Biogeography, threats and phylogenetic structure of mangrove forest globally and in South Africa: A review

Abstract

Mangrove forests provide enormous goods and services. However, the future of the forests has been questioned at many occasions. In response, much attention has been given to the ecology and biology of mangroves with little information, if any, on the phylogenetic structure of mangrove forests despite recent multiple calls for prioritizing conservation actions based on phylogenetic information. In this study, we firstly review briefly the ecology of mangrove forests and secondly review our current knowledge of the phylogenetic structure of the forests. On a global scale, there is a match between biogeographic regions experiencing species decline and the distribution ranges of highly evolutionary distinct species, thus raising concern and providing ways of prioritizing actions. At the regional scale, mangrove communities (as evidenced by the net relatedness index) are phylogenetically patterned such that closely related species occur more often than expected by chance, perhaps indicative of recent in situ diversification. This is also a concern as pests and pathogen attacks tend to spread rapidly among closely related species. However, there is a trend toward a phylogenetic overdispersion when moving eastward. Nonetheless, the patterns described at regional scale may not always match those of local scale, but knowledge of mangrove phylogenetic structure at local scale is scant. For example in South Africa, the impact of human activities on the phylogenetic structure of mangrove communities is unknown. We conclude with a call for more research at a local scale, particularly in South Africa, to elucidate how mangrove forest is phylogenetically restructured in response to anthropogenic disturbances, and how phylogenetic information can inform conservation, management and restoration of mangrove forests.