By Sanjeeb Baruah, IANS
Guwahati : The mimosa plant, a toxic weed that is being used in Assam’s tea gardens to increase soil fertility, is posing a serious threat to mega herbivores like rhinoceroses and barking deer, particularly in the famed Kaziranga national park in northeastern India.
So much so that it is seen as a bigger danger to Kaziranga than poaching and floods. The park is home to around 1,700 one-horned rhinoceroses, the largest living population of the animal in the world today.
Endemic to tropical America, the mimosa was introduced by tea garden owners in the late 50s in Assam. The plant was used as a nitrogen fixer to improve soil quality for tea plantation.
However, it soon spread to other areas, invaded grasslands and strangulated native plant species and, as a result, restricted the supply of food for wild herbivores such as buffalo, rhinoceros and barking deer.
The problem is more acute in Kaziranga Park, as tea gardens adjoining the park are on a higher elevation and mimosa seedlings from the tea gardens easily get dispersed during floods in the park.
According to park director S.N. Buragohain: “Threats from the mimosa are bigger than poaching and floods, as they create a food shortage for the herbivores. For past few years, we have been uprooting them to get rid of the menace, but then lack of funds and limited manpower have delayed the process.
“Though funds are available for habitat restoration work in Kaziranga, they haven’t really trickled down to work budgets for mimosa eradication,” he added.
Dilip Deori of the NGO Wildlife Trust of India said: “We are facing a mammoth problem here as new areas are being infested by the mimosa every year.” He said the periphery of the park was at a greater risk.
“A road that passes through the periphery of the park has also increased the risk, as mimosa seeds that get stuck in the tyres of vehicles are carried to newer areas, which helped it spread quickly,” he said.
About 300 hectares in the Bagori, Kohora and Agratuli ranges of the park have been targeted for mimosa uprooting. “But we have to go back to the same area every year since they keep on sprouting from the soil.”
The problem is compounded by the fact that mimosa seeds remain dormant for more than three to four years and detection becomes very difficult.
Humid climatic conditions and the alluvial soil make the conditions favourable for the weed to germinate faster. These conditions are similar to some Latin American countries where these species have established large colonies.
The dense prickly thickets of the mimosa also obstruct free animal movement. Burning them results in mass regeneration. It spreads rapidly and suffocates native plant species.
Mimosa leaves are not palatable as they contain toxins such as hydroxyl and pyridone – non-protein amino acids harmful to animals.
“Since last year we have been using tractors for uprooting mimosa as they can cover more area at a minimum cost. But even then, we have to involve at least 60-70 labourers during each exercise,” said Deori.
“The cost involved is huge. The central government must provide the required resources so that the forest staff here can tackle the problem,” said Buragohain.
“For uprooting 30 hectares, we spent about Rs.200,000 last year. In the second phase, Rs.1.25 million was allocated by the NGO,” Deori said.
The Kaziranga park – traditionally covering an area of 429 sq km with another 429 sq km added now – was declared a World Heritage Site in 1985. A large variety of rare flora, fauna, and avi-fauna is also found here.
Already about 17 rhinoceroses are known to have been poached this year. The floods also displace hundreds of animals from the park annually.