PARENT SESSION
Contributed Oral Session 37: Floodplain Restoration
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 513 A, Level 5, Palais des congrès de Montréal
Restoring fluvial processes: the role of flood inundation in the distribution and abundance of a common riparian shrub.
Fremier, Alexander*,1, Talley, Theresa2, 1 University of California, Davis, Davis, Ca, USA2 University of California, Davis, Davis, Ca, USA
ABSTRACT- Floodplains in large, alluvial rivers around the world are among the ecosystems most heavily impacted by humans through such activities as flow regulation and floodplain constriction. While flood inundation patterns have been shown to control riparian plant distribution and abundance proximate to the river channel, little is known about their effects on plants in upper riparian reaches where fluvial alterations and flooding occur less frequently. Altered hydrology has most likely changed the plant communities of these riparian/upland transition areas, but over longer periods of time and larger spatial extents than are normally considered. We determined the potential effects of flooding on riparian upland plants by examining the relationships between flood inundation patterns and the distribution of a common riparian upland shrub, blue elderberry (Sambucus mexicana) in California. We used both hydrologic variability within rivers and comparisons between dammed and undammed rivers to determine the role of hydrology in elderberry distributions. We found that flooding influenced elderberry age/size class distribution. Higher proportions of young/small shrubs (2-7 cm max. basal diameter) being found nearer to the river, while older/larger shrubs (≥12 cm diam.) increased with distance from the river and elevation relative to the river channel. Similarly, shrubs along the unrestricted river, where flooding was more pronounced, were generally younger/smaller than those along the dammed rivers. Floods appear to limit the long-term survival (decades) of shrubs; the older/larger shrubs found on high elevations and away from the river may be remnant pre-dam recruits. Data suggest that floodwaters contribute to seedling success by providing moisture beyond winter rains. In summary, unrestricted floods historically played a role in the maintenance of riparian ecosystem heterogeneity, including uneven distributions of elderberry age and size structure. Understanding the effects of altered flow regimes on plant population structure will help restoration of floodplains in the absence of a natural flow regime; recommendations are discussed.
Key words: riparian vegetation, flood inundation, dam, Sambucus mexicana