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Phragmites expansion

Katie Berry, Clay Langley, Amarilis Roman, Peter Steiner, and Dana Dudle
Science Research Fellows and Biology Department, DePauw University
Fall semester 2014

Phragmites australis or common reed is an invasive species of wetland grass.  It reproduces sexually through seed and asexually through underground rhizomes and aboveground runners.  Phragmites has colonized the bottom of the abandoned limestone quarry in the DePauw Nature Park, spreading via clonal growth and windborne seeds.  The goal of our study was to investigate the expansion of Phragmites in the Quarry Bottom. 

We mapped patches of Phragmites in the Quarry Bottom.  We categorized patches as large, small, or point:  large patches were over 10 meters in diameter, small patches were 3 to 10 meters in diameter, and point patches were less than 3 meters in diameter.  We used a GPS unit to record waypoints around the perimeter of each patch.  We recorded the density of live stems and presence of flowering stems within a 0.25 m2 quadrat at each waypoint.  We compared our maps of Phragmites with maps of the same area created in previous years. 

The total area of Phragmites increased 18 percent during a four year period.  The number of point patches nearly tripled from 2012 to 2014.  Most of the new point patches formed next to large patches.  The density of live stems was negatively correlated with patch size; there were more live stems at the edges of small patches than the edges of large patches.  The presence of flowering stems was positively correlated with patch size; there were more flowering stems at the edges of large patches than the edges of small patches.

Our results indicate Phragmites is rapidly expanding in the Quarry Bottom.  New patches are colonizing the edges of temporary ponds and are being established by horizontal stems radiating out from larger patches.  Future research should consider options for removal of Phragmites from the Quarry Bottom.