swales) that persist for hundreds to thousands of years. Medium power 

 flood events, which occur at an intermediate frequency, affect ecosystem 

 structures that exist from decades to hundreds of years. He identified 

 tree species associations as an ecosystem component likely to be influ- 

 enced at this scale. The low power, high-frequency flood events occcur 

 annually and affect short-term patterns such as seed germination and 

 seedling survival. His characterization emphasized the dramatic impact 

 flooding has on the regeneration of vegetation in bottomland forests. 



Grubb (1977) stated that scientists have failed to understand ade- 

 quately how plant communities maintain themselves because of a failure 

 to account for the phenomenon of regeneration in plant communities. 

 Huenneke and Sharitz (1986) , in a study of microsite abundance and dis- 

 tribution of woody seedlings in a South Carolina cypress- tupelo swamp, 

 concluded that the availability and nature of microsites may affect the 

 distribution and composition of the seedling and sapling strata, thus 

 differentiating the "regeneration niche" described by Grubb. 



Although plant species association is determined by a number of 

 interacting environmental factors, it is generally agreed that flooding 

 is the dominant environmental factor at work in bottomland forests, 

 affecting regeneration and life under saturated soil conditions. Flood- 

 ing persisting for more than a few days will prevent the replenishment 

 of soil oxygen once the soil microbes and plant roots consume the avail- 

 able soil oxygen in the root zone during respiration. Only those plant 

 species that have evolved a mechanism for living in reducing (anaerobic) 

 soil conditions will survive such conditions. In most instances, recur- 

 ring flooding provides a competitive advantage for plant species that 

 are adapted to saturated and reduced soils. 



