Measurement and Modeling of Above-Ground Root Systems as Attributes of Flow and Wave Attenuation Function of Mangroves

Mangrove forests protect the coasts from natural disasters such as storm surges and tsunamis. These ecosystems also deposit sediments—a key process in carbon sequestration and adapting to rising sea level. These services provided by mangroves are related to their drag effect that significantly attenuates flow and waves, and enhances sedimentation. The drag force exerted by mangroves is due to the complex structures of their above-ground roots. A key parameter for the quantitative assessment of drag force is the projected area of vegetation. In this chapter, we focus on the above-ground root system (prop roots) of Rhizophora—the most dominant genus in the Asia-Pacific region and likely to exhibit the highest drag among mangrove species—in exploring the projected area of vegetation. We describe the methods of field measurement and an empirical model for the projected area of the Rhizophora prop root system. The results show the allometric relationships between the prop root projected area and tree size, and how the allometric relationships vary depending on the sites. The developed model shows its great ability as well as some limitations in accurately predicting the projected area of prop roots. We then discuss the environmental factors that may affect the allometric relationship, and prospects in developing the universal model, which can predict the prop root projected area in any type of environment. We also discuss perspectives in the measurement and modeling of other types of mangrove above-ground root system such as pneumatophores of Avicennia and Sonneratia species.