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ABSTRACT Sea level rise and storm surges affect coastal forests along low‐lying shorelines. Salinization and flooding kill trees and favour the encroachment of salt‐tolerant marsh vegetation. The hydrology of this ecological transition is complex and requires a multidisciplinary approach. Sea level rise (press) and storms (pulses) act on different timescales, affecting the forest vegetation in different ways. Salinization can occur either by vertical infiltration during flooding or from the aquifer driven by tides and sea level rise. Here, we detail the ecohydrological processes acting in the critical zone of retreating coastal forests. An increase in sea level has a three‐pronged effect on flooding and salinization: It raises the maximum elevation of storm surges, shifts the freshwater‐saltwater interface inland, and elevates the water table, leading to surface flooding from below. Trees can modify their root systems and local soil hydrology to better withstand salinization. Hydrological stress from intermittent storm surges inhibits tree growth, as evidenced by tree ring analysis. Tree rings also reveal a lag between the time when tree growth significantly slows and when the tree ultimately dies. Tree dieback reduces transpiration, retaining more water in the soil and creating conditions more favourable for flooding. Sedimentation from storm waters combined to organic matter decomposition can change the landscape, affecting flooding and runoff. Our results indicate that only a multidisciplinary approach can fully capture the ecohydrology of retreating forests in a period of accelerated sea level rise. 

Abstract. Sea-level rise, saltwater intrusion, and wave erosion threaten coastal marshes, but the influence of salinity on marsh erodibility remains poorly understood. We measured the shear strength of marsh soils along a salinity and biodiversity gradient in the York River estuary in Virginia to assess the direct and indirect impacts of salinity on potential marsh erodibility. We found that soil shear strength was higher in monospecific salt marshes (5–36 kPa) than in biodiverse freshwater marshes (4–8 kPa), likely driven by differences in belowground biomass. However, we also found that shear strength at the marsh edge was controlled by sediment characteristics, rather than vegetation or salinity, suggesting that inherent relationships may be obscured in more dynamic environments. Our results indicate that York River freshwater marsh soils are weaker than salt marsh soils, and suggest that salinization of these freshwater marshesmay lead to simultaneous losses in biodiversity and erodibility. 

Abstract The impacts of climate change on ecosystems are manifested in how organisms respond to episodic and continuous stressors. The conversion of coastal forests to salt marshes represents a prominent example of ecosystem state change, driven by the continuous stress of sea‐level rise (press), and episodic storms (pulse). Here, we measured the rooting dimension and fall direction of 143 windthrown eastern red cedar (Juniperus virginiana) trees in a rapidly retreating coastal forest in Chesapeake Bay (USA). We found that tree roots were distributed asymmetrically away from the leading edge of soil salinization and towards freshwater sources. The length, number, and circumference of roots were consistently higher in the upslope direction than downslope direction, suggesting an active morphological adaptation to sea‐level rise and salinity stress. Windthrown trees consistently fell in the upslope direction regardless of aspect and prevailing wind direction, suggesting that asymmetric rooting destabilized standing trees, and reduced their ability to withstand high winds. Together, these observations help explain curious observations of coastal forest resilience, and highlight an interesting nonadditive response to climate change, where adaptation to press stressors increases vulnerability to pulse stressors.