Flooding disturbances increase resource availability and productivity but reduce stability in diverse plant communities

Abstract

The natural world is increasingly defined by change. Within the next 100 years, rising atmospheric CO 2 concentrations will continue to increase the frequency and magnitude of extreme weather events. Simultaneously, human activities are reducing global biodiversity, with current extinction rates at B1,000 Â what they were before human domination of Earth's ecosystems. The co-occurrence of these trends may be of particular concern, as greater biological diversity could help ecosystems resist change during large perturbations. We use data from a 200-year flood event to show that when a disturbance is associated with an increase in resource availability, the opposite may occur. Flooding was associated with increases in productivity and decreases in stability, particularly in the highest diversity communities. Our results undermine the utility of the biodiversity-stability hypothesis during a large number of disturbances where resource availability increases. We propose a conceptual framework that can be widely applied during natural disturbances.

Plant species richness and functional traits affect community stability after a flood event

“…In June 2013, an extreme flood event with an estimated 200 years average return time occurred across much of Central and Eastern Europe [8,21]. This resulted in moderate flooding in the TBE at the Jena experiment.…”

“…In this case, the presence and low performance of sensitive species may be buffered by the presence of other species that are more tolerant during the disturbance, or have the ability to regrow after the disturbance [15]. Higher diversity communities may also increase ecosystem functions during subsidy-based perturbations owing to the increased probability that a more diverse community contains fast-growing species that capitalize on resource influxes [8]. Community responses to disturbance may therefore be related to particular functional traits (e.g.…”

“…water stress, photoinhibition and reduced photosynthetic rates), causing a decrease in community biomass [4,5]. Fires and floods may increase resource availability, and the effect of the disturbance, in this case, can result in a resource subsidy and an increase in biomass production [5,8] (figure 1). Importantly, as disturbance severity increases, physiological stress may also increase [9].…”

“…underground storage organs and increased root density) may be more tightly associated with subsidy-based disturbances. With increased resource availability below ground, such as during a minor to moderate flood [8], dense roots may increase species and community growth following a flood event. Finally, traits associated with plant phenology may also be important for plant community responses to flooding.…”

“…(2) With stronger flood intensity, increasingly negative effects (stress) should overwhelm the benefits of any resource inputs (subsidies) resulting from the flood. Increased biomass production in higher-diversity communities during mild floods should become weaker with increasing flooding intensity, as fewer species are physiologically capable of persisting during severe stress [8].…”