Transient vegetation dynamics in a tropical coastal wetland: Sea‐level rise, glycophyte retreat, and incipient loss in plant diversity

• Published in: Journal of vegetation science Vol. 35; no. 3
• Main Authors: Ross, Michael S., Stoffella, Susana L., Ruiz, Pablo L., Subedi, Suresh C., Meeder, John F., Sah, Jay P., Vidales, Rosario, Minchin, Peter R., Scinto, Leonard J., Zhang, Keqi
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.05.2024
• Subjects: coastal tropical wetland transient vegetation dynamics; Coastal zone; Community structure; Composition; Encroachment; Environmental restoration; Florida's Southeast Saline Everglades, USA; glycophyte retreat; Halophytes; halophytes encroachment; incipient loss in plant diversity; Landscape; Leading edges; Mangrove swamps; Mangroves; mangroves and associates' transgression; Plant diversity; Population decline; Population growth; Restoration; sea‐level rise; Trailing edges; Transition zone; Vegetation; Vegetation changes; wetland restoration through freshwater delivery; Wetlands; Everglades
• ISSN: 1100-9233; 1654-1103
• DOI: 10.1111/jvs.13267

Aim and Questions Sea‐level rise has been responsible for extensive vegetation changes in coastal areas worldwide. The intent of our study was to analyze vegetation dynamics of a South Florida coastal watershed within an explicit spatiotemporal framework that might aid in projecting the landscape's future response to restoration efforts. We also asked whether recent transgression by mangroves and other halophytes has resulted in reduced plant diversity at local or subregional scales. Location Florida’'s Southeast Saline Everglades, USA. Methods We selected 26 locations, representing a transition zone between sawgrass marsh and mangrove swamp, that was last sampled floristically in 1995. Within this transition zone, leading‐ and trailing‐edge subzones were defined based on plant composition in 1995. Fifty‐two site × time combinations were classified and then ordinated to examine vegetation–environment relationships using 2016 environmental data. We calculated alpha‐diversity using Hill numbers or Shannon–Weiner index species equivalents and compared these across the two surveys. We used a multiplicative diversity partition to determine beta‐diversity from landscape‐scale (gamma) diversity in the entire dataset or in each subzone. Results Mangrove and mangrove associates became more important in both subzones: through colonization and establishment in the leading edge, and through population growth combined with the decline of freshwater species in the trailing edge. Alpha‐diversity increased significantly in the leading edge and decreased nominally in the trailing edge, while beta‐diversity declined slightly in both subzones as well as across the study area. Conclusions Recent halophyte encroachment in the Southeast Saline Everglades continues a trend evident for almost a century. While salinity is an important environmental driver, species’ responses suggest that restoration efforts based on supplementing freshwater delivery will not reverse a trend that depends on multiple interacting factors. Sea‐level‐rise‐driven taxonomic homogenization in coastal wetland communities develops slowly, lagging niche‐based changes in community structure and composition. Our study documented the transgression of mangroves into freshwater marshes in South Florida coastal wetlands, continuing a trend evident for nearly a century. Salinity is a key driver, but species’ responses indicate that freshwater supplementation will not reverse this complex trajectory. Sea‐level rise leads to slow taxonomic homogenization in coastal wetlands, which lags changes in community structure and composition.