Restoration of a Danube floodplain forest: what happens to species richness of terrestrial beetles?

Abstract

Along the upper Danube, between river kilometer 2,472 and 2,464 (Bavaria, Germany), a managed hardwood forest was reconnected to the river via a newly carved floodplain channel. We report the stepwise alteration of the diversity of terrestrial beetles for six successive years from 2007 to 2012. In a 2‐year preliminary period (2007–2008), we recorded the baseline stage before the technical measures were implemented (2009–2010) and the onset of restoration occurred (2011–2012) with a continuous water flow in the new channel and seven flooding events. Each sample plot was equipped with a pitfall trap, an emergence photo‐eclector, an arboreal photo‐eclector, and a flight interception trap in breast height and in the canopy, respectively. The beetle communities act as an indicator to detect possible disturbance events when a riparian hardwood forest is stepwise transformed to become a new floodplain ecosystem. Within the 6‐year study period, we trapped 62,107 individual beetles, representing 85 families, 544 genera, and 1,191 species. Compared to the baseline stage, the abundance and the number of species decreased, including rare and red list species. On functional level, the species decline was particularly pronounced for zoophagous and mycetophagous species. Finally, we suppose that the 2‐year period since the launch of the new channel is too short for the establishment of a beetle community adjusted to the terrestrial part of the developing new floodplain forest.

Changes in carabid diversity indicate successful restoration of riparian habitats

“…The preferred habitats of P. areolatus are less vegetated gravel banks (GAC, 2009) which is also valid for Bembidion modestum , Bembidion punctulatum , and Omophron limbatum . Habitat heterogeneity increases with increasing river dynamic leading to a mosaic of unvegetated sand and gravel patches, sparse vegetation as well as later successional stages at a distance from the shore and floodplain forests which is beneficial for diverse riparian carabid assemblages (Gruppe et al, 2018; Januschke et al, 2014; Paillex et al, 2017).…”

“…Although relatively little time had passed since the restoration in 2018, restoration success already became apparent. This was all the more remarkable as many studies show that it usually takes a longer time before positive effects occur (Gruppe et al, 2018;Kedzior et al, 2016). Of course, with an increase of only three indicator species, one must be cautious at first glance, but together with the fact that stenotopic riparian species also increased, positive effects of the restoration were emerging.…”

“…We evaluated temporal changes (before vs. after = BA) and considered effects across the different site types 'managed' (control site), 'natural' (control site) and 'restoration' (impact site) (control vs. impact = CI). In this context, carabid beetles are excellent bioindicators in riparian habitats (Bednarska et al, 2018;Gruppe et al, 2018;Januschke & Verdonschot, 2016;Januschke et al, 2011Januschke et al, , 2014Paillex et al, 2017) as they respond quickly to environmental changes (Gerisch et al, 2012;Lambeets et al, 2009). This is because carabid beetles have specific demands for habitat conditions (Günther & Assmann, 2005;Kleinwächter & Rickfelder, 2007;Paetzold et al, 2008) and comprise numerous well-adapted riparian species (Cartron et al, 2003;Gerisch et al, 2012;Lambeets et al, 2008).…”