The plant was brought in as a cover and green manure crop in 1947, according to a 2023 review in the journal Plants . Now, the same review lists it as one of the 100 worst invasive species in the world. Giant mimosa arrived in Thailand with a simple job. The story is about how a farming fix can become a long-term headache for rivers, fields, and wildlife.
What happened to the birds
The review identifies several features that make giant mimosa a strong spreader. Cut plants tend to regrow from the stump. All this has serious implications for farmers. Thick clusters have led to a reduction in farmland and have also obstructed irrigation systems in the rice paddies and other croplands. That’s a lot of time and effort just to hold it back. The bird story is a bit more involved. The team also investigated what changes in the wetland correlated with these trends. Large waders were less abundant in giant mimosa-infested areas. There were other things as well. In deeper water, there were fewer small wading birds, and in a group called vegetation gleaners, there were fewer birds with increasing human settlement. Control isn’t easy. But the plant often grows back from parts left behind, and dormant seeds still sprout. In Australia , the release of natural enemies from the plant’s native range has been beneficial, but the review notes that biological control alone did not provide adequate control. This implies that a combination of several methods may be more effective than a single method. The takeaway is a cautious one. The evidence shows that this shrub is expensive, difficult to remove, and causes losses to farmers and some wildlife.
It can reach reproductive maturity within six to eight months and is estimated to produce up to 220,000 seeds per plant annually. Some seeds have been found to remain dormant in the soil for as long as 26 years. Moreover, farmers in the Mekong floodplains spend about 11 days per hectare each year clearing the plant. A12-year study in Tropical Conservation Science tracked resident waterbirds from 2003 to 2014 at Bung Boraphet, the largest freshwater wetland in Thailand . Resident waterbird numbers overall went down by 27%, the researchers found. Ducks fell the most, down 56%. The study did not attribute the entire 27% drop to mimosa. In one example from Australia, it says that 109 seedlings per square meter were still coming up ten years after a stand was cleared.
Because the study was limited to a single wetland, its numbers should not be taken as Mekong-wide figures.
The review says herbicides are the main method, but cutting, bulldozing, and fire can also work.
