Vegetation Cover Dynamics and Resilience to Climatic and Hydrological Disturbances in Seasonal Floodplain: The Effects of Hydrological Connectivity.

Linlu Shi,Guangchun Lei,Li Wen,Cai Lu,Yifei Jia,Yuyu Wang

doi:10.3389/fpls.2017.02196

Abstract

Floodplain wetlands are valuable ecosystems for maintaining biodiversity, but are vulnerable to hydrological modification and climatic extremes. The floodplain wetlands in the middle Yangtze region are biodiversity hotspots, particularly important for wintering migratory waterbirds. In recent years, extremely low winter water level events frequently occurred in the middle Yangtze River. The hydrological droughts greatly impacted the development and distribution of the wet meadows, one of the most important ecological components in the floodplains, which is vital for the survival of many migratory waterbirds wintering in the Yangtze region. To effectively manage the wet meadows, it is critical to pinpoint the drivers for their deterioration. In this study, we assessed the effects of hydrological connectivity on the ecological stability of wet meadow in Poyang Lake for the period of 2000 to 2016. We used the time series of MODIS EVI (Enhanced Vegetation Index) as a proxy for productivity to infer the ecological stability of wet meadows in terms of resistance and resilience. Our results showed that (1) the wet meadows developed in freely connected lakes had significantly higher resilience; (2) wet meadows colonizing controlled lakes had higher resistance to water level anomalies; (3) there was no difference in the resistance to rainfall anomaly between the two types of lakes; (4) the wet meadow in freely connected lakes might approach a tipping point and a regime shift might be imminent. Our findings suggest that adaptive management at regional- (i.e., operation of Three Gorges Dam) and site-scale (e.g., regulating sand mining) are needed to safeguard the long-term ecological stability of the system, which in term has strong implications for local, regional and global biodiversity conservation.

Highlights

Riparian floodplains are areas adjacent to rivers that are periodically flooded (Junk, 1989)
The opposite but synchronous trends between water level at Xingzi and the enhanced vegetation index (EVI) in controlled sub-lakes indicated the negative impacts of water level on the development of wet meadows
Ecological stability is closely associated with flood regimes (Colloff and Baldwin, 2010), which in term are driven primarily by the flow regimes of the associated rivers (Opperman et al, 2009)

Summary

Introduction

Riparian floodplains are areas adjacent to rivers that are periodically flooded (Junk, 1989) They are hydrologically important (e.g., flood mitigation), environmentally sensitive (e.g., regulating climate), and ecologically productive areas that perform many natural functions and services (Costanza et al, 1997; Dudgeon et al, 2006; Acreman and Ferguson, 2010). Hydrological Connectivity and Vegetation Stability is important to sustain regional and global biodiversity (Shiel et al, 1998; Selwood et al, 2017) Despite their high productivity and vital ecological functions and services, floodplains are among the most endangered landform types worldwide (Millennium Ecosystem Assessment, 2005; Nilsson et al, 2005); and hydrological alternation is one of the most excessive anthropogenic pressures threating the ecological integrity of floodplains (Graf, 2006; Arias et al, 2014; Cochrane et al, 2014; Zarfl et al, 2015). Long-term measurements of ecological state are useful to calculate resistance and resilience (De Keersmaecker et al, 2015; Wen and Saintilan, 2015; Ivits et al, 2016; Verbesselt et al, 2016), and changes in the two metrics provide an indication/early warning of imminent irreversible changes in equilibrium states (De Keersmaecker et al, 2016)

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Conclusion