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Mapping areas invaded by Phalaris arundinacea in Navigation Pools 2-13 of the Upper Mississippi River

De Jager, N. R., E. E. Hoy, and J. J. Rohweder, J.J.  2017.  Mapping areas invaded by Phalaris arundinacea in Navigation Pools 2-13 of the Upper Mississippi River.   A completion report submitted to the U.S. Army Corps of Engineers’ Upper Mississippi River Restoration Program from the U.S. Geological Survey, 2017L2. 20 pp. with maps.

Abstract

Phalaris arundinacea (Reed canarygrass) is an aggressive invader of North American wetlands. Although Phalaris has received local attention from land managers on the Upper Mississippi River (UMR) floodplain, a lack of information about its current abundance and distribution has made it difficult to quantify the magnitude of invasion or target areas for restoration actions. We used, or otherwise modified, existing GIS data to isolate: 1) open wet meadow areas that are currently dominated (>80% cover) by Phalaris, 2) forested areas with Phalaris present in the understory, and 3) forests with more open canopies that are potentially susceptible to Phalaris encroachment in the future. Estimates of all three areas were spatially variable across the portion of the UMR we studied (Navigation Pools 2-13). Taking into consideration both the proportion of wet meadows dominated by Phalaris and the presence of Phalaris in the forest understory, Navigation Pools 4, 7, 8 and 9 appear to support large areas showing signs of invasion (>62% of wet meadow area and > 30% of sampled forest area). This represents a total area of at least 5,730 ha. Although the majority of floodplain forest in these pools is considered closed canopy (>66% cover), maps of the area of open forest canopy can be used to identify forest areas that may be at risk of future invasion.  Management agencies can use the maps developed to target areas for Phalariseradication, to protect existing native plant communities, or to promote forest regeneration in areas near Phalaris wet meadows.

Keywords

Invasion, floodplain, forest canopy, forest regeneration