Abstract
Research in fluvial biogeomorphology largely aims to promote our understanding of the interactions between riparian vegetation and fluvial morphodynamics within riverine ecosystems. Starting at the end of last century, Angela M. Gurnell has made a major contribution to fluvial geomorphology by considering, in addition to water flow and sediment transport, explicitly riparian, and later also aquatic vegetation and thus significantly promoted the fluvial biogeomorphological approach from its beginnings until today. The objective of the present paper is to present a set of studies and results obtained over the last twenty years by the authors and many collaborators, including Angela M. Gurnell, on a panel of French rivers: Tech, Garonne, Isère and Allier Rivers. In particular, feedback mechanisms between fluvial morphodynamics and riparian vegetation dynamics were investigated directly in the field and also using high resolution remote sensing at the scale of individual plants, populations, communities and landscapes, as well as during semi-controlled ex situ experiments at the scale of individual plants. Collectively, the authors’ research conducted over the past 20 years contributed to elucidate some key aspects of the feedback dynamics between the lowest and highest levels of the riparian ecosystem organisation. This article presents and discusses those key aspects. The gradually obtained results contributed to better understand and quantify feedbacks between river morphodynamics and vegetation at nested spatiotemporal scales, from plant species traits to the riverine landscape. Furthermore, the biogeomorphological approach advocated for more than twenty years now, has clearly helped to contribute to the enlargement of the discipline of geomorphology to ecology as well as evolutionary ecology, and to the development of a more integrative vision to study earth surface processes.
Keywords: Fluvial biogeomorphology, biogeomorphological feedback, riparian vegetation, Populus nigra , black poplar, ecosystem engineer, plant traits.
Introduction
In order to fully understand river behaviour and trajectories of change, Angela M. Gurnell early pointed out the need to study interactions between the biological and physical compartments of ecosystems, i.e., the responses of organisms to the physical environment and their effects on that physical environment (Gurnell and Gregory, 1984, 1995; Gurnell, 1995). Research in fluvial biogeomorphology largely aims to promote our understanding of the interactions between riparian vegetation and fluvial morphodynamics within riparian ecosystems. Angela M. Gurnell has made a major contribution by considering explicitly vegetation, first riparian (living vegetation, propagules and large woods) and then aquatic, in addition to water flow and sediment transport into fluvial geomorphology and thus to promote the fluvial biogeomorphological approach from the end of the last century until today (e.g., far from exhaustive: Gurnell, 1997; Gurnell et al., 2000, 2001, 2004, 2005, 2006, 2012, 2013, 2016a, 2016b, 2018, 2019; Gurnell and Petts, 2002, 2006; Gurnell, 2014; Gurnell and Grabowski, 2016; Gurnell and Bertoldi, 2020; Gurnell and Bertoldi, 2022). A bibliographic research on the Web of Science (all databases) using the combined terms ”riparian vegetation” + ”geomorphology” + ”river*” showed that out of a total number of 711 articles archived on 11th November 2023, more than 12% were authored or co-authored by A.M. Gurnell, which represents 86 articles. The second-best score is 33 articles (Fig. 1).
The biogeomorphological approach applied to rivers is necessarily ambitious because requires skills in geomorphology and plant ecology and because the modalities of interactions between hydrogeomorphological components and riparian vegetation are multiple and nested at various spatiotemporal scales. Thanks to Angela M. Gurnell’s influential research and contribution to fundamental and applied river sciences, fluvial biogeomorphology is now well situated at the interface between, geomorphology, ecology and river management (e.g., Gurnell et al. 2016a,b).