Process of Floristic Degradation in Urban and Suburban Wetlands in Northwestern Indiana, USA

• Published in: Natural areas journal 2003-10, Vol.23 (4), p.320-331
• Main Authors: Choi, Young D., Bury, Carolyn
• Format: Article
• Language: English
• Subjects: Calumets; Creeks; Forest canopy; Grasses; Lythrum salicaria; Marshes; Phalaris arundinacea; Phragmites australis; Populus deltoides; Salix; Salix interior; Salix nigra; Turkeys; Typha; Typha angustifolia; Vegetation; Watersheds; Wetlands; Woodlands
• ISSN: 0885-8608; 2162-4399

We investigated processes of floristic degradation of urban and suburban wetlands in the Turkey Creek and Little Calumet River watersheds in northwestern Indiana, USA. A total of 103 degraded wetland sites were classified into ponds, marshes, woodlands, and forests using Detrended Correspondence Analysis (DCA) ordination. Ponds (83.5 ± 3.8% open water surface) with peripheral vegetation along the shorelines were formerly wetlands but had been deepened by artificial excavation; marshes were characterized by extensive herbaceous cover (89.8 + 3.7%, mostly with Typha angustifolia L.); woodlands retained extensive herbaceous cover (72.1 ± 3.6%) but were subjected to encroachment of woody species (46.5 ± 5.2%, mostly with Salix interior Rowlee and Salix nigra L.); and forests had significant canopy closure by trees (84.0 ± 4.1%, mostly with Populus deltoides Marsh.). The DCA also provided trajectories of floristic degradation as follows: (1) expansions of Typha angustifolia in the impounded wetlands and Phalaris arundinacea L. in the drained wetlands; (2) invasions of Phragmites australis (Cav.) Trin. ex Steud. on litter mounds of Typha stands; (3) invasions of Lythrum salicaria L. in disturbed patches especially adjacent to major highways and local roads; (4) encroachment of woody species, such as Salix spp. and Populus deltoides, in the drained wetlands or the wetlands with significant litter accumulations; and (5) invasions of exotic woody species. The floristic degradations in our study appeared to be symptoms of altered hydrology, and restoration of natural hydrology prior to the removal of invasive plants appeared to be crucial for restoration of native vegetation. Investigamos procesos de degradación floristica en humedales urbanos y suburbanos en las cuencas de Turkey Creek y Little Calumet River, en el noroeste de Indiana, USA. Un total de 103 sitios de humedales degradados fueron clasificados en charcas, pantanos, montes, y bosques usando ordenación por medio de Detrended Correspondence Analysis. Las charcas (85.5 ± 3.8% de la superficie de agua abierta) con vegetación periférica sobre sus orillas fueron inicialmente humedales pero han sido profundizados por la excavación artificial; los pantanos se caracterizaron por la gran extensión de cobertura herbácea (89.8 ± 3.7%, mayoritariamente Typha angustifolia L.); los montes mantuvieron una extensa cobertura herbácea (72.1 ± 3.6%) pero estuvieron sujetos a invasión de especies leñosas (46.5 ± 5.2%, mayor