Effects of exotic Spartina alterniflora on the habitat patch associations of breeding saltmarsh birds at Chongming Dongtan in the Yangtze River estuary, China

Abstract

Smooth cordgrass (Spartina alterniflora)is one of the most invasive exotic plants of saltmarshes worldwide. To understand the effects of smooth cordgrass invasion on the habitat use and selection by breeding saltmarsh birds, we compared species number and abundance of breeding birds in native reed (Phragmites australis) and smooth cordgrassinvaded habitats (reed-cordgrass mixed habitats and cordgrass monocultures) at Chongming Dongtan in the Yangtze River estuary, China. We further examined the similarity of bird communities in different habitats and habitat selection by dominant bird species. For saltmarsh generalists, species number and abundance did not differ among the habitats. For saltmarsh specialists, species number and abundance did not differ in reed monocultures and reedcordgrass mixed habitats but were significantly lower in cordgrass monocultures than in reed monocultures and reed-cordgrass mixed habitats. ANOSIM indicated that the difference in bird communities was larger between cordgrass monocultures and the habitats with reed than between the habitats with reed. The saltmarsh specialists preferred reed monocultures, while saltmarsh generalists avoided reed monocultures. Most species indicated no selection (neither preferred nor avoided) on reed-cordgrass mixed habitats, and no species preferred the cordgrass monocultures. The use of cordgrass monocultures by the common saltmarsh birds was negatively related to their body size. This study suggests that the spread of exotic smooth cordgrass has greatly affected the species composition and structure of local bird communities and has been especially disadvantageous to the saltmarsh specialists.

Bird species richness and abundance in riparian vegetation invaded by exotic Reynoutria spp.

“…In contrast, a generalist species like Sylvia atricapilla were not affected by the invasive plant. This pattern corresponds to the findings of a study from China which compared bird responses to the invasion of exotic grass Spartina alterniflora Loisel among species differing in the level of habitat specialization in Yantze River estuary (Ma et al 2011). Here the generalist species did not show any effect of the exotic plant invasion but the specialists were adversely affected.…”

Migratory Waterbirds Response to Coastal Habitat Changes: Conservation Implications from Long-term Detection in the Chongming Dongtan Wetlands, China

“…8). Previous studies indicated that the mudflat and shallow water habitat might be replaced by the Scirpus habitat because of the natural succession of the vegetation community (Zhao et al 2009); however, these two types of habitats were drastically replaced by the invasive Spartina habitat in the past decades (Gan et al , 2010Ma et al 2011;Zhao et al 2009). Thus, the negative correlation between the waterbird populations (species number and density) and the mudflat and shallow water habitat might not infer the negative effect of such habitat to waterbirds.…”

“…6) and became one of the most dominant plants. As an invasive plant, Spartina habitats, characterized by tall and dense vegetation and reduced diversity and abundance of food resources, are difficult for waterbirds' foraging (Guntenspergen and Nordby 2006;Gan et al 2009Gan et al , 2010Ma et al 2011). In its native range (e.g., northeastern North America), however, Spartina habitats are suboptimal for foraging waterbirds.…”

“…The corms and seeds of Scirpus and the invertebrates in these habitats brought by spring tides are the main food sources for waterbirds (Yu et al 1995). Spartina and Phragmites habitats, characterized by tall and dense vegetation and reduced diversity and abundance of food resources, are unavailable to waterbirds Guntenspergen and Nordby 2006;Ma et al 2011). Deep water habitats and aquaculture ponds are also suitable habitats for waterbirds, especially swimming waterbirds (Ma et al 2004;Tian et al 2008).…”

“…Spartina habitats gradually replaced the native plant communities (i.e., Scirpus and Phragmites) and became one of the most dominant plants in the intertidal flats. The areas invaded by Spartina, which are characterized by tall (>1 m) and dense vegetation and reduced diversity and abundance of food resources, significantly affected the species composition and the waterbird community structure, especially saltmarsh specialists (Gan et al 2010;Guntenspergen and Nordby 2006;Ma et al 2011). Artificial wetlands can compensate for the loss of natural wetlands to some extent (Elphick 2000;Zhang et al 2011;Zhao et al 2003); however, natural wetlands have been found to support a greater number of avian species than artificial wetlands in some areas (Ma et al 2004;Tourenq et al 2001).…”