Vegetation recovery on neighboring tidal flats forms an Achilles' heel of saltmarsh resilience to sea level rise

Abstract

Coastal wetlands such as saltmarshes are valued as prominent buffering ecosystems to global climate change and sea level rise (SLR), yet their long‐term persistence may also be threatened by these global change stressors. While saltmarshes are increasingly thought to be resilient to SLR owing to high vertical marsh adaptability, their long‐term stability remains uncertain due to our poor understanding of marsh resilience at the marsh‐tidal flat interface, where wave disturbance can progressively shift vegetated marsh toward a bare tidal flat state. Here, we explore how SLR affects vegetation recoverability on tidal flats using cordgrass, a globally common saltmarsh foundation species, as a model plant. Combined field and model results demonstrate that small increases in wave forcing due to raised water depth over tidal flats can dramatically weaken or even block vegetation recovery from eroding marsh edges, through hampering seed persistence. Vegetation recovery on tidal flats next to the marsh edge thus represents an unrecognized Achilles' heel of marsh resilience to SLR, which if ignored may cause underestimation of marsh vulnerability. These findings are highly relevant for a more comprehensive assessment of marsh susceptibility to SLR in systems where seeds play an essential role in revegetation of tidal flats, and highlight the importance of maintaining either a wave‐protected or well‐elevated tidal flat near the marsh edge that allows for quick vegetation recovery for supporting resilient marshes.

Elevated micro-topography boosts growth rates in Salicornia procumbens by amplifying a tidally driven oxygen pump: implications for natural recruitment and restoration

“…Today, the rapidly growing human impact on natural systems is increasingly infringing upon and degrading the functioning and total area of ecosystems globally (Lotze et al, 2006). The capacity for pioneer species to recolonize de-vegetated landscapes is central to reversing the process of degradation and the loss of their environmental services (Zhu et al, 2019). However, the time scale over which re-colonization occurs varies dramatically between ecosystems.…”

Spatial and temporal patterns of initial plant establishment in salt marsh communities

“…Establishment, resilience and long‐term stability of salt marshes is, therefore, highly dependent on the species' abilities to re‐colonise and establish after disturbances at different scales. Understanding the species‐specific dispersal and re‐colonisation pattern is therefore important to conserve salt marsh biodiversity but also for the provision of regulatory ecosystem services such as coastal protection (Temmerman et al ., 2013; Möller et al ., 2014; Zhu et al ., 2019).…”

Burrowing crabs and physical factors hasten marsh recovery at panne edges

“…We also found that local increases in elevation at our marker rods correlated with panne recovery. Some studies have indicated that sea-level rise will increase the rate of panne formation, expansion, and coalescence, further contributing to marsh loss [24,50], while others suggest that poor drainage, insufficient accretion, and poor creek connectivity explain panne formation [47]. In our study we show that elevation, drainage, and inundation are inextricably linked and predictive of panne dynamics.…”

“…and colleagues called pannes the "unrecognized Achilles' heel of marsh resilience to sea-level rise"[50]. Much marsh degradation results from panne formation and expansion, but the mechanisms behind panne dynamics are not broadly understood.…”