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Community resilience following extreme disturbances: The response of ground beetles to a severe summer flood in a Central European lowland stream



Extreme environmental events are predicted to increase in future due to global climate change. However, their effects on biodiversity still remain insufficiently understood because of the rarity and consequently the difficulty of studying the effects of extreme events. Here, we investigate the impacts on ground beetles of an unpredictable catastrophic flood event of the Elbe River in Germany in the year 2002 using pre- and post-flood data. We analysed the response of grassland communities differentially exposed to flooding and focused on the question of how long their response lagged behind this extreme flood.

Ground beetles were sampled from 1998 to 1999 (pre-flood period) and from 2002 to 2006 (post-flood period) on 48 floodplain grassland plots with a stratified randomized sampling design. Community resilience was quantified by calculating changes in species richness, species abundances, Simpson diversity and beta diversity of ground beetle assemblages.

Ground beetles showed low resistance but high resilience to the extreme flood. Species richness decreased strongly immediately after the flood but reached pre-flood values 2 years later. However, beta diversity remained relatively high in the subsequent years indicating persistent shifts in species composition and abundances. Contrary to our expectation, assemblages inhabiting plots prone to flooding, expected to be less sensitive to floods, did not recover faster than those on rarely inundated plots.

We considered both the timing and the long duration of the flood as main reasons for the low community resistance to the flood. Strategies related to dispersal and habitat generality are identified to be crucial for the quick community recovery following the extreme flood. Our results endorse that extreme floods are integral parts of functioning floodplain ecosystems and that species can cope well even with such unpredictable extreme events, although recovery time tends to be longer than after normal floods. Copyright © 2010 John Wiley & Sons, Ltd.