Detecting the effects of biological invasion and subsequent control efforts on wetland ecological processes

Abstract

Meadow and emergent cattail wetland communities in eastern North America are being replaced by an invasive lineage of <i>Phragmites australis</i>. This invasion has consequences for wetland ecosystem functions; including macronutrient storage due to invasion-driven changes in net primary productivity, decomposition rates and altered environmental site conditions. Because <i>P. australis</i> invasion degrades wetland ecological integrity, extensive efforts to control <i>P. australis</i>, mainly through herbicide application, have been undertaken. While the effects of <i>P. australis</i> control efforts on recovering plant communities has been studied, the success of these efforts at restoring ecosystem functions to pre-invasion ranges is unknown. My objectives were to 1) quantify the effect of <i>P. australis</i> invasion on macronutrient storage in the annual vegetative standing stock compared to uninvaded meadow and cattail marshes, and 2) to evaluate the success of large-scale, herbicide-based <i>P. australis</i> control efforts at re-establishing rates of net primary productivity, decomposition and environmental conditions to levels comparable to those in uninvaded marsh. I conclude that the effect of invasion on macronutrient storage was dependent on the plant community being replaced. Significant increases in annual macronutrient vegetative standing stock were observed when <i>P. australis</i>-dominated marsh was compared to meadow marsh, but few differences were observed between <i>P. australis</i> and cattail marsh. My analysis also revealed a reduction in carbon sequestration services one-year post-herbicide application. Emergent plant community recovery will likely be critical to increasing carbon sequestration in herbicide-treated marsh. My work indicates that <i>P. australis</i> invasion and subsequent control efforts represent trade-offs in ecosystem services. <i>Phragmites australis</i> invasion can increase macronutrient storage in the marsh but decrease biodiversity, and <i>P. australis</i> control efforts aiming to increasing biodiversity reduce carbon sequestration, at least temporarily. Understanding these net effects of <i>P. australis</i> invasion and control efforts on wetland functions informs decision makers considering whether to attempt <i>P. australis</i> eradication.