Plant succession in a restored floodplain wetland: 2010-2014
Floodplain wetlands provide vital habitat and food for wildlife as well as serve an important function in filtering overland runoff. This study evaluates the restoration of 16 acres of a floodplain wetland located nine miles south of Pittsburgh, PA between 2010 and 2014. The property was mined for coal in the 1940s and managed as a golf course between 1968 and 1983. Plant community surveys began in 2009, which was the same year the wetland was planted with native vegetation to enhance the restoration process. Ten permanent sampling plots were randomly established in the wetland. At each plot, herbaceous plants were identified and their percent cover was estimated in a one square-meter subplot nested within a larger 400 square-meter subplot in which shrubs and saplings were identified and counted. A more detailed study of sapling growth was conducted by recording annual measurements of trunk diameter and height of targeted species common to floodplain wetlands in southwestern Pennsylvania.
The dominant herbs during all sampling years were creeping jenny (Lysimachia nummularia) and purple loosestrife (Lythrum salicaria), which on average accounted for 52% and 14% of all flowering herbs between 2010 and 2014, respectively. Both herbs are invasive species and threaten the diversity of plants in the wetland. The mean Shannon-Weiner diversity index for herbs is 1.7, which is low compared to healthy wetlands that are more likely to have an index of 3.5. The dominant grass, reed canarygrass (Phalaris arundinacea) is native to Pennsylvania but its aggressive growth is also limiting species diversity. Fox sedge (Carex vulpinoidea) and blunt broom sedge (Carex tribuloides) account for 76% of all sedges and rushes and are experiencing the greatest decline in coverage due to invasive species and natural succession. The sapling species represent a pioneer community dominated by boxelder (Acer negundo), American elm (Ulmus Americana) and more recently, Eastern cottonwood (Populus deltoides). The sapling density has increased from 179 per 400 square meters in 2010 to 267 in 2014. The largest threat to the restoration efforts of the wetland is invasive species.