The impact of experimental sedimentation and flooding on the growth and germination of floodplain trees Ramona L. Walls 1,2, * , Denice Heller Wardrop 1 and Robert P. Brooks 1 1 Penn State Cooperative Wetlands Center, 302 Walker Building, The Pennsylvania State University, University Park, PA 16802, USA; 2 Current address: Department of Ecology and Evolution, State University of New York Stony Brook, Life Sciences Building, Stony Brook, NY 11794-5245, USA; * Author for correspondence (tel.: 1 (516) 885-8005; fax: 1 (631) 632-7626) Received 20 August 2002; accepted in revised form 23 March 2004 Key words: Acer rubrum, Fraxinus pennsylvanica, Quercus palustris, sediment, wetlands, floodplains, adventi- tious roots Abstract Land-use changes in a forested floodplain’s watershed can lead to incremental changes in the hydrology and sedimentation rates of the floodplain. The impacts of these changes can be difficult to measure due to the slow response time of mature trees. Seedlings and saplings, on the other hand, may show an immediate response. Responses during these early life history stages can have major consequences for regeneration of floodplain for- ests and ultimately result in community alteration. This study tested the importance of changes in hydrology and sedimentation on the germination and growth rates of three common floodplain tree species: Acer rubrum, Fraxi- nus pennsylvanica and Quercus palustris. Two-year-old saplings were grown in a greenhouse under two hydro- logic regimes, with or without the addition of sediment. Neither periodic flooding with or without sediment nor static flooding on its own affected the growth of the seedlings. With the addition of sediment, static flooding for two weeks lead to a significant decrease in sapling growth. There was a significant species x treatment interac- tion, suggesting that each species responded differently to the application of flooding and sediment. The timing of germination and the total percent germination for F. pennsylvanica and Q. palustris seeds were tested under the same conditions. Flooding and sediment acted in an additive manner to delay the germination of both F. pennsylvanica and Q. palustris and to reduce the total germination rate of Q. palustris. There was no difference in the total germination rate of F. pennsylvanica seeds under any treatment. During the growth trials, adventitious roots sprouted on saplings grown under sedimentation. Adventitious roots growing into sediment rather than floodwater should be able to utilize the sediment’s nutrients and may compensate for some of the stress of flood- ing. The results of this study suggest that sediment tolerances will vary among species, but will not necessarily correlate with flood tolerances, and that sedimentation may be as important as flooding in determining floodplain plant community composition. Introduction Riparian forests are the most extensive class of wet- lands in the contiguous United States Mitsch and Gosselink 2000. They play an important role in pro- viding wildlife habitat, maintaining water quality and preventing catastrophic flooding Johnson and Mc- Cormick 1979; Taylor et al. 1990; Jordan et al. 2003. Riparian forests are part of the hydrogeomorphic class of mainstem floodplains, wetlands whose primary structuring factors are their sedimentation and hydrologic regimes Golet et al. 1993; Cole et al. 1997; Lenssen et al. 1999. Floodplains in the north- eastern United States are situated in historically for- Plant Ecology 2005 176:203-213 © Springer 2005