Mapping invasive Phragmites australis in highway corridors using provincial orthophoto databases in Ontario

Abstract:

We mapped the distribution of invasive Phragmites australis (European common reed) in MTO-operated roadways of southern Ontario using airphotos from a provincial database, the Southwestern Ontario Orthophotography Project (SWOOP), which covers all highways from Windsor east to Norfolk/Niagara and north to Tobermory. We mapped all available SWOOP images acquired in 2006, 2010 and 2015. In addition, we delineated invasive Phragmites along MTO-operated roadways within the footprint of the Southcentral Ontario Orthphotography Project (SCOOP acquired in 2013) and the Central Ontario Orthophotography Project (COOP acquired in 2016); the mapping excludes the Greater Toronto Area but includes Prince Edward county, roads through the city of Barrie, and north to Parry Sound. Based on available orthophotos for SWOOP only, total areal cover of invasive Phragmites expanded an order of magnitude between 2006 and 2010 (26.8 to 259.7 ha, respectively); between 2010 and 2015, there was only an increase of 7.2% (278.4 ha), presumably because of ongoing herbicide treatments that began on selected roads beginning in 2012. Expansion rate differed between road types, with 400-series highways having significantly greater expansion rates than non-400 highways (24.5 vs 6 times, respectively). Areas covered by SCOOP images had an areal cover of 152 ha in 2013, while that for COOP images had an areal cover of 7.8 ha in 2016. This inventory is freely available for anyone to update using provincial orthophotos or medium to high-resolution satellite imagery such as Sentinel 2.