Laborers uprooting mimosa in Kaziranga

New Delhi : Imagine a nondescript weed posing as a threat to one of the world’s important biodiversity hot spots. “Silent Stranglers”, is a report that documents the threats of this weed called mimosa to the habitat of Kaziranga National Park . It also records three years of relentless efforts to eradicate this menace by the wildlife Trust of India (WTI) and the Assam Forest Department.

The report hopes to serve as a valuable reference for students and field biologists who would like to undertake such projects in the future. The mimosa eradication programme was conducted with support from International Fund for Animal Welfare (IFAW).

Two varieties of mimosa generally occur in KNP, Mimosa invisa (thorny variety) and Mimosa inermis (thornless variety). Mimosa growth strangulates the grass and other species in grasslands and as a result, the plants suffocate and die due to lack of photosynthesis. Mimosa is also found in the river bank and water logged areas, besides the usual grasslands. Mimosa seed can easily spread through rain or flood waters and by wind.

Mimosa is considered an invasive species in India . The plant is indigenous to central and south America . Being heliophytic, they do not grow under close canopies. They are generally found in the grassland areas of Kaziranga. Eastern alluvial grasses, such as Saccharum procerum, Saccharum spontanum, Arundo donax, Phragmites karka and Alpinia allughas are most common grass species of Kaziranga.

Dilip Deori, field officer of WTI supervising mimosa uprooting in Kaziranga National Park said, “Mimosa uprooting in KNP is carried out in two phases. The first phase starts in April till the end of June and the second phase from September till the end of December. Uprooting of mimosa is also carried out in a rotational manner. The first is during the seedling stage, when plants are removed before flowering and in the second stage, the germinated seedlings are removed.

Elephant foraging a grassland in Kaziranga

Mimosa is difficult to eradicate completely, there still remains a possibility that the uprooted areas may stage a comeback. Mimosa seeds may remain dormant for as long as five years and the germination capacity of the plant is also reportedly high.

In 2002-03, mimosa occurred in 2.13 sq km (0.5 % area) area of the KNP that also constitute some core areas of the park. All the four ranges of the KNP namely, Agaratuli, Kohora, Bagori and Burapahar are infested with mimosa in varying degrees. According to Deori, 130 hectares were cleared of mimosa last year and 72 hectares in the first phase of 2005. The second stage of the current year is due to begin by mid September.

About 70 to 80 casual workers were employed during the uprooting process. These laborers had to be stationed inside the forests for months together, as soon as the uprooting process began. Rations and other amenities were then provided by the forest department. The daily wages of the laborers were taken care of by WTI during both seasons.

Deori said that mimosa uprooting in Kaziranga involves constant threats from roaming predators and large herbivores of the park, such as rhinos, elephants, tiger, leopards and other wild animals. Other mega herbivores of the park include wild buffalo, swamp deer, wild boar and hog deer.

The uprooted mimosa is usually dried and burnt. However other methods were also experimented such as mulching and rotational uprooting. The quadrate method is used to find out the frequency, density and abundance of the species in a given area, to ascertain the success of the programme.

Deori said, “Mimosa can grow upto a height of seven meters and a single plant can cover upto 25 sq meters of the ground area. This requires a minimum of five workers over one hour”.

Mimosa growth in Kaziranga

“After uprooting in several mimosa infested areas in the last quarter, we have observed a secondary succession of new grasses forming a sub-sere (new foliage) layer in these areas” he adds further.

The mimosa eradication programme in Kaziranga will continue till the time mimosa is completely eradicated. As the wide variety of herbivores and mega-herbivores of the park depend on these grasslands, the survival of the native grasslands in Kaziranga is crucial to the quality of their habitats and plants they graze upon every day. Eradicating mimosa is crucial for securing the wild habitats from degradation.

The report on mimosa eradication has chronicled the mimosa infestation and the impact caused by it to the wild habitats of Kaziranga. The report is also an acknowledgement of the hard work of all the workers and officials that collectively put in to combat the invasive species.

Pix credit: Dilip Deori