RIVER HYDROLOGY AND RIPARIAN WETLANDS: A PREDICTIVE MODEL FOR ECOLOGICAL ASSEMBLY

Riparian wetlands are under heavy pressure from hydrological changes pro- duced by dam construction and water diversion projects. There has been ample documen- tation of the relationship between the extent of flooding and the composition of shoreline plant communities, yet we have few models that allow us to predict the impact of altered flooding regimes on riparian wetlands. In the humid temperate zone, river regulation com- monly affects the distribution of two major vegetation types: wooded wetland and herba- ceous wetland. The practice of reducing peak floods and augmenting minimum river flows is often followed by the succession of herbaceous to wooded wetland. We used logistic regression models to describe the distribution of wooded wetland as a function of all possible combinations of seven hydrological variables. The variables were chosen to reflect the depth, duration, and time of flooding and were calculated for four different time intervals (3, 7, 12, and 18 growing seasons). Our best model was a combination of two variables: the last day of the first flood and the time of the second flood. For three of the four time intervals, the vegetation type was correctly identified as herbaceous or wooded for >80% of the sample points. Our results suggest that models based on a few key environmental variables can be valuable tools in the conservation management of the vegetation of tem- perate and boreal zone wetlands.

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