Characterizing Past and Modelling Future Spread of Phragmites australis ssp. australis at Long Point Peninsula, Ontario, Canada

Abstract

Non-native Phragmites australis ssp. australis (hereafter Phragmites) is well-established and spreading at the Long Point Peninsula. It is threatening biodiversity, making it a high priority for management. Detailed studies on rates of spread and growth patterns at the landscape-scale are needed for better informed management efforts. In this study, the spatial characteristics of Phragmites in Big Creek and Long Point National Wildlife Areas were quantified using airphoto delineations from 1945 to 2013. Three management units differing in size, habitat, and source of anthropogenic disturbance were compared. Boosted regression tree models were employed to predict future distributions to 2022. Dramatic increases in Phragmites cover (14–37% annually) far exceeding previous detections were measured starting in the mid-1990s. Dispersal was an important factor (14–66%) for spread. Expansion rates were highly variable and increased with longer perimeters. Major predicting factors were proximity to existing stands, vegetation class, and elevation. Vulnerable habitats were characterized as low lying, low sloped, marsh and shallow aquatic vegetation, and areas near water and development. Under static water-levels, Phragmites is predicted to continue spreading at near current rates to 2022 and may begin to encroach into drier habitats.

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