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The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise. While vegetation is known to facilitate sediment accretion at the plant scale by trapping mineral sediments and producing organic matter, the long- term impact at the landscape scale is still poorly understood. Here we use the biogeomorphic model Demeter to reveal contrasting vegetation impacts on spatial patterns of sediment accretion under different sea level rise regimes. Under contemporary sea level rise rates (2-10 mm/yr), vegetation inhibits sediment transport from tidal channels to platform interiors and creates levee- depression patterns. Hence, intertidal platforms accrete slower with vegetation than without, but this trend attenuates with increasing sea level rise rate, as water depth increases, and vegetation drag decreases. Under extreme sea level rise rate (20 mm/yr), platform interiors don’t keep up and turn into open water, while vegetation allows to preserve intertidal levees. Our results help to better understand some basic biophysical mechanisms that will control the fate of coastal wetlands under global climate change.

The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise. While vegetation is known to facilitate sediment accretion at the plant scale by trapping mineral sediments and producing organic matter, the long-term impact at the landscape scale is still poorly understood. Here we use the biogeomorphic model Demeter to reveal contrasting vegetation impacts on spatial patterns of sediment accretion under different sea level rise regimes. Under contemporary sea level rise rates (2-10 mm/yr), vegetation inhibits sediment transport from tidal channels to platform interiors and creates levee-depression patterns. Hence, intertidal platforms accrete slower with vegetation than without, but this trend attenuates with increasing sea level rise rate, as water depth increases, and vegetation drag decreases. Under extreme sea level rise rate (20 mm/yr), platform interiors don’t keep up and turn into open water, while vegetation allows to preserve intertidal levees. Our results help to better understand some basic biophysical mechanisms that will control the fate of coastal wetlands under global climate change.

The paleobotanist Philippe Gerrienne was internationally renowned for his work on early land plants. His research career was however not limited to the study of Devonian floras. He also actively contributed to the progress of Belgian Wealdian (Early Cretaceous), early Paleogene and Quaternary research. In this framework, Philippe’s interest for Paleogene plants already appeared when he helped to sort Stockmans’ paleobotanical collections of the Royal Belgian institute of Natural Sciences (RBINS) during a civil service he did between 1987 and 1989. In the old conservatoires, he discovered hundreds of silicified trunks and branches from the “upper Landenian” (early Eocene) of Belgium, which were collected in 1970 in the area of Hoegaarden during the construction of the Brussels-Liège highway (E40-A3). From 1994, the RBINS developed new research activities in early Paleogene Belgian sites. At this occasion, fossil plants discovered next to vertebrates from the warm earliest Eocene at Dormaal were studied in collaboration with the Royal Museum for Central Africa, which owns an excellent xylotheque of tropical woods (Doutrelepont et al., 1997). This first step allowed in 1999, after several preliminary works, to start a partnership with the University of Liège (ULiège) and the University of Mons (UMons) through a F.R.F.C.-I.C. (FNRS) project, leaded by Muriel Fairon-Demaret (ULg), on the "Reconstruction of the terrestrial ecosystems in Belgium during the Palaeocene-Eocene transition, 50-60 million years ago". During three years (1999-2002), numerous fieldworks in Belgium and research activities in labs were realized, including a first database of more than 600 hundreds fossil wood specimens. In this overview, I summarize the main accomplishments that have been done in the field. At Péruwelz, we found a silicified trunk fragment of a new arborescent Ericaceae in the marine Thanetian (Upper Paleocene), which was named Agaristoxylon garennicum (Gerrienne et al., 1999). The paleoenvironment of Dormaal was reconstructed based on fruits and seeds from the Paleocene Eocene Thermal Maximum (Fairon-Demaret & Smith, 2002). The most successful work was probably the study of the in situ monospecific Glyptostroboxylon forest of Overlaar at Hoegaarden (Fairon-Demaret et al., 2003). This warm Everglades-like paleoenvironment attracted the Belgian media and finally led to the construction of the geopark of Hoegaarden. In 2004, Philippe described the Givetian (middle Devonian) seed precursor Runcaria heinzelinii Stockmans, 1968 from Ronquières, Belgium (Gerrienne et al., 2004). The rediscovery of the 385-million-year-old basal seed plant and, the same year, the retirement of his close colleague Muriel Fairon-Demaret focused definitively his interest on the Paleozoic. References Doutrelepont, H., Smith, T., Damblon, F., Smith, R. & Beeckman, H., 1997. Un bois silicifié de peuplier de la transition Paléocène-Eocène de Dormaal, Belgique. Bulletin de l'Institut royal des Sciences naturelles de Belgique, 67, 183-188. Fairon-Demaret, M. & Smith, T., 2002. Fruits and seeds from the Tienen Formation at Dormaal, Paleocene-Eocene transition in eastern Belgium. Review of Palaeobotany and Palynology, 122, 47-62. Fairon-Demaret, M., Steurbaut, E., Damblon, F., Dupuis, C., Smith, T. & Gerrienne, P., 2003. The in situ Glyptostroboxylon forest of Hoegaarden (Belgium) at the Initial Eocene Thermal Maximum (55 Ma). Review of Palaeobotany and Palynology, 126, 103-129. Gerrienne, P., Beeckman, H., Damblon, F., Doutrelepont, H., Fairon-Demaret, M. & Smith, T., 1999. Agaristoxylon garennicum Gerrienne et al., gen. et sp. nov., an arborescent Ericaceae from the Belgian Upper Paleocene: palaeoenvironmental implications. Review of Palaeobotany and Palynology, 104, 299-307. Gerrienne, P., Meyer-Berthaud, B., Fairon-Demaret, M., Streel, M. & Steemans, P., 2004. Runcaria, a Middle Devonian Seed Plant Precursor. Science, 306, 856-858.