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Fast growth of Mimosa threatens Orang rhino habitat

Guwahati, Feb. 7: Authorities at the Rajiv Gandhi Orang National Park, who are already fighting a tough battle over straying rhinos, may now find it more difficult to combat the problem, with mimosa, an invasive species of plant, engulfing part of the habitat.

Satellite imageries from 1987-2008 have revealed that the wet alluvial grassland, which is an ideal habitat for the one-horned rhinoceros, has decreased by 10.09 square km because of the vigorous growth of mimosas.

Mimosa is a tropical American species, which was imported by tea planters from East Asia in the 1960s, as a nitrogen fixer prior to planting tea. It scrambles vigorously over other plants, forming dense tangled thickets up to 2 metres high and is commonly seen on the roadsides and in moist places.

Recently, a ranger of the park, Salim Ahmed, was injured when a rhino, which had strayed out of the park two days ago and crossed the Brahmaputra to Nagaon and Morigaon districts, traversing around 100km, attacked him.

This has been revealed now in a study done by Pranjit Kumar Sarma, a GIS expert with Aaranyak, on “Land cover change dynamics and future implication analysis in Rajiv Gandhi Orang National Park of Assam, using satellite data”.

In 1987, the area under wet alluvial grasslands was 30.63 square km. It decreased to 26.5 square km in 1999 and to 20.54 square km in 2008 while degraded grassland increased from 6.86 square km in 1987 to 10.35 in 1999 and 12 in 2008. There are 64 rhinos in the smallest national park in the state.

A study was carried out to observe the changes in land cover and its impact on rhino habitat in the national park, to understand the causes of land cover change in the park and to create baseline information on the condition of rhino habitat in the park.

Sarma told this correspondent that the area of moist alluvial grasslands would decrease further as no solution had been found to the mimosa problem.

“The study found that mimosa is the biggest threat to the Orang rhino habitat,” he said.

“In fact, it can invade the growth of other surrounding plants completely, which means habitat degradation and loss of biodiversity,” Sarma said.

The study has recommended immediate uprooting of invasive species like mimosa for conservation of rhino habitat in the park.

Another factor for decrease in rhino habitat has been deposition of silt from the Brahmaputra in the national park. Around 8 square km of the park is covered by silt while 0.94 square km area has been eroded by the river.

“Measures should be taken immediately to prevent grazing of cattle and encroachment in the park,” Sarma said.

He said the frontline staff often burnt the park’s grasslands unsystematically, without any scientific guidelines.

Wildlife managers are often ambivalent in their attitude towards fire and successive managers in one area develop different fire policies, he added.

The study recommends that proper ground survey should be done before burning the grasslands.

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