Juvenile mangrove growth is restricted by belowground competition with mature tree roots

Abstract

Mangroves provide important ecosystem services and are uniquely structured forests due to strong biotic and abiotic influences in their intertidal habitat. These challenging conditions often create above- and belowground resource limitations which can interact to suppress juvenile growth resulting in an understory dominated by supressed juveniles. Though the response of juvenile mangrove growth to experimental release from aboveground resource limitations has been tested, less is known about the effect of belowground competition with mature tree root systems on juvenile growth. We experimentally released juvenile mangroves from mature tree belowground competition by repeated soil cutting treatments over 52 weeks. When belowground competition was reduced and thus belowground resource limitations relaxed, juvenile mangroves grew taller. Undisturbed control juveniles did not grow, though they had similar survival probabilities as treated juveniles across our sampling year. We demonstrated that release from belowground resource limitations was sufficient to restart growth of understorey juvenile mangroves, even when mature tree aboveground competition remained. This result enhances our understanding of species distribution and forest maintenance in this unique and important coastal ecosystem.