The Role of Soil Nutrients in Boundaries between Mangrove and Herbaceous Assemblages in a Tropical Estuary

We aimed to determine the role of soil nutrients in the herbaceous‐tree boundary in a tropical mangrove forest. We assembled plots in this boundary such that each was initially covered by ~50% of each life form. We added NPK to three of the plots monthly and monitored them, along with the control plots, for 18 mo. In plots with added NPK, mangrove branches grew over and shaded the herbaceous plants, resulting in the presence of mostly bare soil. The mangrove trees eventually covered ~80% of the experimental plots, but the proportion of cover in the control plots remained unaltered. We conclude that soil nutrient level modulates the mangrove‐herbaceous plant interaction in steps, and from a given level there is a shift in the dominant life form. This mechanism leads to a sharp transition over a smooth nutritional gradient.