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Fine‐grained sediment deposition alters the response of plant CSR strategies on the gravel bars of a highly regulated river

Abstract : Aims In riverine ecosystems, variations in disturbance and stress intensities along the flood gradient shape vegetation community structure. However, human modifications to the flood regime may change the magnitude of disturbance and stress, leading to different species distribution patterns along environmental gradients. We aimed to study the effects of local- and broad-scale environmental gradients on riparian plant CSR (Competitors-Stress tolerators-Ruderals) strategies along a highly regulated river. Location Rhone River, France. Methods We assessed how changes in elevation, fine sediment and temperature influenced CSR strategies of riparian plant communities, by studying variations in the community-weighted means and the functional dispersion of the CSR values, on gravel bars along a 250 km north-south river corridor. Results Species with contrasting ecological strategies co-occurred less on gravel bars subject to fine sediment deposition, leading to patterns of biotic homogenization along the flood gradients. Furthermore, a shift in CSR strategies from ruderal to stress-tolerant communities occurred along the elevation gradient on bars with low proportions of fine sediments and from stress-tolerant to ruderal communities along the elevation gradient on bars with high proportions of fine sediments. Regarding the climatic gradient, the mean value of ruderals increased with temperatures. Also, for stress tolerators, the dispersion value diverged between the northern and southern gravel bars when the proportion of fine sediments was low and converged when the proportion of fine sediments was high. Conclusions Overbank fine sedimentation alleviates the intensity of stress along not only the elevation gradient but also the climatic gradient. By homogenizing the functional composition of communities, this process may have detrimental consequences for riparian plant diversity, especially of ruderal plants in the littoral zone. In regulated river systems, restoration measures should therefore promote an increase in the intensity of: (a) disturbance through the reactivation of bedload supply and transport; and (b) stress through increased flow dynamics.
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https://hal.archives-ouvertes.fr/hal-03025207
Contributor : Hervé Piégay Connect in order to contact the contributor
Submitted on : Thursday, November 26, 2020 - 2:30:01 PM
Last modification on : Sunday, June 26, 2022 - 2:58:38 AM
Long-term archiving on: : Saturday, February 27, 2021 - 7:22:24 PM

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Philippe Janssen, Hervé Piégay, André Evette. Fine‐grained sediment deposition alters the response of plant CSR strategies on the gravel bars of a highly regulated river. Applied Vegetation Science, 2020, 23 (3), pp.452-463. ⟨10.1111/avsc.12494⟩. ⟨hal-03025207⟩

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