NMDS ordination of 22 sites in two time periods (1982 and 2010/2011) based on species’ importance values. Grey symbols and arrows represent “old” ponds, black symbols and arrows indicate “young” ponds. Arrows pair the same site in two time periods, the arrowhead indicates the later (2010/2011) sample. Dashed lines indicate biplots of variables with r >0.300. Species centroids of invader and monodominant taxa are indicated. PHRAUS: Phragmites australis, SCHACU: Schoenoplectus acutus, LYTSAL: Lythrum salicaria, POLHYD: Persicaria hydropiperoides, CEPOCC: Cephalanthus occidentalis, TYPHA: Typha × glauca.