Mangrove tree strength estimated with field experiments

Abstract

Mangrove forests protect coastal communities from wind and wave energy, including during extreme events such as cyclones and tsunamis. Under extreme conditions, energy absorption often exceeds mangrove tree strength, resulting in broken stems and uprooted trees. Such damage can restructure mangrove community composition and function for decades. Predicting the vulnerability of mangrove forests to damage from external forces is critical for understanding the likelihood of forest structural change during damaging events. Despite the importance of such predictions, we have little mechanistic understanding of mangrove tree strength. We measured mangrove strength across three root types (prop roots, pneumatophores, and buttress roots) using static pulling tests. We applied a non-destructive load to mangrove trees using a winch, and related the force applied to the bending induced in the tree. Mangroves were stronger than terrestrial trees, per unit tree size, and this scaled strength was similar across mangrove species of different root types. Un-scaled mangrove strength increased exponentially with tree size, towards a strength asymptote for the largest trees. Enhanced empirical knowledge of mangrove tree strength is critical to understand the coastal protection services provided by diverse mangrove forests, particularly in a future of global climate change and increased occurrence of extreme storms.