Life on the leading edge: Phenology and demography of the red mangrove Rhizophora mangle L. at the northern limit of its expanding range

Mangroves are expanding northward along the eastern coast of Florida and invading saltmarsh communities along the tributaries and main channels of rivers that flow into the Intracoastal Waterway system. To investigate R. mangle's demography, reproductive effort and survivorship of offspring were monitored for three years along the Matanzas River, northern Florida. Flowering was delayed, fruit production was year-round and hypocotyl production covered a longer period than for populations further south. If a propagule survived to the recruit stage, the individual was more likely to produce branches. In addition, if the propagule recruited in mud and in the low intertidal zone, then the individual was more likely to survive to the juvenile stage. Those propagules that eventually developed into juveniles had remained within one meter of the parent, had recruited in a vertical position and had larger hypocotyls. Two adults contributed 79% of the propagules that survived to the branched stage. These successful adults become the islands from which the population persists and expands along the leading edge of its distribution.