Understanding Grenada’s mangroves: zonation, plasticity, and the potential for restoration
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The white mangrove (Laguncularia racemosa) is widely distributed throughout both the Caribbean region and the mangrove ecosystems (mangals) it inhabits, despite being considered restricted to the landward fringes of the forest (i.e., the back mangal). In Grenada, it has been observed expressing various forms of phenotypic plasticity, including aerial root expression, prompting questions about the link between its plasticity and mangrove community zonation. I hypothesized that mangal zonation and white mangrove plasticity were influenced by both site-level (forest type) and plot-level factors (edaphology and hydrology), and that plasticity also contributed to the zonation observed through niche expansion. I conducted vegetation surveys at one basin forest and one fringe forest in Grenada in summer 2020–2021, collecting environmental (site characteristics and soil chemistry) and vegetation data (tree height and size, aerial root presence, leaf size and thickness). I also surveyed white mangroves at nine additional sites across three islands in the country to further document the extent of white mangrove plasticity. Overall, the species was more structurally important (i.e., had a higher relative density and dominance) than both red and black mangroves and was well-distributed in all zones except the fringe forest’s seaward zone. White mangroves showed preference for higher-elevation habitat with a limited hydroperiod, including the seaward zone of the basin forest, revealing that their distribution is driven by elevation and not zone per se. White mangroves exhibited trait plasticity in tree height, diameter, leaf size, and root form in response to salinity and elevation. Plasticity in root form was most interesting, as white mangroves produced pneumatophores in shallow water and adventitious roots in deeper water, allowing the species to survive in varying water depths and defy expected zonation patterns. The link between these two concepts should be explored in other forest ecosystems to further understand the effects of intraspecific variation and plasticity on community structure and zonation. These findings can also help improve mangrove restoration planning in the Caribbean by highlighting the versatility of the white mangrove. Incorporating the species into a multi-species approach can improve the success rates, cost-effectiveness, and sustainability of restoration in the region.