Higher structural connectivity and resistance against invasions of soil bioengineering over hard-engineering for riverbank stabilisation

Abstract

Riparian corridors play an important role for the maintenance of regional biodiversity and ecosystem functions. Riparian forests are even the only semi-natural vegetation strips remaining in many agricultural or urbanised landscapes. In such landscapes, the spatial continuity of riparian vegetation is frequently broken by the construction of stabilisation structures engineered for erosion control. Here, we examined the effects of different riverbank stabilisation structuresfascines (soil bioengineering), ripraps (hard engineering), and mixed-technique (lower-bank ripraps with upper-bank plantings) -on the structural connectivity of their respective riverbanks. We first revisited previously studied stabilisation structures to extend their vegetation sampling to their adjacent riverbanks. Then, for each type of stabilisation structure, we compared community composition, richness and abundance of native and invasive alien species (IAS), and cover of vegetation strata (herbaceous, shrub and tree) between stabilised embankments and their upstream and downstream banks. Results indicated that, although the composition of fascine banks differed from that of their adjacent riverbanks, they fitted nicely in the structural continuity of their riparian surroundings. Differences were likely explained by the proportion of fast-growing woody species (e.g. willows) planted in fascines, which also induced strong reductions in IAS richness and abundances; i.e. propagule "sinks". Conversely, ripraps broke the structural continuity of riverbanks and were heavily dominated by IAS while mixed-technique banks displayed intermediate characteristics. Consequently, we argued that fascines may be the riverbank stabilisation structures displaying highest ecological benefits in terms of habitat quality and connectivity and should be preferred over the other investigated engineering techniques.

A biodiversity-employment framework to protect biodiversity

“…Soil bioengineering also triggers successional dynamics similar to those theoretically found under natural conditions, favouring ecological processes (Tisserant et al, 2020). Moreover, it can contribute to the restoration of ecological corridors (Martin et al, 2020).…”

“…In conclusion, the social-ecological framework makes possible to question the global relationship between soil bioengineering techniques and biodiversity. It goes further than comparing restored river with non-restored or rip rapped riverbanks as it is most frequently done (Schmitt, Schäffer et al 2018, Martin, Janssen et al 2020. Degradation of the ecosystem is a process acting at multiple scales: riverbank restoration through soil bioengineering techniques will be an improvement at a local scale (e.g.…”

The Conservation and Restoration of Riparian Forests along Caribbean Riverbanks Using Legume Trees

“…It improves riparian habitat quality and allows the development of native plant communities during secondary succession [31,32]. Soil bioengineering facilitates the partial recovery of some of the main ecological functions previously provided by riverbanks and now degraded, e.g., ecological corridor, biodiversity support or depollution [28,33,34], and contributes to climate change mitigation through carbon sequestration [35]. Beyond its ability to restore ecosystems, soil bioengineering can also be used as a conservation tool for endangered plant populations [36].…”