Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 3: Ecosystem Effects <strong>of</strong> Invasive SpartinaSPARTINA ALTERNIFLORA INVASIONS IN THE YANGTZE RIVER ESTUARY,CHINA:ASYNOPSISB. LI 1 ,C-Z.LIAO, X-D. ZHANG, H-L. CHEN,Q.WANG, Z-Y. CHEN, X-J. GAN, J-H. WU,B.ZHAO, Z-J. MA,X-L. CHENG,L-F.JIANG, Y-Q. LUO, AND J-K. CHENCoastal Ecosystems Research Station <strong>of</strong> <strong>the</strong> Yangtze River Estuary, Ministry <strong>of</strong> Education Key Laboratory for BiodiversityScience and Ecological Engineering, The Institute <strong>of</strong> Biodiversity Science, Fudan University, #220 Handan Road, Shanghai200433, China1 For correspondence: bool@fudan.edu.cnSpartina alterniflora was first found in <strong>the</strong> Yangtze River estuary in <strong>the</strong> mid 1990s, and has nowbecome <strong>the</strong> most abundant vascular plant in <strong>the</strong> estuarine marshlands. We have investigated <strong>the</strong>potential consequences <strong>of</strong> Spartina alterniflora invasions to <strong>the</strong> salt marshes on two large islands in<strong>the</strong> estuary, Chongming and Jiuduansha, over <strong>the</strong> past five years, focusing on effects on biodiversityand ecosystem processes <strong>of</strong> <strong>the</strong> marshlands resulting from <strong>the</strong> invasion. We here summarize <strong>the</strong>major findings from our previous work and provide <strong>the</strong> relevant literature.Keywords: Biodiversity, ecosystem processes, plant invasions, saltmarshes, Spartina alterniflora,Yangtze River estuaryINTRODUCTIONThe Yangtze River estuary with two national naturereserves is an important ecoregion as it is <strong>the</strong> home for manyeconomically and ecologically important species, and servesas an important stopover site for migratory birds on <strong>the</strong> EastAsian-Australasian Flyway (Chen et al. 2003; Ma et al.2004). However, in common with o<strong>the</strong>r estuaries in <strong>the</strong>world (Cohen and Carlton 1998; Grosholz 2002), <strong>the</strong>Yangtze River estuary is seriously threatened by exoticspecies invasions. Of all <strong>the</strong> invasive exotic species, smoothcordgrass (Spartina alterniflora) introduced from NorthAmerica, has become <strong>the</strong> most harmful exotic plant to <strong>the</strong>salt marshes, leading to multifold consequences to <strong>the</strong>estuary. Over <strong>the</strong> past five years, we have investigated <strong>the</strong>population spread <strong>of</strong> S. alterniflora on two major islands in<strong>the</strong> estuary, Chongming and Jiuduansha, and examined <strong>the</strong>ecosystem-level effects <strong>of</strong> its invasion. This synopsis isbased on <strong>the</strong>se investigations. Detailed reports werepublished elsewhere. (See References for <strong>the</strong> full list.)SPREAD AND DISTRIBUTIONS. alterniflora was intentionally introduced fromAmerica to China in 1979 (An et al. this volume), and was<strong>the</strong>n spread to <strong>the</strong> Yangtze River estuary in <strong>the</strong> mid 1990sboth by natural dispersal and intentional introductions. For<strong>the</strong> purposes <strong>of</strong> ecological engineering, i.e., rapid sedimentaccretion, S. alterniflora was <strong>the</strong>n intentionally introduced totwo large islands in <strong>the</strong> estuary, Jiuduansha (in 1997) andChongming (in 2001 and 2003). On each island a nationalnature reserve had been set aside for conserving nativebiodiversity and maintaining ecosystem integrity. In fact,this invasive plant has invaded almost all <strong>the</strong> mudflats andsalt marshes in <strong>the</strong> Yangtze River estuary (Fig. 1A), S. alternifloraei<strong>the</strong>r colonized tidal mudflats (Fig. 1D) or replacednative plants like Scirpus mariqueter (Fig. 1E) (Chen et al.2004) and Phragmites australis (Wang et al. 2006b), and hasbecome one <strong>of</strong> <strong>the</strong> most abundant species in estuarineecosystems during a period <strong>of</strong> just over 10 years. Our recentdata obtained through remote sensing show that in 2005 S.alterniflora monocultures accounted for 49.4% and 37.0% <strong>of</strong><strong>the</strong> vegetated area in Dongtan (Fig. 1B) and Jiuduansha (Fig.1C) marshlands respectively (Li et al. 2009). Range expansion<strong>of</strong> S. alterniflora still continues in estuarine wetlands.Successful invasions <strong>of</strong> S. alterniflora in <strong>the</strong> YangtzeRiver estuary were <strong>the</strong> result <strong>of</strong> interactions between biotic,abiotic and human factors (Wang et al. 2006a). The “enemyrelease hypo<strong>the</strong>sis” that is used to explain successful invasions<strong>of</strong> exotic plants elsewhere might also apply to those <strong>of</strong> S.alterniflora in <strong>the</strong> Yangtze River estuary. Spartina alterniflorahas a number <strong>of</strong> superior traits such as fast growth, a highlyefficient use <strong>of</strong> resources, a high tolerance to salt and a welldevelopedbelowground system that make it a superiorcompetitor or invader and a potent ecosystem engineer (Li etal. 2009). It is for this latter reason that S. alterniflora waswidely used for erosion control and sediment accretion alongshorelines in <strong>the</strong> Yangtze River estuary (Wang et al. 2006a),which might have directly led to its rapid spread in <strong>the</strong>marshlands. Frequent reclamation in <strong>the</strong> Yangtze Riverestuary has made <strong>the</strong> estuarine ecosystem susceptible to S.alterniflora as areas outside <strong>the</strong> dike exhibit conditions typical<strong>of</strong> early saltmarsh succession, which favor S. alterniflorara<strong>the</strong>r than native plants. Environmental changes (saltwaterintrusion and eutrophication) caused by human activities- 147 -