Clonal integration and the expansion of Phragmites australis

The recent expansion of the reed Phragmites australis in western Atlantic s alt marshes has become a conservation concern. Historically, Phragmites was restricted to the terrestrial border of marshes, but now it aggressively i nvades lower elevations. To explore factors influencing this expansion, we examined (1) the effects of physical factors and competitive interactions o n the performance of Phragmites and (2) the role of clonal integration on t he ability of Phragmites to invade low marsh habitats. We transplanted Phragmites into vegetation along an elevation gradient, wit h and without neighboring plants. Phragmites died when transplanted to the lowest marsh zone but survived and expanded in higher marsh zones. This sug gests that the low oxygen availability characteristic of waterlogged soils limits Phragmites growth in the low marsh. Neighboring vegetation reduced P hragmites growth in all zones, and severing Phragmites rhizomes invading th e low marsh reduced the survivorship and photosynthetic rate of ramets. These results suggest that Phragmites may invade low marsh habitats by init ially establishing itself in the high marsh and then expanding into lower, less favorable habitats using clonal integration. This has important implic ations for understanding the changing dynamics of New England salt marsh pl ant communities and developing management strategies for the control of Phr agmites.