PARENT SESSION
Symposium 2: Biological Invasions: Species Exchanges Between Eastern Asia and North America.
Organized by: YD Choi, RN Mack, S Maio, and H Li
Monday, August 2, 8:00 AM to 11:30 AM, Oregon Ballroom 203.
Invasions of Asian plants in the wetlands of Great Lakes reion.
Choi, Young1, 1 Purdue University Calumet, Hammond, IN, 46323
ABSTRACT- Invasions of Asian species into North America date back to the late Cretaceous Period (75 million years BP). Exchanges of terrestrial species, mostly unidirectional from Palearctic to Nearctic, across the Beringia during most of the Cenozoic Era have contributed to the similarities of vegetation in eastern North America and eastern Asia; numerous species in both regions were identified as congeners. Located in the same latitudinal range (30-40o N), the two regions share similar geological histories and climates. Invasions of Asian species have particularly been favored in the degraded habitats with similar physical environment of their North American counterparts. Such invasions impose two major concerns for management and conservation of native biota: (1) hybridization of native species with their non-native congeners leading to "genetic swamping"; and (2) formation of monospecific colony of non-native species and exclusion of native species. Hybridization of native Typha latifolia and "likely" non-native Typha angustifolia into Typha x galuca and monospecific stands of Asian haplotype of Phragmites australis are examples of the former and the latter in the degraded wetlands of Great Lakes states and provinces. Our study suggests that the expansion of Phragmites is a part of multi-step process of floristic degradation, initiated by hydrological alterations, as follows: (1) expansion of Typha angustifolia in impounded wetlands; (2) build-up of litter mounds by Typha stands; (3) invasions of Phramites in the litter mounds with lowered water table; (4) exclusion of Typha by Phragmites in rhizome competition; and (5) reallocation of energy to the aboveground biomass in monospecific stands of Phragmites. Restoration of natural hydrology needs to be preceded the control of these invasive species since the degradation process is a symptom of altered hydrology.
Key words: invasions, Asian, typha, phragmites