Species composition and plant traits: Characterization of the biogeomorphological succession within contrasting river corridors

Abstract

Plant communities and dynamics can be characterized according to species composition or plant traits. Here, we used species composition and plant traits to compare their effectiveness in discriminating the biogeomorphological (involving reciprocal feedbacks between physical and biological processes) and ecological (mainly biologically driven) phases of the fluvial biogeomorphological succession (FBS) model. The comparison was done between two French rivers, the largely unchannelized lower Allier and the channelized middle Garonne. One reach representative of each river section was selected for the study. Within each river reach, we chose two contrasted study sites in terms of channel and floodplain dynamics: a reference site (least altered channel and floodplain dynamics) and an altered site (laterally stabilized by riprap and constrained). In the four study sites, we sampled vegetation in 402 plots of 4 m2. The 512 species identified in the plots were characterized in terms of plant traits (20) from a literature review. When comparing reaches in unconstrained ordinations and permutational multivariate analyses of variance, both species composition and plant traits led to a similar identification of the biogeomorphological and the ecological successional trajectories. Nevertheless, the trait approach was less influenced by local and regional bioclimatic, hydrogeomorphological, and anthropogenic settings and thus produced a more comprehensive and general classification of the biogeomorphological and ecological phases of the FBS model. A lower than expected contrast between the four sites was found, because neither species composition nor plant traits could entirely characterize distinct successional trajectories occurring in our reference or altered sites. Furthermore, our results contributed to a better understanding of the multiple successional trajectories that can occur in midlatitude river corridors. It also showed that relating plant traits to their effects on fluvial landform dynamics remains a core challenge in explaining succession including feedback mechanisms between hydrology, morphodynamics, and vegetation dynamics.

A model study of the combined effect of above and below ground plant traits on the ecomorphodynamics of gravel bars

“…More recently, plant response to disturbances has been hypothesised to be predicted by specific plant functional traits that express the relationships between environmental factors, ecological processes and a given species 9 – 11 , 16 . Trait-based approaches, where plants are grouped depending on their functional traits, have shown to predict well vegetation response to flow regimes 9 , 12 , 13 and changes in biogeomorphic phases 14 . However, a clear understanding on how (functional) vegetation types may influence river ecomorphodynamics remains limited to a handful of studies 15 , 26 .…”

Extending the conceptual model of river island development to incorporate different tree species and environmental conditions

“…The importance of riparian trees for the development and stability of river islands and floodplain margins has been a subject of considerable research attention, especially over the last two decades. Building on understanding of vegetation colonization of disturbed, dynamic riparian zones (e.g., Bornette, Tabacchi, Hupp, Puijalon, & Rostan, 2008; Dykaar & Wigington, 2000; Johnson, 2000; Mahoney & Rood, 1998; Polzin & Rood, 2006) increasing emphasis has been placed on feedbacks between plants and fluvial processes (Dufour, Rodríguez‐González, & Laslier, 2019) and particularly the ways in which plant species may act as “physical ecosystem engineers” (Jones, Lawton, & Shachak, 1997), driving the creation and maintenance of fluvial landforms (e.g., Bendix & Stella, 2013; Bertoldi, Gurnell, & Drake, 2011; Corenblit et al, 2011, 2015; Corenblit, Steiger, Gurnell, Tabacchi, & Roques, 2009; Corenblit, Tabacchi, Steiger, & Gurnell, 2007; Gurnell, 2014; Gurnell et al, 2016; Gurnell, Bertoldi, & Corenblit, 2012; Kollmann, Vieli, Edwards, Tockner, & Ward, 1999; Politti, Bertoldi, Gurnell, & Henshaw, 2018; Tabacchi et al, 2019).…”

“…increasing emphasis has been placed on feedbacks between plants and fluvial processes (Dufour, Rodríguez-González, & Laslier, 2019) and particularly the ways in which plant species may act as "physical ecosystem engineers" (Jones, Lawton, & Shachak, 1997), driving the creation and maintenance of fluvial landforms (e.g., Bendix & Stella, 2013;Bertoldi, Gurnell, & Drake, 2011;Corenblit et al, 2011Corenblit et al, , 2015Corenblit, Steiger, Gurnell, Tabacchi, & Roques, 2009;Corenblit, Tabacchi, Steiger, & Gurnell, 2007;Gurnell, 2014;Gurnell et al, 2016;Gurnell, Bertoldi, & Corenblit, 2012;Kollmann, Vieli, Edwards, Tockner, & Ward, 1999;Politti, Bertoldi, Gurnell, & Henshaw, 2018;Tabacchi et al, 2019).…”

Professor Geoffrey Petts (1953–2018): An outstanding interdisciplinary river scientist

“…Three papers contribute to theme 5 (riparian vegetation and large wood in river dynamics). Tabacchi et al () explore the biogeomorphological succession driven by interactions between plants and physical processes in river corridors, specifically highlighting the importance of species composition and plant traits. Rodríguez et al () also consider interactions between plants and sediments that give rise to patterns of overbank sedimentation within the lower Orinoco floodplain.…”