PARENT SESSION
Oral Session # 79: Forest Ecology V: Structure; Dispersal; Competition.
Presiding: J Schnurr
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 104.
Fifty years of change in the floodplain forests of the lower Wisconsin River.
Hale, Brack*,1, Alsum, Esther1, 1 University of Wisconsin-Madison, Madison, WI, USA
ABSTRACT- Recent studies of several Midwestern floodplain forests revealed these forests are shifting to Acer saccharinum dominated communities. This trend is troubling, as the diversity of the overstory vegetation drives the diversity of the forest ecosystem. In this study, we analyze the changes that have occurred in the floodplain forests of one of the Midwest′s longest free-flowing stretches of river, the Lower Wisconsin, over the last 50 years and investigate the impact of several anthropogenic factors on forest composition and structure: river regulation, overabundant herbivore populations, and timber harvests. We resurveyed five locations surveyed in the 1950′s, as well as five other representative sites along the Lower Wisconsin. Preliminary analysis indicates the forests today have a lower diversity than 50 years ago (H′ =1.38 and 1.54 respectively), although sites where timber harvests had occurred showed increased diversity. At a species level, A. saccharinum has greatly increased in abundance. Further, this trend appears to be transitory, as A. saccharinum is almost completely absent from the understory. Early-successional species and Ulmus americana have decreased in importance, while two relatively minor species in the 1950′s have gained importance, Celtis occidentalis and Carya cordiformis. The understory has seen dramatic increases in two thorny shrubs, Rhamnus cathartica and Zanthoxylum americana, indicating that species possessing herbivore defenses may possess a strong competitive advantage in this system. Overall, the results reveal the forests of the Lower Wisconsin are at a later stage of succession than they were 50 years ago, an indication of the reduced flooding regime of the river. Timber harvests appear to play a role in maintaining some disturbance and encouraging the growth of certain species. However, they do not completely replace the importance of floods as the major form of disturbance.
Key words: floodplain forests, Lower Wisconsin River, woody species