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

Riparian wetlands are under heavy pressure from hydrological changes p roduced by dam construction and water diversion projects. There has be en ample documentation of the relationship between the extent of flood ing and the composition of shoreline plant communities, yet we have fe w models that allow us to predict the impact of altered flooding regim es on riparian wetlands. In the humid temperate zone, river regulation commonly affects the distribution of two major vegetation types: wood ed wetland and herbaceous wetland. The practice of reducing peak flood s and augmenting minimum river flows is often followed by the successi on of herbaceous to wooded wetland. We used logistic regression models to describe the distribution of wooded wetland as a function of all p ossible combinations of seven hydrological variables. The variables we re chosen to reflect the depth, duration, and time of flooding and wer e calculated for four different time intervals (3, 7, 12, and 18 growi ng seasons). Our best model was a combination of two variables: the la st day of the first flood and the time of the second flood. For three of the four time intervals, the vegetation type was correctly identifi ed 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 te mperate and boreal zone wetlands.