Litter legacy increases the competitive advantage of invasive Phragmites australis in New England wetlands
- 445 Downloads
Exotic plant invaders that form monocultures and exclude native plants are often the most detrimental to native diversity and the hardest to eradicate. To generate a monoculture, the invader must garner more resources than resident natives and, once established, persist despite high densities of conspecific neighbors. Coincident with expansion and long-term persistence, successful invaders typically accumulate senesced material, but the role of this litter in mediating the invader’s ability to establish and maintain monospecific dominance has rarely been investigated. We used stands of the common reed, Phragmites australis, a prolific wetland invader in North America, to explore the impact of litter on interspecific competition with the native rush, Juncus gerardii, and intraspecific competition among live shoots. In 10 × 10 m areas positioned on Phragmites expansion fronts, we removed litter to isolate its effect from live Phragmites on light availability, aboveground biomass and community composition. Compared to adjacent, unmanipulated fronts, light availability nearly tripled and Juncus biomass increased >170% in litter removal areas after 4 months. Although the positive response of Juncus and native forbs was most pronounced on the leading edge of Phragmites stands, litter removal triggered a 271% increase in native plant biomass even in the interior of stands where Phragmites’ live stem density was highest. Litter treatment did not significantly affect Phragmites biomass, but more, shorter stems emerged in litter removals revealing Phragmites modifies stem phenotype in response to local litter and light conditions. These results suggest that litter plays a central role in Phragmites’ invasion process, from initial establishment to subsequent monospecific dominance. Thus, prescribed litter removal may be an effective strategy to enhance coexistence of native plant populations in wetlands where eradication of invasive monocultures is not an ecologically or economically feasible option.
KeywordsCompetition Intraspecific interactions Invasive species Juncus gerardii Monoculture Tidal marsh Wetland management
We would like to thank T. Savage, N. Herrmann and M. K. Lane for assistance in the field, J. Griffin, B. Bolker and B. R. Silliman for comments on the manuscript, and the Brown Undergraduate Teaching and Research Award program and RI Sea Grant for funding support.
- Quinn GP, Keogh MJ (2002) Experimental design and data analysis for biologists. Cambridge University, Cambridge, UKGoogle Scholar
- Warren RS, Fell PE, Grimsby JL, Buck EL, Rilling GC, Fertik RA (2001) Rates, patterns, and impacts of Phragmites australis expansion and effects of experimental Phragmites control on vegetation, macroinvertebrates and fish within tidelands of the lower Connecticut River. Estuaries 24:90–107. doi: 10.2307/1352816 CrossRefGoogle Scholar