Search for: All records

Naturally formed forest patches known as tree islands are found within lower-statured wetland matrices throughout the world, where they contrast sharply with the surrounding vegetation. In some coastal wetlands they are embedded in former freshwater marshes that are currently exposed to saltwater intrusion and mangrove encroachment associated with accelerating sea-level rise. In this study we resurveyed tree composition and determined environmental conditions in tree islands of the coastal Florida Everglades that had been examined two decades earlier. We asked whether tree islands in this coastal transition zone were differentiated geomorphologically as well as compositionally, and whether favorable geomorphology enabled coastal forest type(s) to maintain their compositional integrity against rising seas. Patterns of variation in geomorphology and soils among forest types were evident, but were dwarfed by differences between forest and adjacent wetlands. Tree island surfaces were elevated by 12–44 cm, and 210Pb analyses indicated that their current rates of vertical accretion were more rapid than those of surrounding ecosystems. Tree island soils were deeper and more phosphorus-rich than in the adjoining matrix. Salinity decreased interiorward in both tree island and marsh, but porewater was fresher in forest than marsh in Mixed Swamp Forest, midway along the coastal gradient where tropical hardwoods were most abundant. Little decrease in the abundance of tropical hardwood species nor increase in halophytes was observed during the study period. Our data suggest that geomorphological differences between organic tree island and marl marsh, perhaps driven by groundwater upwelling through more transmissive tree island soils, contributed to the forests’ compositional stability, though this stasis may be short-lived despite management efforts. 

Abstract Degradation of wetland ecosystems results from loss of hydrologic connectivity, nutrient enrichment, and altered fire regimes, among other factors. It is uncertain how drivers of wetland ecosystem processes and wetland vegetation communities interact in reversing the ecological trajectory from degraded to restored conditions. We analyzed biogeochemical and vegetation data collected in wetlands of the Florida Everglades at the start of (2015) and during (2018 and 2021) the initial stages of rehydration. Our objectives were to analyze the allocation of carbon and nutrients among ecosystem compartments and correlated trajectories of vegetation community change following rehydration, to identify the drivers of change, including fire, and analyze macrophyte species‐specific responses to drivers. We expected to see changes in vegetation toward more hydric communities that would differ based on wetland baseline conditions and the magnitude of the hydrologic change. During the study period, both length of inundation and surface water depth increased throughout wetlands in the region, and four fires occurred, which affected 51% of the sampling locations. We observed biogeochemical shifts in the wetland landscape, driven by both hydrology and fire. Total phosphorus concentrations in soil and flocculent detrital material decreased, while soil carbon:phosphorus and nitrogen:phosphorus mass ratios increased at sites further away from water management infrastructure. Transitions in vegetation communities were driven by an increase in hydroperiods and by the distinct changes in nutrient concentrations or soil stoichiometric ratios in each subregion. The abundance of macrophyte species typical of short‐hydroperiod prairies strongly decreased, while dominant long‐hydroperiod species, such asEleocharis cellulosa, expanded. Fire facilitated the expansion of thickly vegetated plumes of invasiveTyphaat sites close to the water inflow sources. Overall, restored hydrology shifted vegetation community composition toward higher abundance of long‐hydroperiod species within six years. In contrast, removal of invasive vegetation controlled by soil phosphorus concentrations will likely require long‐term and interactive restoration strategies.