Dating saltmarshes using tree rings on a halophilous plant
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ORIGINAL PAPER
Dating saltmarshes using tree rings on a halophilous plant Laurent Godet
. Armelle Decaulne
. Cle´ment Poirier
Received: 1 September 2020 / Accepted: 11 September 2020 / Published online: 24 September 2020 Springer Nature B.V. 2020
Abstract Dating saltmarshes is a fundamental step to conserve them suitably, because the oldest saltmarshes are becoming increasingly rare and host a particular biodiversity. In a French Atlantic saltmarsh, we counted tree rings on Suaeda vera, a ligneous plant of the European saltmarshes. We considered that the age of the stem may give the minimal age of the saltmarsh on which it grows as this is a specialist species of this habitat. By combining the dating of the saltmarsh using this proxy with a classical dating based on a photo-interpretation method, we found that the count of tree rings on S. vera gives an accurate dating of the minimal age of a saltmarsh patch. However, because of the rather low longevity of this species (maximum of 27 years in the investigated area), old maps and aerial photographs still remain essential to date the oldest saltmarsh patches. We further discuss: (1) the potential use of cross-dating on dead stems of the plant to reconstruct the long-history of saltmarshes; (2) the potential link between the growth velocity of S. vera and the spatial dynamics of saltmarshes.
L. Godet (&) A. Decaulne CNRS, Universite´ de Nantes, UMR LETG, B.P. 81223, 44312 Nantes Cedex 3, France e-mail: [email protected] C. Poirier Normandie Universite´, UNICAEN, UNIROUEN, CNRS, M2C, 14000 Caen, France
Keywords Arc¸ay Conservation Ageing Coastal Photo-interpretation Mapping
Introduction Saltmarshes are often considered as the most productive ecosystems on Earth (Whittaker 1975; Dame and Kenny 1986). They play a key role in coastal trophic food webs as they support fish nurseries (Daiber 1977; Costa et al. 1994, 1995). Saltmarshes also contribute to storm surge mitigation through dissipation of wave energy by vegetation (Mo¨ller et al. 2014). The fauna and flora living in saltmarshes are original because they are highly specialized to cope with particular environmental pressures, among which salinity fluctuations and daily covering and uncovering by the tides are the most important (Adam 1999). These habitats often cover very restricted areas in the world coastal zones (Meire and Kuijen 1988 in Descender and Maelfait 1999) and have been submitted to strong anthropogenic pressures for centuries, among which land reclamation (for European examples see Goeldner-Gianella 2000; Boorman 2003; Verger 2009; Godet et al. 2015), grazing and haying (Bakker 1983; Dijkema 1984; Parkinson 1985) are the strongest. Long-term saltmarsh evolution depends on the balance between tide and wave currents, sediment supply, vegetation growth and sea level rise (e.g. Best
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et al. 2018), the latter being expected to negatively affect saltmarsh stability (Adam 2002). Despite the recognition of their specific b
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