Distribution and Drivers of a Widespread, Invasive Wetland Grass, Phragmites australis, in Wetlands of the Great Salt Lake, Utah, USA

The introduced grass Phragmites australis (hereafter Phragmites) is one of the most widespread invasive plants in North American wetlands. Phragmites has been extensively studied in some regions of North America, such as the Chesapeake Bay and the Great Lakes. However, little research has evaluated the extent of Phragmites invasion in the Intermountain West and the environmental drivers that have promoted its spread, particularly in the critically important Great Salt Lake (GSL) wetlands. Here we use high-resolution multispectral imagery to map the current distribution of Phragmites around GSL. We then identify factors associated with Phragmites presence in GSL using a species distribution model using the Random Forest algorithm. We contrast these findings with what is known about Phragmites invasion in other regions. We estimate that Phragmites occupies over 93 km² around GSL. Phragmites was more likely to be found in wetland areas close to point sources of pollution, at lower elevations with prolonged inundation, and with moderate salinities. Results from our study will assist wetlands managers in prioritizing areas for Phragmites monitoring and control by identifying likely areas of prime Phragmites habitat.