Open Archive TOULOUSE Archive Ouverte ( OATAO ) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ- toulouse.fr/ Eprints ID : 11091 To link to this article : doi:10.1002/esp.3515 URL : http://dx.doi.org/10.1002/esp.3515 To cite this version : Corenblit, Dov and Steiger, Johannes and González, Eduardo and Gurnell, Angela M. and Charrier, Gaspard and Darrozes, José and Dousseau, Julien and Julien, Frédéric and Lambs, Luc and Larrue, Sébastien and Roussel, Erwan and Vautier, Franck and Voldoire, Olivier The biogeomorphological life cycle of poplars during the fluvial biogeomorphological succession: a special focus on Populus nigra L. (2014) Earth Surface Processes and Landforms . ISSN 0197- 9337 Any correspondance concerning this service should be sent to the repository administrator: [email protected] DOI: 10.1002/esp.3515 The biogeomorphological life cycle of poplars during the fluvial biogeomorphological succession: a special focus on Populus nigra L. D. Corenblit, 1,2 * J. Steiger, 1,2 E. González, 3 A. M. Gurnell, 4 G. Charrier, 1,2 J. Darrozes, 5 J. Dousseau, 1,2 F. Julien, 6 L. Lambs, 6 S. Larrue, 1,2 E. Roussel, 7 F. Vautier 7 and O. Voldoire 1,2 1 Clermont Université, Maison des Sciences de l ’Homme, 4 rue Ledru, 63057, Clermont-Ferrand Cedex 1, France 2 CNRS, UMR 6042, GEOLAB – Laboratoire de géographie physique et environnementale, 63057, Clermont-Ferrand, France 3 Peatland Ecology Research Group, Université Laval, 2425, rue de l ’Agriculture, Québec, Québec G1V 0A6, Canada 4 School of Geography, Queen Mary, University of London, Mile End Road, London E1 4NS, UK 5 Université Paul Sabatier, CNRS, UMR 5563, GET – Géosciences Environnement Toulouse, Université Toulouse III, F-31062, Toulouse, France 6 Université Paul Sabatier, INP, CNRS, UMR 5245, ECOLAB – Laboratoire écologie fonctionnelle et environnement, Université Toulouse III, F-31062, Toulouse, France 7 CNRS, USR 3550, Maison des Sciences de l ’Homme, 4 rue Ledru, 63057, Clermont-Ferrand Cedex 1, France *Corresponde nce to: D. Corenblit, Clermont Université, Maison des Sciences de l ’Homme, 4 rue Ledru, 63057 Clermont-Ferrand Cedex 1, France. E-mail: [email protected] ABSTRACT: Riverine ecosystems are recurrently rejuvenated during destructive flood events and vegetation succession starts again. Poplars (i.e. species from Populus genera) respond to hydrogeomorphological constraints, but, in turn, also influence these processes. Thus, poplar development on bare mineral substrates is not exclusively a one-way vegetative process. Reciprocal interac- tions and adjustments between poplar species and sediment dynamics during their life cycle lead to the emergence of biogeomorphological entities within the fluvial corridor, such as vegetated islands, benches and floodplains. Based on a review of geomorphological, biological and ecological literature, we have identified and described the co-constructing processes between riparian poplars and their fluvial environment. We have explored the possibility that the modification of the hydrogeomorphological environment exerted, in particular, by the European black poplar ( Populus nigra L.), increases its fitness and thus results in positive niche construction. We focus on the fundamental phases of dispersal, recruitment and establishment until sexual maturity of P. nigra by describing the hierarchy of interactions and the pattern of feedbacks between biotic and abiotic components. We explicitly relate the biological life cycle of P. nigra to the fluvial biogeomorphic succession model by referring to the ‘biogeomorphological life cycle ’ of P. nigra . Finally, we propose new research perspectives based on this theoretical framework. KEYWORDS: biogeomorphology; biogeomorphological life cycle; fluvial biogeomorphic succession model; abiotic-biotic feedback; engineer species; Salicaceae; evolutionary geomorphology Introduction It is widely recognized that certain modifications induced by engineer organisms within their physicochemical environment In geomorphology and ecology, many research projects related provide positive feedback to ecosystem function (Wright and to the role of organisms as geomorphological agents at the Jones, 2006; Fisher et al ., 2007; Hastings et al ., 2007). An illus- Earth surface have been carried out without an established link trative example is the North American beaver ( Castor between the two disciplines. However, disciplinary concepts canadensis Kuhl, 1820), which builds dams and modulates can help to establish an interdisciplinary understanding of func- matter and energy fluxes into rivers (Dawkins, 1982; Naiman tional connections between organisms and geomorphic forms et al ., 1988; Gurnell, 1998; Odling-Smee et al ., 2003; Butler and processes, as for example the concept of ‘ecosystem engi- and Malanson, 2005), leading it to be defined as a ‘keystone neers ’ developed in ecology. According to Jones et al . (1994), species ’ (sensu Paine, 1995) that controls riparian ecosystem an engineer species is defined as a species that exerts a strong structure and function (Wright, 2009). Jones et al . (2010) control over ecosystem function by way of creating or signifi- suggested that modifications of the physical environment by cantly modifying the habitat. engineer organisms, if sufficiently durable (such as in the case of the ones enhanced by C. canadensis ), change selective the fluvial corridor (Edwards et al ., 1999; Gurnell et al ., 2001). pressures within the ecosystem (see also Wright et al ., 2012). The question of whether the emergence of biogeomorphological It has even been hypothesized by Dawkins (1982) that beaver structures such as fluvial islands and floodplains can be related to constructions, and related modifications in selective pressures, a positive NC ( sensu Odling-Smee et al ., 2003) is paramount to enhance their own fitness by selecting the most efficient engi- discerning whether these biogeomorphological entities do have neer-alleles promoting niche construction (NC). Odling-Smee an evolutionary basis (Corenblit et al ., 2011). et al . (2003) defined such feedback as ‘positive NC ’, synony- We suggest that the consideration of this positive bio- mous to the notion of an ‘extended phenotype ’ previously pro- geomorphological feedback between an engineer plant and posed by Dawkins (1982). Niche construction thus is a specific its physical environment requires revisiting its life cycle. Strictly case of ecosystem engineering referring to the situation when speaking, the life cycle of a plant corresponds to its course of selective pressures for the engineer species or others species development through a series of different stages, from the time in the ecosystem is modified through the creation or the modi- of inception to death. A riparian angiosperm life cycle begins fication of the habitat. By definition, according to Odling-Smee with a seed that, in adequate hydrogeomorphological condi- et al . (2003) NC operates with an evolutionary response within tions, will germinate and produce a seedling that will grow to the biologically-modified ecosystem. Positive niche construc- a mature plant over a few years. The mature plant will then tion must be considered as a particular type of NC where the eventually reproduce sexually, forming new seeds, and the next fitness of the ecosystem engineer is improved by the modifica- life cycle will start in the form of a new plant. In a fluvial con- tion of the habitat. text, specific ranges of hydrogeomorphological conditions Riparian plants also drastically modify their hydrogeo- control the successive phases of the life cycle of some ligneous morphological environment through their interaction with plants, from seed release, germination and growth to sexual water and sediment flow during floods (Corenblit et al ., maturity (Braatne et al ., 1996). The objective of revisiting the 2009b; Gurnell, 2013). Over millions of years, aquatic and life cycle of riparian species, especially engineer plants, is riparian plant species have developed efficient traits increasing to relate their biological sequence of development to their fitness in a fluvial environment (Lytle and Poff, 2004; hydrogeomorphological conditions (such as sediment tex- Nakamura et al ., 2007; Nakamura and Inahara, 2007; Bornette ture, deposition rate, relative elevation above the water et al ., 2008). Thus, the chances of riparian plants establishing surface and related exposure to submersion), since they and interacting with hydrogeomorphological processes within are modifiable by the engineer plant during its life cycle fluvial corridors have an evolutionary explanation (Niklas, (Figure 1). 1997). The responses of riparian plants to flood events were Species related to the Populus (Salicaceae) genera (e.g. affected, in the long-term, by past exposure to comparable within the Aigeiros section: the black poplar Populus nigra L. in hydrogeomorphological events. Specific life history, physiolog- Europe, the Eastern cottonwood P. deltoids (Bartr.) Marsh. and ical, morphological and biomechanical adaptations improved Fremont cottonwood P. fremontii S. Wats. in respectively eastern their resistance and resilience within a disturbed, unstable and western North America; within the Tacamahaca section: the and fluctuating environment (Lytle, 2001). As a consequence, Narrowleaf cottonwood P. angustifolia