Diverging response patterns of terrestrial and aquatic species to hydromorphological restoration

Abstract

Although experiences with ecological restoration continue to accumulate, the effectiveness of restoration for biota remains debated. We complemented a traditional taxonomic analysis approach with information on 56 species traits to uncover the responses of 3 aquatic (fish, macroinvertebrates, macrophytes) and 2 terrestrial (carabid beetles, floodplain vegetation) biotic groups to 43 hydromorphological river restoration projects in Germany. All taxonomic groups responded positively to restoration, as shown by increased taxonomic richness (10-164%) and trait diversity (habitat, dispersal and mobility, size, form, life history, and feeding groups) (15-120%). Responses, however, were stronger for terrestrial than aquatic biota, and, contrary to our expectation, taxonomic responses were stronger than those of traits. Nevertheless, trait analysis provided mechanistic insights into the drivers of community change following restoration. Trait analysis for terrestrial biota indicated restoration success was likely enhanced by lateral connectivity and reestablishment of dynamic processes in the floodplain. The weaker response of aquatic biota suggests recovery was hindered by the persistence of stressors in the aquatic environment, such as degraded water quality, dispersal constraints, and insufficient hydromorphological change. Therefore, river restoration requires combined local- and regional-scale approaches to maximize the response of both aquatic and terrestrial organisms. Due to the contrasting responses of aquatic and terrestrial biota, the planning and assessment of river restoration outcomes should consider effects on both components of riverine landscapes.

Lowland stream restoration by sand addition: Impact, recovery, and beneficial effects on benthic invertebrates

“…This increased occurrence of rheophilic taxa showed the importance of longitudinal connectivity in recovery processes (Lake, Bond, & Reich, ). Pilotto et al () pointed out that the positive responses of aquatic organisms to restoration projects might be related to a combination of local and regional‐scale approaches. By tackling local hydromorphological improvements in a stream stretch and at the same time connecting restored sites to sites with high‐quality macroinvertebrate source populations, streams may benefit most from restoration efforts.…”

“…It is expected that by decreasing the channel dimensions over a relatively large spatial scale, inundation of the stream valley during spates would be stimulated, resulting in less streambed erosion and in turn an increase in instream hydromorphological habitat heterogeneity that sustains a higher biodiversity. By reconnecting the stream to its valley, it is anticipated that land–water gradients can recover, revitalizing both the stream and the riparian zone (Pilotto et al, ). Yet it is not known whether this novel measure of sand addition is actually effective in terms of biodiversity improvements.…”

Effect of river restoration on life-history strategies in fish communities

“…Restoration effects may be reduced in fragmented rivers, affecting the dispersal capacity of the surrounding species pool (Stoll et al, 2014, Kominoski et al, 2018. It is also well known that restoration outcomes can vary over time, as succession processes affect the abiotic characteristic of restored river reaches as well as the communities that establish (Stoll et al, 2014;Pilotto et al, 2018;Thomas et al, 2015). In fish communities, Höckendorff et al (2017) showed how post-restoration successional processes lasted approximately five to eight years before reaching a level of relative ecological stability.…”

Reintroduction of freshwater macroinvertebrates: challenges and opportunities

“…Although subsequent evaluations often confirm an improvement in physico‐chemical conditions and macro‐scale morphological habitat quality (Palmer et al, ), these improvements have rarely achieved the desired outcome for the aquatic community (Palmer et al, ; Haase et al, ). Benthic macroinvertebrates, in particular, often show no substantial increase in population densities, species richness or trait diversity in response to restoration activities (Palmer et al, ; Louhi et al, ; Pilotto et al, in press).…”