A Model of the Success of Mangrove Colonization at its Northeastern Boundary in Florida (USA) and Persistence in the Face of Rising Sea Level

An adaptation of the Marsh Equilibrium Model (MEM) for simulations of mangrove (Avicennia germinans) colonization of marsh habitat at their northern boundary indicates that the success of colonists depends on the relative elevation of the site, future acceleration of sea-level rise (SLR), and growth strategy. On low elevation sites it is a race against time for young mangroves. Their success depends on their ability to 'out-grow' the rise in sea level through biogenic accretion. Counterintuitively, mature mangroves at a similar elevation may not survive as long as young mangroves, because mature mangroves do not possess the same growth advantage. Moreover, the survival of mangroves is dependent on their growth strategies with respect to their vertical distributions. Several growth strategies are possible: They can have a fixed vertical range (within the tidal frame) throughout their development, or they can have an expanding range. The most successful strategy is one in which the vertical growth range expands to lower elevations as the mangroves mature. This strategy survives more than a century following a 100 cm of sea-level rise/century . Simulations of the fate of mature mangroves show reduced survivorship, vertical accretion, and carbon sequestration. Mangroves with expanding vertical ranges appear to be superior to salt marshes in their ability to keep up with sea level. Mangroves produce tissue with higher lignin concentrations than Spartina alternifora and have higher biomass production. Consequently, mangroves are superior contributors to the biogenic component of marsh surface accretion. In terms of coastal resilience, the climate-driven, northward migration of mangroves may be beneficial for Florida wetlands. With respect to northern migration it is a race against time. Marshlands may drown before mangroves can colonize.