Small Changes in Flooding Have Large Consequences: Experimental Data from Ten Wetland Plants

Abstract

Flooding regime is a major determinant of vegetation composition in wetlands. Flooding regimes are also commonly altered by human activity. We used an experimentally-created elevation gradient on mineral soil to measure the responses of ten common marsh species to flood regimes ranging from 0 to 100 % of the growing season. We asked three questions. (1) What are the minimum and maximum tolerances of these ten species to a flood duration gradient? (2) Is there one duration of flooding that is physiologically optimal for a majority of the species? (3) How sensitive are these species to minor changes in flood duration? We found that the number of species, the cover and the aboveground biomass were highest when flood duration was less than a third of the growing season. All species showed a pattern of inclusive fundamental niches for flooding duration, with a preference for shorter periods of flooding, for less than a third of the growing season. Narrow-leaved graminoids became relatively more common with longer flooding duration. This study challenges our notions of the fundamental niches of these wetland emergent plants. Other factors beyond flooding tolerance must be acting to structure wetland communities along wetland depth gradients.