Wetlands provide various habitats for organisms and are ecologically beneficial for mitigating floods, water pollution, and global warming by storing nitrogen and carbon dioxide (Mitsch and Gosselink 2000). Thus, wetlands are considered one of the most valuable ecosystems on Earth (Lee 2000). As recognition for their ecological value has grown, wetland restoration is being conducted Wetlands provide various habitats for organisms and are ecologically beneficial for mitigating floods, water pollution, and global warming by storing nitrogen and carbon dioxide (Mitsch and Gosselink 2000). Thus, wetlands are considered one of the most valuable ecosystems on Earth (Lee 2000). As recognition for their ecological value has grown, wetland restoration is being conducted actively. In particular, abandoned paddy fields are useful as wetlands in an ecological context, because rice fields themselves are one of the most important wetlands and are widely distributed in Korea.
Although total farmland area has sharply decreased since 1995, the area of abandoned paddy fields has increased(Ministry of Agriculture and Forestry in Korea mea2004), and abandoned paddy fields face secondary succession. Abandoned paddy fields have high plant diversity and contain various habitats for fish, amphibians, and reptiles. They also perform an aesthetic function; thus, becoming recognized as important wetlands (Koo 2003). Abandoned paddy fields at the early successional stage serve as habitat for
Despite its ecological importance, usefulness, and previous
Eight wetlands in South Korea that were dominated by rush were selected (Fig. 1). The average annual temperatures were 13.0, 12.2, and 12.8°C for Seoul (Fig. 2a), Wonju (Fig. 2b), and Namwon (Fig. 2c), respectively, whereas annual precipitation was 140.2, 130.0, and 115.1 mm, respectively (Fig. 2). Most of the studied wetlands were abandoned paddy fields aged 3-10 years. Rainfall and ground water were the main water sources at the study sites. The highest water level was set at 20-30 cm by small banks during the wet season.
We studied vegetation during the driest growing period in Korea (May 27-June 16, 2006). We established 63 randomly distributed 1 m × 1 m quadrats in
Water samples were collected at each quadrat. Water depth (WD) was defined as the distance from the water table to the soil surface; it was positive when the soil surface was below the water table and negative when the soil surface was above the water table. Water temperature and turbidity (TUR) were measured with a thermocouple thermometer (Center 300; Center Technology Co., Shu-Lin, Taiwan) and turbidimeter (Hach 2110P; Hach Co., Loveland, CO, USA), respectively. Dissolved oxygen, conductivity (CON), and total dissolved solid (TDS) were measured using a Corning Checkmate II (model 311; Corning, Lowell, MA, USA), and pH was measured using a pH meter (model AP 63; Fisher, Pittsburgh, PA, USA) in the field. Water samples were collected at each site and filtered with a membrane filter (pore size, 0.45 ㎛). The nutrients in the water samples were analyzed in the laboratory. NO3-N, NH4-N, and PO4-P were analyzed by the hydrazine method (Kamphake et al. 1967), indo-phenol method (Murphy and Riley 1962), and ascorbic acid reduction method (Solorzano 1969), respectively. Cation contents such as K+, Ca2+, Na+, and Mg2+ were mea-
[Fig. 1.] Study areas. 1 Incheon Gangwha-gun Gyodong-do; 2 Incheon Gangwha-gun Yangdo-myeon Dojang-ri; 3 Incheon Gangwha-gun Gilsang-myeon Giljick-ri; 4 Gyeonggi-do Hwaseong Jungnam-myeon; 5 Gyeonggi-do Gangju Docheok-myeon Nogok-ri;6 Gangwon-do Wonju guile-ri; 7 Jeolla-nam-do Gokseong Singi-ri;8 Jeollanam-do Gokseong Wolbong-ri.
sured with an atomic absorption spectrometer (model AA240FS; Varianm Palo Alto, CA, USA).
Soil was collected at a depth of 0-5 cm from the surface at each quadrat using a soil hand auger. Gravel and large organic debris were removed from the samples, and they were passed through a 2 mm sive (standard sieve #10). Soil texture was determined using the hydrometer analysis method and a texture triangle (Sheldrick and Wang 1993). Organic matter content was analyzed by the loss-on ignition method (LOI) (Boyle 2004). Soil moisture was measured as fresh water moisture, which considers the total amount of water in the sample and as air-dry moisture, and reveals soil particle moisture in the sample (Topp 1993).
Soil solutions were prepared by mixing the soil samples with distilled water at a mass ratio of 1 to 5, and pH, CON, and TDS were measured. NO3-N and NH4-N were extracted with 2 M KCI solutions (Km et al. 2004) and measured colorimetrically using the hydrazine and in dophenol methods, respectively (Murphy and Riley 1962, Kamphake et al. 1967). PO4-P was extracted with Bray No. 1 solution (Bray and Kurtz 1945) and measured colorimetrically using the ascorbic acid reduction method (Solorzano 1969). Total carbon (T-C), total hydrogen (T-H), and total nitrogen (T-N) were determined with an elemental analyzer (model EA1110; CE Instruments, Wigan,UK) at th National Center for Inter-University Research Facilities, Seoul National University. K+, Ca2+, Na+, and Mg2+ were extracted with N ammonium acetate solution (Allen et al. 1974) and measured with an atomic absorption spectrometer (model AA240FS; Varian).
We calculated importance values (I.V.), occurrence frequency (Occ.), and the diversity index (H’) for the vegetation data in each quadrat (Shannon and Weaver 1949, Kim et al. 2004):
To determine the optimal environment for the growth and distribution of
Fifty-three plant species from 28 families were found in the
The water regime is a major determinant of plant community development and patterns in wetlands (Kwon et al. 2007). Flooding primarily determines plant distribution and can affect species richness and diversity (Huston 1994, Ferreira and Stohlgren 1999, Stromberg 2001, Riis and Hawes 2002). Additionally, WD affects light transmission as well as chemical changes in sediment and water TUR; thus, becoming a significant environmental factor in the growth of wetland plants (Grace and Wetzel 1981, Spence 1982).
The highest water level in which
[Fig. 3.] Juncus effusus distribution patterns according to water characteristics: (a) water depth (b) dissolved oxygen (DO) (c) conductivity (CON) (d) total dissolved solid (TDS) (e) pH (f) K+ (g) Ca2+ (h) Na+ (i) Mg2+ (j) NO3--N (k) NH4+-N and (l) PO42--P. The circles on the line represent the sample distribution (quadrat locations) on the gradient of corresponding environmental factors. The box on the line shows the optimal range for distribution of each corresponding environmental variable. Density (individuals/m2) cover (%) importance values (I.V.) importance value (%) and height (cm) the average height of J. effusus.
[Table 1.] Total environmental range of distribution (TRD) and optimal environmental range of distribution (ORD) for the physicochemical characteristics of the environment in which Juncus effusus were distributed and a comparison with the ORDs of Zizania latifolia (Kwon et al. 2006) Typha angustifolia (Kwon et al. 2006) Scirpus tabernaemontani (Lee et al. 2007) and Typha orientalis (Lee et al. 2007)
[Fig. 4.] Distribution patterns of Juncus effusus according to soil characteristics: (a) soil texture (b) fresh moisture (c) air-dry moisture (d) loss-on ignition (e) conductivity (f) pH (g) extracted (E)K (h) ECa (i) ENa (j) EMg (k) NO3--N (l) NH4+-N (m) PO42--P (n) total-nitrogen (o) total-carbon and (p) total-hydrogen. The circles on the line represent the sample distribution (quadrat locations) on the gradient of corresponding environmental factors. The box on the line shows the optimal range for distribution of each corresponding environmental variable. Density (individuals/m2) cover (%) importance values (I.V.) importance value (%) and height (cm) the average height of J. effusus.
Physicochemical environments in a body of water can influence wetland plants. The ORD of Con, TDS, and cations including K+, Ca2+, Na+, and Mg2+ in
Soil variables are also important when determining plant community composition (Fitter 1982, Keddy 1984, Kwon et al. 2007). Although soil variables may be more important when determining spatial variations in plant community composition and structure, the lack of soil variable data influencing plant distribution makes it almost impossible to evaluate these relationships at present (Kwon et al. 2007). In particular, the vegetation dynamics of many plant communities are thought to be strongly influenced by soil nutrient heterogeneity, but few experimental studies have investigated this relationship. Sixty soil environment characteristics of the TRDs and ORDs of
Soil texture is a major determinant in the distribution and structure of wetland plants (Collins et al. 1987). Absorbing water and nutrients in clay soils is difficult for plants due to the strong adherence of water to clay particles (Robinson 1951, Troeh and Thompson 1993). Besides, high clay content causes high water TUR, obstructing the distribution of submerged plants (Kim 2003). In contrast, high sand content in the planting foundation of emergent plants causes a lack of nutrients, followed by limited growth (Kim 2003). Therefore, determining the appropriate soil texture is key to the growth of wetland plants. The soil texture in the
Soil moisture and organic matter are also significant factors that could determine plant distribution and vegetation structure in wetlands. Organic matter plays an important role in nutrient cycling and retention, because nutrients absorbed by wetland plants can be released by the mineralization and decomposition of organic matter submerged as litter (Mitsch and Gosselink 2000). However, an excess accumulation of organic matter may influence aquatic plant productivity and competition and, thus, moderate organic matter content is important for survival of any aquatic plant (Kwon et al. 2007). In numerous studies, seed density increases with soil moisture due to the presence of high
The eK, eCa, eNa, and eMg in the
2--P was 0.491-11.552 mg/kg with a
2) The optimal WD in the
3) The soil texture ORD included loam, silty loam, and sandy loam.
4) The ORD for fresh moisture was from 30.17% to 49.06%. The ORD for air-dry moisture was 1.05-2.96%, and that for LOI was 5.07-7.81%. Organic matter was relatively lower in content than that for other species, but the introduced
5) The water and soil physicochemical environments clearly showed a different distribution than other emergent plants, including