Cambodia faces alien threat

Photo by: HENG CHIVOAN
Cambodia’s alien invader - the mimosa pigra, or giant mimosa, a thorny plant originally from the Amazon jungle - growing by a roadside in Phnom Penh’s Russey Keo district.

ORIGINS IN SE ASIA
The giant mimosa and its seeds probably floated down the rivers from Thailand in the 1980s, according to Robert van Zalinge at WCS, meaning the plant is not Vietnamese as its colloquial Cambodian name would suggest.

The Phnom Penh Post
http://www.phnompenhpost.com/

Written by Christopher Shay and Khouth Sophak Chakrya
Monday, 20 April 2009

An invasive plant species from the Amazon jungle is threatening Cambodia's biodiversity as well as costing farmers and fishermen lots of time and money

AN alien has invaded Cambodia and taken over large swaths of land, threatening the Kingdom's ecosystem, and it appears the uninvited guest is here to stay.

The alien threat is the mimosa pigra, or giant mimosa, a thorny plant originally from the Amazon jungle that is out-competing Cambodia's indigenous plants and putting the country's biodiversity at risk. It is also costing Cambodian farmers and fishermen time and money.

"It's a very strong, hardy plant. It can tolerate flooding, and it can tolerate dry [conditions]," Robert van Zalinge at the Wildlife Conservation Society (WCS) said.

Taking over flooded plains that have been cleared of natural vegetation, the giant mimosa forms dense, homogenous stands, says Chai-Aing Sopharith, the ecotourist manager at Osmose, an NGO that operates around the Tonle Sap.

Neou Bonheur, the deputy secretary general at the Tonle Sap Basin Authority, said that though studies have tended to be small, it's clear the giant mimosa problem has spread across the entire Kingdom.

Despite the threat, Long Kheng, the core area director of the Tonle Sap Conservation Project, said that at the moment, "we don't have any program to control the invasive species".

The alien plant has made only small incursions into the most biologically diverse areas around the lake, but according to Long Kheng, it still poses a serious ecological threat.

"If we don't take action, the mimosa pigra will destroy the ecosystem of the area," he said.

The rapacious plant threatens 20 percent of the Tonle Sap flood area - a "huge area", said Zalinge.

The plant has already become the bane of Cambodian farmers, who spend money and labour clearing their plots of the plant.

Srey Kong Bunna, 37, a farmer from Phsa Krom in Kampong Chhnang, said that he regularly chopped down the plant and even tried burning the plants down, but nothing has stopped it from reappearing.

"I pay at least 100,000 riels (US$25) every year to clear the giant mimosa from my small rice crop," Srey Kong Bunna said.

The giant mimosa can survive floods and fires, and can grow back from its root system, said Neou Bonheur.

It's not just the farmers who worry about the giant mimosa infestation. Fishermen fear the plant as well.

"We worry that we won't be able to catch fish in the future because the giant mimosa grows in our lake," Srey Kong Bunna said, adding that fish refuse to spawn in areas with a giant mimosa infestation.

There have been no comprehensive studies on the economic effects of the plant on Cambodia's fish stock, but fishermen, conservation groups and scientists agree the plant has a serious negative impact.

"You can imagine that vast homogenous stands - especially of a thorny species that doesn't provide much food - will be avoided by fish," said Zalinge.

There are a few ways to combat an invasive species, but they all take money and political will - both things the Kingdom is lacking at the moment, Zalinge said.

In Australia, biocontrol - the introduction of a predator of the invasive species - has been used against the giant mimosa with some success, but the initial costs required to ensure that the new alien pest will not also damage the ecosystem are very high. But as Zalinge points out, "It's a lot of work initially but once it's released, it works for free."

Manual removal has also been used effectively in Vietnam in small areas, and the WCS recommends this technique for the Tonle Sap core area where the infestation is still scattered.

There is also a Minnesota-based chemical company, MSK International Chemical, started by a Cambodian refugee, that claims to have a comprehensive plan to deal with the giant mimosa in Cambodia.

The active ingredient of the company's chemical, triclopyr - approved by the US Environmental Protection Agency for use in aquatic areas - "does not affect human health", according to Darith Sokchan, the deputy director of Mincam Cambodia, the company that imports the chemical from the US.

By using aerial photography and mapping software to prioritise treatment combined with proper training of sprayers, MSK Chemical thinks it can control the plant.

But Zalinge at WCS stressed that the most effective way of slowing the plant's spread was to protect the natural vegetation in sensitive areas and says that if native species are replanted after the giant mimosa has been removed, then perhaps they could better compete with the invasive mimosa.

With a combination of techniques to battle the invader, Preap Visarto, the deputy director of plant protection at the Ministry of Agriculture, Forestry and Fisheries, said Cambodia could become a more productive nation, liberating its farms and fisheries from the menace. But, he said, the Kingdom simply does not have the funds.

And if the money does not arrive, Zalinge predicted that "the worst is still to come".