Plant invasion in mangrove forests worldwide

Plant invasion is a major threat to natural ecosystems, and mangrove forests are among the most threatened ecosystems in the world. However, since mangrove species primarily occur in the saline and intertidal environment that is inhospitable for most terrestrial and freshwater plants, it is commonly assumed that mangrove forests are resilient to plant invasion. Still, many salt tolerant aquatic and terrestrial plants as well as epiphytes are found to invade the mangrove forests, and we know little about those invasive plants, their functional traits, invasion patterns and pathways and their ecological consequences. In a survey of global literature, we found a total of 57 plants reportedly invasive in the world's mangrove forests. These plants possessed the traits of salinity tolerance, tolerance to anaerobic condition, high fecundity and rapid growth. About 19% of invasive plants were anthropogenically introduced for coastal land stabilization, and the rests were accidental introduction. Invaders were found to colonize along the forest edges or forest interior, but mostly in the raised lands. That is, the presence of diversified microhabitats such as raised land and intertidal mudflat might help both halophytic and non-halophytic plants to invade the mangrove forests. Some invaders (30%) were transient, but many (70%) could persist for a longer time; and these species could modify habitat conditions, impede natural regeneration of mangroves and disrupt their faunal assemblage. Together, plant invasion in mangrove forests is much more widespread and problematic than commonly perceived, underscoring the need for the integration of invasive plant management strategy into mangrove forest management.