011; China Daily, 2012). However, disrupting the seasonal water flow by damming would also likely have severe negative impacts on the local climate and biodiversity (Li, 2009; Harris & Hao, 2010), and thus the central government has suspended the project pending further studies.

The aim of this study is two-fold: (1) to survey the floristic richness of the whole region of Poyang Lake, by cataloguing both plant species and the dominant community types; and (2) to provide recommendations for the protection of plant diversity prior to the building of the dam based on our data gathering and analysis.

Study area

Poyang Lake, while considered a shallow lake, does have flowing water and is the catchment for most of the surface water pooling in Jiangxi Province (CPLRE, 1988). The lake also functions in sediment transport (from the rivers flowing into the lake to the Yangtze River), and serves as a water accumulation center. The lake is located in a very flat area (the Middle-Lower Yangtze Plain) characterized by a mild subtropical monsoon climate. The water level of Poyang Lake is mainly influenced by the local watershed as well as by the Yangtze River’s water level. Inter-year and annual water level variation changes dramatically, with the inter-annual maximum amplitude reaching 16.69 m, which is mainly driven by the local precipitation regime and water level of Yangtze main channel (Feng et al., 2012). Its flood season is from April to September, and its dry season is from October to the following March. The lake area differs substantially between flood season and dry season: its maximum area is up to 22 times that of the minimum area (Liu et al., 2006). On average, the lake has a surface of over 3000 km² in the rainy season and less than 1000 km² in the dry season (Feng et al., 2011).

Sampling site selection

Based on Poyang Lake’s geographical features, we selected nine areas (Table 1) within its wetland to conduct surveys of both plant species and community types. We used the broad definition provided by the Ramsar Convention to define the wetland; namely, wetlands are not only the areas permanently or temporarily covered by water (wetlands in the strict sense), but also the coastal or riparian zones adjacent to wetlands (RCS, 2013). The nine selected areas were the following: (1) Ganjiang River bank near Nanchang Bridge, (2) Taizi River of Hongwei Village in Nanji Mountain, (3) west branch of Ganjiang River in Wucheng Town of Yongxiu County, (4) Old petrochemical wharf in Xingzi County, (5) Shizhong Mountain in Hukou County, (6) Changjiang in Poyang County, (7) East River of Xinjiang River, (8) Sub-river of Chenjia Lake, and (9) Sanyang Bridge of Fuhe River (Fig. 1 and Table 1). In the above nine areas, we selected a number of sampling sites according to the shape and size of the local water bodies. Sites were randomly located along a transect from the central core of the wetland to its edge. Additional sampling sites were selected both in areas with very large wetlands and in cases where we detected that the distribution of plant species was uneven (Table 1). We set at least three plots (of 1 × 1 m) at each of the sampling sites. In total, 317 sampling plots were established, which were representative of three main habitats or ecological zones of the Poyang Lake wetland system: permanent aquatic areas, seasonally aquatic areas (that is, those covered during the flood season, e.g. lakeshore areas), and areas adjacent to wetlands (i.e. those areas only flooded occasionally) (Table 1).

Table 1.

Plant species and plant community measures

For each plot, we catalogued all the plant taxa occurring there; plants were identified following Moss Flora of China (MFCEC, 1999–2011), Flora of China (http://flora.huh.harvard.edu/china/), and Flora of Jiangxi (ECFJ, 1993). We also recorded the dominant plant community types for each plot, which were identified following the criteria of Vegetation of China (Wu, 1980). For each plant taxon, a series of characteristics useful for recognizing the plant community types and defining their features (community structure, composition) were determined, including: habit (annual, biennial, or perennial), life-form (herb, shrub, tree, or vine), origin (see below), hydro-ecotype (see below), coverage, height, phenology, and abundance. Some of these traits were determined with the aid of the Higher aquatic plants in Jiangxi Province (Guan & Zhang, 1989) and other relevant sources (e.g. Flora of China; http://flora.huh.harvard.edu/china/). For the origin, we assigned each taxon to one of the following categories: endemic to China, native to China, and alien; the alien taxa, in turn were classified in three groups: naturalized, invasive, and cultivated. The hydro-ecotypes of the identified plant species were determined depending on their water requirements: plant species that grow in moist environments and that cannot endure long term water deficiency were regarded as hygrophytes, those that grow in moderately moist habitats as mesophytes, those that grow in arid environments and show drought tolerance as xerophytes, and those truly aquatic as hydrophytes (Li et al., 2004).

All the fieldwork was conducted in October 2011. In addition, several relevant works (i.e. Guan & Zhang, 1989; Ge & Wu, 2006; JPLNNRA, 2008; Ge et al., 2010; Hu et al., 2010; Wu et al., 2010a ; Li et al., 2011) were also consulted to complete the list of plant species and communities occurring within the Poyang Lake wetland. Infraspecific taxa (i.e. subspecies, varieties, and forms) were treated as equivalent to species to simplify the analyses.

Species richness

Poyang Lake harbored a high diversity of plants: up to 124 families, 339 genera, and 512 species (including sub-species, varieties and forms) were found in the study area (see Appendix). The number of species belonging to bryophyta, pteridophyta, gymnospermae, and angiospermae was two, 16, 13, and 481, respectively, which accounted for 0.4%, 3.1%, 2.5%, and 93.9% of all species, respectively. Of the angiosperms, eight were basal angiosperms, 123 were monocots, and 350 were eudicots. The plant families with the greatest number of species were Asteraceae (38 species), Poaceae (35), Cyperaceae (25), and Fabaceae (24). These, together with other six families (Fig. 2), contained a total of 208 species, which accounted for 40.6% of all plant species. Polygonum L., Carex L., and Potamogeton L. were the genera with the largest number of representatives in the wetland, with 10, nine, and seven species, respectively.

The habits and life-forms of all plant species in the Poyang Lake wetland were also diverse. Most of the species recorded in the wetland were herbs (371 out of 512 species), although these greatly differed regarding the habit (Fig. 3). Shrubs represented about 11.3% of the total number of species (58 species), trees about 13.3% (68 species), and vines ca. 2.9% (15 species) (Fig. 3). Regarding the hydro-ecotype, the bulk of the plants in the wetland were mesophytes, which accounted for up to 62.7% of the total number of species (321 species); moreover, plants that were either classifed as mesophytes or hygrophytes represented 13.7%, those that were either mesophytes or xerophytes represented 9.8%, and those that were either mesophytes, xerophytes, or hygrophytes accounted for 0.4%. Species with strict water requirements constituted a relatively low percentage of the Poyang wetland plants: hydrophytes acounted for 7.0%, hygrophytes for 3.7%, and those species that were either classified as hydrophytes or hygrophytes, for 2.7%.

As for the origin, most of the plant taxa that occur in the Poyang Lake wetland were native to China (402 taxa, 78.5%), whereas only 31 (6.1%) were endemic to China. Among the endemics, there were several rare, threatened, and/or nationally protected species; some outstanding examples include (1) the fern Isoëtes sinensis Palmer (which is ‘critically endangered’ according to IUCN criteria, and included both in the National List of Rare and Endangered Plant Species of 1984 and in the Catalogue of the National Protected Key Wild Plants of 1999), as well as (2) the gymosperms Ginkgo biloba L. and Metasequoia glyptostroboides Hu & W. C. Cheng (which are ‘endangered’ and included in both protection lists). A total of 79 species of the 512 recorded within the wetland (that is, 15.4%) were of alien origin; of these, 25 were cultivated, 31 were invasive, 11 were naturalized, and 12 were of uncertain nature, which accounted for 4.9%, 6.1%, 2.1%, and 2.3% of all species, respectively. Although not very large, we found some differences regarding the origin of plant taxa between ecological zones (Fig. 4): the percentage of native taxa decreases from permanent aquatic areas to areas adjacent to wetlands, whereas the reverse trend was observed for the alien plants.

Plant communities

Based on the species composition in the Poyang Lake wetlands, eight dominant plant communities can be distinguished:

Floristic and vegetation features of Poyang Lake

The vegetation resources in Jiangxi Province are abundant, possessing a high taxonomic richness along with numerous and complex vegetation types that are closely related to the floristic origin and evolution of this region (ECFJ, 1993; Wang, 2004; Peng, 2007; Hu et al., 2010). The regional vegetation of Jiangxi Province belongs to subtropical evergreen broad-leaved forest, with some warm temperate plant elements (deciduous broad-leaved forest) that are mixed gradually in the northern part of the Poyang Lake wetland (i.e. in the northern part of Jiangxi Province) (Wu, 1980; Hou, 1983). The vegetation of the province can be regarded as unique in the sense that there are many subtropical endemic genera, relic plant species, and ancient tropical flora elements (ECFJ, 1993); in fact, the province harbour some of the main centres of plant endemism in China (López-Pujol et al., 2011; Huang et al., 2012). Our study confirms that these features (high species richness, endemism and presence of relict elements) also characterize the flora of Poyang Lake.

The Poyang Lake wetland is very rich in terms of total plant species, and harbours a significant part of the total flora of the province. Of the 49 families, 114 genera, and 400 species of ferns recorded in Jiangxi Province (ECFJ, 1993), 12 families, 13 genera and 16 species have been identified in the present study (which accounts for 22.5%, 11.4%, and 4%, respectively). Regarding gymnosperms, the provincial flora contains eight families, 23 genera and 30 gymnosperm species (ECFJ, 1993); in the Poyang Lake wetland, five families, 10 genera and 13 species are found, accounting for 62.5%, 43.5%, and 43.3%, respectively. The wetland flora is also rich in angiosperms: of the 220 families, 1309 genera, and 2373 species included in Flora of Jiangxi (Guan & Zhang, 1989; ECFJ, 1993), we have found 106 families, 314 genera, and 481 species, which accounts for 48.2%, 24.0%, and 20.3%, respectively. The large number of plant taxa identified in the present study (512) is in agreement with recent studies (Ge & Wu, 2006; JPLNNRA, 2008; Jiang et al., 2009; see Table 3), although our work is the first covering all the wetlands range and all the major plant communities in Poyang Lake.

As mentioned, many endemic (up to 38 species, 7.4% of the total) and relict floristic elements are present in Poyang Lake. For example, we found Cryptomeria japonica (Thunb. ex L. f.) D. Don var. sinensis Miq., a conifer lineage that might date from the Cretaceous according to molecular data (Ran et al., 2010). At present, only a single species with two varieties exists in the world; one is native to Japan [i.e. Cryptomeria japonica (Thunb. ex L. f.) D. Don var. japonica], and the other one (Cryptomeria japonica var. sinensis) is widespread in China, including Jiangxi Province. Another relict species that occurs within the Poyang Lake wetland is Cunninghamia lanceolata (Lamb.) Hook., a companion species in the evergreen broad-leaved forest now widely cultivated as a plantation tree. It has become one of the most important and valuable fast-growing species in subtropical China. Metasequoia glyptostroboides and Ginkgo biloba are also relict species that have lineages likely dating from the Cretaceous (Ran et al., 2010). These rare and nationally protected species (Fu & Jin, 1992; YNCC, 2011) are widely found within the Poyang Lake wetland.

When Poyang Lake is at its normal water level (14 to 15 meters), the inundated area is over 3000 km² (Feng et al., 2011), which represents about 2% of the total land mass of Jiangxi Province. Because of the high plant diversity in this small area, it is of vital importance to ensure an adequate protection of Poyang Lake. Indeed, the wetland represents a regional hotspot of biodiversity and its species richness is higher than that of other wetlands within the Yangtze Basin. Poyang wetland alone harbours a very important part of China’s wetland flora: 65% of the gymnosperms (13 out of 20; An et al., 2007), and 40% of the angiosperms (481 out of 1200; An et al., 2007). For example, Dongting Lake, the second largest freshwater lake in China (and with a similar area to Poyang; Table 3), has considerably less plant diversity, with only about 192 plant species reported (ECWVC, 1999). Another sizable lake (Taihu Lake, which is located in the Yangtze Delta plain) also has a much lower plant species richness (74 species; Zhang et al., 1999), although for the Taihu Lake study only the permanent and seasonally aquatic areas were studied (Table 3).

Table 3

In addition to biogeographical and ecological reasons, the wealth of species in Poyang wetland may be partly due to its relatively good conservation status (Li, 2009). Mirroring this, most of the species present in the wetland are native (around 80%), a percentage that increases from areas adjacent to wetlands (the most disturbed due to their strong cultivation, especially rice) to permanent aquatic areas (the less disturbed ones; Fig. 4). On the contrary, the reverse trend occurs for the alien plants, which peak in the areas adjacent to wetlands. Human disturbances, such as fires, urbanization, or agricultural practices, may encourange invasions because new ecological niches are available for alien species (Mack et al. 2000, Simberloff & Rejmánek, 2011).

Up to 15 regional and non-regional vegetation types defined in the provincial flora (ECFJ, 1993) have been recorded in Jiangxi, of which four (meadows, aquatic plant communities, herb marshes and peat swamps) are present in the Poyang Lake wetland. In fact, Poyang Lake harbors a representative sample of the vegetation types reported for China as a whole (two of the 11 vegetation type groups, and 55 of the 960 formations and sub-formations; Zhang, 2007; Hu et al., 2010; Zhang et al., 2012). In our study, up to eight dominant plant community types have been identified in the Poyang Lake wetland, and these eight communities belong to the above four vegetation types. Cynodon dactylon communities, Carex spp. communities, and Polygonum criopolitanum communities belong to the meadow vegetation type; Phragmites australis – Miscanthus lutarioriparius communities belong to the herb marsh vegetation type; Nymphoides peltata – Potamogeton wrightii – Hydrilla verticillata + Vallisneria natans communities, Eleocharis valleculosa communities, and Vallisneria spp. communities belong to the aquatic plant vegetation type; and Phalaris arundinacea – Polygonum criopolitanum – Cardamine lyrata communities belong to the peat swamp vegetation type.

Conservation implications

If the reservoir is built with the purpose of stabilizing lake levels, the original habitats of many species will be permanently flooded: most of the mesophytes and hygrophytes that live in the currently seasonally flooded areas will lose their habitat. Flooding will have a severe impact on several rare and endangered plants, e.g. Cryptomeria japonica var. sinensis, Ginkgo biloba, and Metasequoia glyptostroboides. Hydrophytes will also be affected, as the water levels and flood regime of Poyang Lake will be deeply modified. Regarding the vegetation, Phragmites australis – Miscanthus lutarioriparius communities, and Cynodon dactylon communities would be among the most affected by the potential flooding because these occur on the shore. On the other hand, those communities that may survive at a very wide variety of hydrological conditions, such as Carex ssp. communities, would not be seriously affected; these Carex spp. communities, which are the dominant type in Poyang Lake wetland, can be found at depths ranging from 0 to nearly 15 m, with the percent time inundated between 0 and 100% (Zhang et al., 2012).

If the dam is constructed, water flow will be slower and the regime of water-level fluctuations will change in Poyang Lake and related rivers. These modifications can accelerate eutrophication and will likely facilitate clonal reproduction and spread of invasive plants (Mack et al., 2000), especially of the floating macrophytes such as the water hyacinth, Eichhornia crassipes (Mart.) Solms, and the water lettuce, Pistia stratiotes L., both of which were already found in Poyang Lake (see Appendix and Fig. 5). These two noxious plant invaders can seriously threaten the local plant diversity and ecosystem functioning (Barrett, 1989). Serious attention should be paid to these invasive plants and the other alien species that may likely cause similar environmental problems after the reservoir is built. Construction of the Three Gorges Dam, about 900 km usptream on the Yangtze River, have facilitated the establishment of highly invasive alien species in its reservoir region, including the above-mentioned Eichhornia crassipes, Alternanthera philoxeroides (Mart.) Griseb., or Erigeron sumatrensis Retz. (Ding et al., 2008). In this sense, appropriate management strategies to minimize further invasions in Poyang wetland, including setting up early detection methods and enforcing quarantines and inspection procedures, should be urgently implemented. Clearly, more specific research is needed (e.g. vegetation succession and biophysical and ecological modelling; Kummu et al., 2006) to precisely identify and quantify the possible impacts on the biodiversity that damming will exert.

Disappearance or disturbance of forests, shrublands, grasslands, and aquatic communities due to permanent flooding will lead to great ecological losses. Therefore, in order to minimize these impacts, it is imperative to set up a series of in situ conservation measures that might include enhancing nature reserves, restoring degraded ecosystems, and optimizing artificial ecosystems. Setting up new nature reserves and expanding existing ones seems an urgent and necessary task given that new pressures on Poyang wetland are arising, such as the massive sand dredging currently being undertaken in an effort to cope with the demand for sand used in construction (Harris & Hao, 2010). Constructed and restored wetlands, e.g. paddy fields and fishing grounds, often lack, however, the ecological functions provided by natural habitats (Zedler, 1993; Kentula, 1996) and thus additional research should be conducted in this direction. The ex situ conservation of the rare and interesting species affected by damming could be accomplished by transplanting these species into botanical gardens and keeping their seeds in germplasm banks. These measures, in addition to contributing to the plant diversity protection, would also serve for economic development.

Appendix