Monitoring of restored vegetation in the wetlands of Wolf Lake, Hammond, Indiana

Background/Question/Methods

Wolf Lake is a lagoon located in the southern shore of Lake Michigan.  Much of the native characters of the lake have been lost by human activities since the end of the 19^thcentury.  It has been partitioned into several pools by causeway, railroad and dikes, filled with slags (waste from steel mills), and excavated for sand extraction.  Consequently, all islands within the lake have disappeared and the shorelines have been infested by exotic plants.  In 2007, US Army Corps of Engineers recreated 17 islands totaling 62 ha, removed exotic plants in a portion (1.5 km) of the lake’s shoreline, and reintroduced 146 native plant species in both the islands and the shoreline.  We initiated a monitoring of the restored vegetation in 2012.  We established a total of 285 plots (2 m x 2 m).  In each plot, we identified all plants to species, estimated cover for each species using point contact method, and compared with pre-restoration data that were collected in 2001.

Results/Conclusions

Our NMS (Non-metric Multidimensional Scaling) ordination revealed an apparent conversion from exotic- to native-dominated vegetation in the shoreline.  Prior to the restoration, >66% of the shoreline vegetation was dominated by 33 species of exotic plants, most notably purple loosestrife (Lythrum salicaria), Kentucky bluegrass (Poa pratensis), white sweet clover (Melilotus alba) and Eurasian reed (Phragmites australis).  The relative importance of native species has increased from <34% to 87% in the shoreline and to 95% in the upland plots after the restoration.  Among the 83 native species that established after the restoration, three-square bulrush (Scirpus pungens) was most dominant in both the shoreline and the upland, followed by green spikerush (Eleocharis palustris) in the shoreline and by hardstem bulrush (Scirpus acutus) in the upland.  Meanwhile, Eurasian milfoil (Myriophyllum spicatum) remained as the most dominant macrophyte species as it constituted 15% and 25% of the total frequency before and after the restoration, respectively.  The data collected from this survey will be used as a baseline for further monitoring.