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Comparison of the Functional Composition of the Overstory and Understory in Disturbed Riparian Forest Communities.

"Plant functional traits (e.g., seed weight) have been shown to provide a mechanistic understanding of how communities respond to disturbance. Historically, riparian ecosystems have experienced flooding as their dominant disturbance regime, however, human occupation of the floodplain has introduced new types of disturbances. This has resulted in altered trait composition, however, no research has compared the functional trait composition of the overstory and understory against different disturbance types (natural and anthropogenic). Therefore, it is unclear if these vegetation layers are responding similarly or differently to a variety of disturbances within riparian ecosystems. Functional trait theory suggests that certain traits are associated with environmental conditions, like those created by disturbance, regardless of species region or growth form. My research project aims to test this hypothesis by comparing the functional composition of the overstory and understory vegetation in disturbed riparian ecosystems.

At the Ebro River Basin in Spain and along the Garonne River in France, restoration and management efforts have resulted in a variety of natural and anthropogenic disturbances, including sites with cleared overstory, overbank flooding, cleared understory, and undisturbed sites. Seven reproductive functional traits (chosen because reproductive strategies influence a species’ ability to respond to disturbance) were collected for 250 species sampled from 99 sites along the Ebro River Basin and Garonne River. Trait composition was quantified by calculating community-weighted means (CWMs) for overstory and understory species at each site. Preliminary data analysis has revealed that across all sites, the understory has significantly heavier seeds on average when compared to the overstory. Additionally, the difference in CWM seed weight between overstory and understory vegetation varies depending on disturbance type. This indicates that the overstory and understory of riparian communities respond differently to disturbance, and the difference is influenced by the type of disturbance at each site."