Changes in aquatic plant community structure and species distribution at Caddo Lake

Invasive species have influenced the plant community structure at Caddo Lake. The spatial extent of invasive species inventoried in 1995, and plant community types were classified according to their hydrologic regime. Replication of the 1995 study in regularly and semi-permanently flooded habitats in 2005 reveals a shift in plant community structure, with major changes being mostly attributed to the increased prevalence of Eichhornia crassipes (Mart.) Solms (water hyacinth) and Alternanthera philoxeroides (Mart.) Griseb (alligator weed). Detrended correspondence analysis and TWINSPAN classification demonstrate a shift of site-pairs in ecological ordination space. Some invasive species with an importance score of <1% in 1995 became dominant by 2005. T-tests were conducted to test the mean differences of select species between 1995 and 2005; all invasive species significantly changed during the ten-year period. Quantitative data were combined with ArcGIS to demonstrate the significant effects of invasive species in the swamp habitat over time.