The effect of small disturbances on germination and emergence of Phragmites australis in brackish wetlands

Background/Question/Methods Phragmites australis is invading wetland communities across the United States and has resulted in declines of native plant and animal diversity and alterations to nutrient cycling. Our objective was to understand how small disturbances allow for the invasion of the invasive strain of Phragmites. A survey of disturbances across four native plant communities (Spartina patens/Distichlis spicata, Schoenoplectus americanus, Iva frutescens, and Typha angustifolia) showed that the majority were caused by deer, muskrats, and humans. An experiment tested the emergence of Phragmites seeds and rhizomes in artificially created disturbances, imitating those most commonly found in the survey, across these same plant communities. We planted seeds and rhizomes in one of three disturbance types within each plant community: a control, an above ground disturbance (minor disturbance), or a below ground disturbance (severe disturbance). Results/Conclusions We found that seed germination increased significantly (3.7X) in the less inundated plant communities with an increase in disturbance severity; we attribute this to higher light levels, higher temperatures, and less flooding. There was low Phragmites seed germination in the more inundated plant community where light levels and temperatures were lower and flooding more frequent. Rhizome emergence was consistently low (8.6%) across all plant communities and disturbance treatments. We predict that Phragmites is most likely to invade by seed in disturbed, less flooded marsh communities