This non-native invasive plant is familiar to many Southeast Asian farmers, having cloaked wetlands from Myanmar to Vietnam. Even more common are the thick carpets of water hyacinth, another highly invasive plant from the Americas, that cover much of the region\u2019s lakes and marshes.<\/p>\n\n\n\n
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<\/div>An invasive species is a plant or animal that is reproducing in the wild in an area where it is not native, having been introduced as a result of human activity, and which has a negative impact on native species and ecosystems.<\/p>\n\n\n\n
Not all introduced species become invasive, but invasive species can be a major driver of habitat change, biodiversity loss and species extinction.<\/p>\n<\/div><\/div><\/div>\n\n\n\n
Invasive plants threaten the Mekong\u2019s biodiversity<\/h2>\n\n\n\n
The Mekong\u2019s freshwater and terrestrial ecosystems span a vast transnational basin at the heart of the Indo-Burma biodiversity hotspot. The wetlands<\/a> of the Mekong floodplains are known to support some of the greatest congregations of large waterbirds in Southeast Asia. Much of these once-biodiverse Mekong floodplains is now cultivated, and the few remaining areas of natural wetland and seasonally flooded grassland are under threat from encroachment, grazing and fires to clear land for agriculture.<\/p>\n\n\n\n A major, and perhaps far subtler, driver of ecological change is non-native invasive species. The resilience of remaining areas of floodplain wetlands is constantly tested by invasive aquatic plants, such as water hyacinth and giant mimosa. Dryer areas have been invaded by the fast-spreading river tamarind, a species native to Central America that is often planted as a quick reforestation fix and to provide fodder for animals.<\/p>\n\n\n\n There has been little research on the impacts of invasive plants on wetland ecosystems in Southeast Asia, even though their extent has been well documented at many landscapes, and management and control initiatives are already well in place at several sites.<\/p>\n\n\n\n Did you know…<\/p> Globally, invasive species have been\u00a0identified<\/a>\u00a0as one of the top five drivers of biodiversity loss<\/p><\/div><\/div>\n\n\n\n Plants like giant mimosa and water hyacinth often outcompete<\/a> native plant assemblages and have the potential to deprive native species, such as the globally threatened Bengal florican, of key areas of remaining habitat, as they alter the environment species have evolved to thrive in. A 2018 study<\/a> showed that the nesting success of river terns on sandbanks along the Cambodian stretch of the Mekong was lower in areas with high cover of giant mimosa, with chick survival rate decreasing with vegetation height. It is probably safe to assume this problem afflicts other species that use open areas of sandy riparian banks for nesting, such as plovers.<\/p>\n\n\n\n Mimosa pigra <\/em>is widely thought to have arrived in the Lower Mekong river basin at some point between the 1950s and the 1980s. Today, it covers areas in impenetrable thickets where few other species can grow. The plant spreads quickly because it produces large quantities of seeds that are dispersed by floodwaters during the monsoons, and now covers substantial portions<\/a> of the Tonle Sap floodplain in Cambodia. In Laos\u2019s well-studied Xe Champhone wetlands, there are similarly large areas<\/a> covered by water hyacinth and giant mimosa. At one point, over 3,000 hectares<\/a> of wetlands in Vietnam\u2019s Tram Chim National Park, a site well known for its Sarus crane populations, had been smothered by mimosa.<\/p>\n\n\n\n Mimosa stands can directly threaten the biodiversity of seasonally inundated grasslands and freshwater marshes by outcompeting native shrubs and altering habitat for wildlife. A small number of species may be able to benefit from the habitat created by dense stands but there are also impacts for farming: giant mimosa spreads quickly into paddy areas and is not very palatable to livestock. It also chokes the irrigation systems that supply rice fields.<\/p>\n\n\n\n In one study<\/a> in Kratie province, eastern Cambodia, farmers reported that they had to spend 11 days per hectare every year clearing stands of giant mimosa from their paddy fields. Farmers often lack the resources needed to address the problem on a long-term basis. Fishers around the Tonle Sap also suffer significant losses<\/a> in income as a direct result of giant mimosa invasions.<\/p>\n\n\n\n As well as being one of the largest areas of seasonally inundated floodplain wetlands in the Cambodian Mekong delta, the Boeung Prek Lapouv Management and Conservation Area is a Sarus crane reserve. The wetland is estimated to support up to 35% of the regional population of Sarus cranes, a threatened species on the brink of extinction in mainland Southeast Asia, and very large congregations of the critically endangered yellow-breasted bunting. When drawing up a management plan in 2013, local people and site managers acknowledged the long-term threat posed by the giant mimosa.<\/p>\n\n\n\nCost-effective solutions to giant mimosa<\/h2>\n\n\n\n
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