Role of storm activities on the spread of an invasive plant, Phragmites australis, in North America

Background/Question/Methods

Alterations of habitat characteristics by natural and/or anthropogenic disturbances have been considered as one of the primary facilitators of biological invasions. Large scale disturbances such as hurricanes and tropical storms are frequent in the Gulf and Atlantic coasts of North America and might enhance the spread of invasive species by altering habitat characteristics and helping dispersal of propagules.  However, no studies have examined the role of hurricanes and storm activities on species invasion.

The spread of a Eurasian haplotype of Phragmites australis in North America in the past century offers a model system to examine the effect of large scale disturbances on plant invasion. In this study, we examined if storm activities enhance the spread of P. australis in the wetlands of North America. This species produces large monotypic stands that can be identified in aerial images and followed backward in time. Using a series of aerial images, we quantified the growth (change in area) rates of P. australis patches in 19 wetlands along the coasts of Gulf of Mexico, Atlantic Ocean, the Great Lakes and the Great Salt Lake. The effects of the frequency and intensity of storms on the growth rates of P. australis patches were evaluated.

Results/Conclusions

Frequency of hurricanes and storms with maximum sustained wind speeds exceeding 50 knots at the study sites had a significant positive effect on the growth rate of P. australis patches. Intensity of storms (quantified as the summations of hurricane categories, and maximum sustained wind speeds at a time period) also had a significant positive effect on the growth rate of patches. Storm frequency and intensity explained greater variation on patch growth rates in the sites along the Gulf and Atlantic coasts. These results suggest that hurricane and storm activities enhance the spread of P. australis in the coastal wetlands of North America. In the context of global climatic change which is expected to increase the frequency and intensity of the storm activities, these findings may help providing a link between global climate change, erratic weather patterns and the spread of invasive species.