Proceedings of the Third International Conference on Invasive ...

Chapter 3: Ecosystem Effects <strong>of</strong> Invasive Spartina<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaFig. 1A) Locations <strong>of</strong> Jiuduansha and Chongming Dongtan in <strong>the</strong> Yangtze River estuary, on each <strong>of</strong> which a national nature reserve was set up in 2005 (Li etal. 2009); B) and C) Distribution <strong>of</strong> S. alterniflora in Chongming Dongtan and Jiuduansha marshlands in 2005; D) Conversion <strong>of</strong> tidal mudflats to S.alterniflora meadows; and E) Replacement <strong>of</strong> S. mariqueter with S. alterniflora.might also facilitate fur<strong>the</strong>r invasions in <strong>the</strong> estuary (Wang etal. 2006a, b).PLANT COMMUNITIESOne <strong>of</strong> <strong>the</strong> threats <strong>of</strong> invasive exotic plants to nativeecosystems is <strong>the</strong>ir competitive effects on native plantbiodiversity. Our experimental studies showed that S.alterniflora had great competitive effects on native plantspecies in <strong>the</strong> estuary, e.g., S. mariqueter, which is endemicto <strong>the</strong> Yangtze River estuary (Chen et al. 2004; 2005b) andP. australis (Wang et al. 2006b), which resulted in <strong>the</strong>reduced abundance and even local extinction <strong>of</strong> <strong>the</strong>se nativeplants. In particular, <strong>the</strong> decline <strong>of</strong> S. mariqueter abundancehas been dramatic, which may have important consequencesto shorebird communities because this sedge serves as foodfor shorebirds and creates favorable habitats for <strong>the</strong> birds(Ma et al. 2009; Li et al. 2009).SOIL BIOTIC COMMUNITIESNematodes are important components <strong>of</strong> <strong>the</strong> soilecosystem and play important roles in ecosystemfunctioning. The changes in composition <strong>of</strong> plantcommunities are believed to affect <strong>the</strong> structure <strong>of</strong> nematodecommunities (Yeates 1999). We compared <strong>the</strong> structure <strong>of</strong>soil nematode communities among native (S. mariqueter andP. australis) and S. alterniflora communities on Chongming,Jiuduansha Islands and Nanhui (Chen et al. 2007b). Therewere no significant differences among <strong>the</strong> three plantcommunities in total density <strong>of</strong> nematodes, <strong>the</strong> number <strong>of</strong>genera, or in <strong>the</strong> diversity indices. However, S. alterniflorainvasions altered <strong>the</strong> trophic structure <strong>of</strong> nematodecommunities in soil. The relative abundance <strong>of</strong> bacterivoressignificantly increased, whereas that <strong>of</strong> plant feeders andalgal feeders declined in S. alterniflora communities,compared with that in P. australis and S. mariquetercommunities. Our fur<strong>the</strong>r experimental study demonstratedthat <strong>the</strong> changes in nematode communities were <strong>the</strong> result <strong>of</strong>altered litter quality due to <strong>the</strong> replacement <strong>of</strong> native plantsby S. alterniflora (Chen et al. 2007a).Similarly, we compared <strong>the</strong> structure <strong>of</strong> macrobenthicinvertebrate communities between S. mariqueter and S.alterniflora communities at Chongming Dongtan (Chen etal. 2005a). No significant difference in total density <strong>of</strong>macrobenthic invertebrates was detected between <strong>the</strong> twoplant communities although <strong>the</strong> relative abundance <strong>of</strong> somecommon species was altered, ei<strong>the</strong>r increased or decreased.One <strong>of</strong> our recent studies also showed that S. alternifloraprovided compatible habitats for <strong>the</strong> native crab Sesarmadehaani by <strong>of</strong>fering moderate environmental conditions- 148 -