Figure 5: Observed feedback at the community level. (a)
Herbaceous and arboreous communities in the active tract of the Tech
River and (b) the Allier River. Photographs: Dov Corenblit (a) and
Franck Vautier (b).
Landscape-level feedbacks: biological versus physical
forcing in contrasted hydrogeomorphological contexts
At the scale of the fluvial landscape, our research was carried out
primarily on the Tech, Allier and Isère Rivers, using two and
three-dimensional spatiotemporal analyses with GIS, stereo and
multi-image photogrammetry and LiDAR. These three rivers differ in their
morphodynamics and the level of anthropogenic pressure. The Tech is a
Mediterranean torrential river with a very irregular
hydrogeomorphological regime. Anthropogenic pressure has led to channel
bed vertical incision, lateral stabilization of its banks and therefore
to a certain loss of dynamics despite the virulence of flash floods. The
Allier is a high-energy river that is, in its lower section (RNNVA)
still relatively free to move laterally in a wide meander belt. The
Isère River is a high-energy river that has was laterally confined with
huge embankments. This resulted in a channel mostly straightened and
migrating alternate bars progressively stabilizing and heavily colonized
by vegetation.
Spatial analyses of the feedback between colonization/vegetation
succession dynamics and landscape/fluvial style dynamics on these three
rivers have made it possible to highlight different types of responses
and effects of riparian vegetation at the landscape scale and thus to
estimate the impact of local feedbacks (at the scale of traits and
population) on the organization of the habitat mosaic over few decades
(Fig. 6).