An example of accelerated changes in current and future ecosystem trajectories: Unexpected rapid transitions in salt marsh vegetation forced by sea level rise

• Published in: Environmental challenges (Amsterdam, Netherlands) Netherlands), 2024-01, Vol.14, p.100842, Article 100842
• Main Authors: Valiela, Ivan, Lloret, Javier, Chenoweth, Kelsey, Wang, Yuyang
• Format: Article
• Language: English
• Subjects: Accretion; Great Sippewissett Marsh; Invasive species; Nitrogen supply; Salt marsh; Sea level rise
• ISSN: 2667-0100; 2667-0100
• DOI: 10.1016/j.envc.2024.100842

•Great Sippewissett Marsh vegetation has increasingly been altered in recent years.•Sea level rise is promoting conversion of short to taller Spartina alterniflora.•Plant changes are promoting creek bank slumping, wrack strandings and habitat loss.•Models predict sea level rise will lead to submergence of the entire marsh.•Phragmites australis invasion is replacing species and preventing marsh migration. Accelerated sea level rise has forced greater changes in the vegetation of Great Sippewissett Marsh during the recent few years than were recorded in the previous half century. Even with conservative estimates of sea level rise, accretion in the salt marsh platform would be insufficient to match submergence, but in addition, a new set of cascading changes seem to be accelerating the transformation of the Great Sippewissett Marsh vegetation mosaic, including conversion of cover by short to taller Spartina alterniflora, leading to lowering below-ground biomass and weakening of sediment columns, while the greater above-ground biomass increases wrack that strands and smothers high marsh vegetation. In addition, a salt-tolerant variant of Phragmites australis has begun to aggressively invade upper elevations of Great Sippewissett Marsh, replacing high marsh species cover, as well as dominating adjoining low-lying areas that might have allowed salt marsh landward migration as sea level effects increase. In many parts of Great Sippewissett Marsh, area of high marsh is steadily diminishing, taller S. alterniflora has extended upwards in areas previously supporting high marsh species, but its landward progress is now impeded by competition and shading by the phalanx of P. australis that has extended down-slope. The vegetation gradient in Great Sippewissett Marsh—and other salt marshes—is in rapid transition, and its decadal future seems in doubt. [Display omitted]