Flood protection can compromise plant protection

Posted on July 1, 2013

 Because flooding promotes the exchange and recycling of nutrients and organic matter between aquatic and terrestrial ecosystems, it might be expected that structures designed to  mitigate the impacts of flooding, such as levees, will tend to limit biodiversity.  However, until recently this assumption had never been formally tested.  To fill this gap in knowledge, streamside vegetation at 11 sites on three rivers in Yorkshire, U.K. was surveyed in late summer.  Paired sites with and without flood defences were selected to reduce the level of spatial variation in the data, and areas affected by mowing or grazing were avoided.  The number and diversity of plant species (59 species in total) were significantly higher in riparian areas without levees than in those with levees (29 species).  These results were consistent with the idea that flood disturbance at undefended sites opens up more “gaps” that are then available for invasion by new species. To maximise riparian plant diversity, soft engineering approaches to flood management that don’t isolate the floodplain from the stream channel are to be preferred. 

Reference:  Pettifer, E. & Kay, P.  2012.   The effects of flood defences on riparian vegetation species richness and abundance.  Water and Environment Journal 26, 343–351.