Differing Drivers of Plant Communities in Flooding vs. Non-flooding Sites
Kelly Steinberg1,2
1Department of Biology, University of New Mexico, Albuquerque, NM, USA; ksteinberg@unm.edu
2Bosque Ecosystem Monitoring Program, Albuquerque, NM, USA; ksteinberg@unm.edu
Today’s cottonwood/willow (Populus/Salix) riparian forests were established when flooding was the most influential ecosystem driver. However, much of the riparian area is now disconnected from the river’s flood regime. Efforts to restore natural flooding regimes have highlighted the importance of flooding in maintaining Populus/Salix plant communities, but these restoration projects can only reach small areas. Much of the land covered by riparian forests are unable to flood, and there is much less known about plant communities where flooding is no longer a potential driver. Using a 15 year dataset of vegetation cover from the Middle Rio Grande Valley we investigated how climate and groundwater differ as potential drivers of plant communities in riparian areas where flooding can and cannot occur. Diversity and species richness of plant communities differed between flooding and non-flooding sites, with exotic species (mostly Tamarix) accounting for much of the differences between the site types. While changes in plant communities were significantly related to groundwater depth and temperature at all sites, variability in groundwater throughout the year appeared to be a driver of plant communities at non-flooding sites. At sites that do not flood, increased variability negatively impacted overall native plant cover, while positively impacting exotic plant cover. Several species show a strong relationship with water variability. With predictions for an increasingly variable climate in the Southwest over the next century, understanding the relationships between variability and riparian vegetation could be vital to maintaining those areas that no longer flood.