Dating saltmarshes using tree rings on a halophilous plant

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.