Vegetation Structure and Composition in Small Forested Wetlands and Their Associations With Water Table Dynamics

Hydrology underpins wetland ecology and vegetation characteristics, but there are few detailed studies on the ecohydrology of north-temperate forested wetlands, specifically on water table dynamics and various metrics of vegetation composition and structure. Using regression and redundancy analysis (RDA), we examined how woody- and ground-vegetation attributes are associated with wetland hydroperiod and other parameters of water table dynamics in forested wetlands within Gatineau Park, Canada. Hydroperiod (i.e., wet period duration) was the most important predictor for tree density and regeneration, and ground vegetation diversity. However, it was not associated with differences in tree community (coniferous vs. hardwood). The average water table position (WTP) of the wet period best explained variations in dead tree size and shrub abundance, and the median WTP was the only significant predictor for tree health. The dry period standard deviation of WTP was the best predictor for woody vegetation wetland species abundance. Similarly, the growing season median WTP explained the most variance in tree height, and average WTP was a better predictor of ground vegetation wetland species abundance, whereas the standard deviation was the best predictor of hardwood-coniferous tree proportion. The final RDA model found 62% of the total variance in vegetation variables to be explained by hydrometric variables, and the most important covariates were the growing season average WTP, hydroperiod, and wet period median WTP. Our results show that hydrometric variables of the growing season WTP as well as separate WTP statistics for both wet and dry periods, can help elucidate vegetation-hydrology associations in forested wetlands.