5.2. Isère River landscape: dominance of biological forcing
in-between dikes in a highly anthropized context
The intricate interplay between hydrogeomorphological processes and
riparian vegetation can play a pivotal role in shaping the fluvial
landscapes within highly-confined rivers. Corenblit et al. (2020a)
studied the reciprocal coupling between river morphodynamics and
vegetation succession in the Isère River, France, where human
intervention in the form of lateral confinement with embankments and
straightening had a transformative impact on riverine landscape dynamics
(see also Vautier, 2000; Vautier et al., 2002).
Using GIS analysis of historical aerial photographs spanning nearly five
decades, from 1948 to 1996, the authors showed that a remarkable
biogeomorphological transformation unfolded as the once mobile
transverse gravel bars began a gradual but significant colonization by a
diverse array of vegetation types. This situation presented an
opportunity to understand the temporal adjustments between fluvial
landforms and vegetation succession stages, ultimately culminating in
the establishment of mature riparian forests on stabilized alternate
bars. This biogeomorphological trajectory of change was a direct
consequence of feedbacks between hydraulics, sediment transport, and
vegetation dynamics in a highly impacted river reach. The mosaic of
vegetated bars that emerged was an outcome of the strong bioconstruction
and biostabilization effects exerted by pioneer vegetation on bars of
differing ages, sizes, and mobility within the riverine landscape.
Field measurements undertaken in 1996 provided tangible evidence of a
robust positive feedback loop between sediment dynamics and the ongoing
riparian vegetation succession (Vautier, 2000). In the complex balance
between physical and biotic adjustments, the vegetated bars evolved as
emergent biogeomorphological entities specifically resulting from the
biogeomorphological feedbacks of sediment accretion, topographic raise,
and vegetation growth and succession. Co-inertia analysis (CoIA), a type
of ordination statistical technique used for exploring and understanding
bi-directional relationships between two or more data tables or
matrices, permitted the quantification of the intricate relationships. A
highly significant statistical association between geomorphological and
vegetation variables (as exemplified by an RV value of 0.41, p
< 0.001) was found. This association explained a staggering
95% of the variability along just one axis, demonstrating the existence
of an exceedingly robust feedback loop between geomorphological changes
and vegetation succession.
To appreciate the full significance of these findings, we must turn our
gaze to the broader context of the theoretical model of fluvial
biogeomorphological succession based on positive feedback loops between
fluvial morphodynamics and vegetation succession (FBS model; Corenblit
et al., 2007). The empirical observations from the Isère and Tech Rivers
both allowed the validation of the FBS model, suggesting that this model
is applicable to natural but also channelized rivers.