GUWAHATI, Oct 12 - Vast swathes of grasslands across the State�s four rhino habitats � Kaziranga, Manas, Orang and Pobitora � are undergoing large-scale degradation induced by invasive weeds and other forms of biotic pressures such as excessive cattle grazing. Matters stand worsened by the absence of scientific management of the grasslands that support wide-ranging wildlife, including the State�s flagship species, the rhino.
Conservationists are worried that unless urgent interventions are made, the developments could impact long-term sustainability of the existing rhino population.
�Invasive weeds and large-scale grazing of domestic livestock inside these protected rhino habitats have been a disturbing phenomenon. The damage to the grasslands and the resultant shrinkage has been considerable. Unless this trend is reversed through appropriate grassland management practices, irreparable harm can occur,� conservation biologist Dr Bibhuti Lahkar of Aaranyak, who has worked extensively in Manas National Park, said.
According to forest officials who served in these rhino habitats, the pressure of livestock grazing is visible in varied degrees in all the protected areas but the intrusion of invasive plants into grasslands is a bigger threat.
�Often it is poaching that hogs the limelight as the biggest threat to rhinos but the gradual intrusion of invasive species can cause more harm in the long run. These alien species are directly reducing the fodder for rhinos and other herbivores,� Mukul Tamuli, range officer of Pobitora said.
Terming the invasion by a Parthenium-like weed as �very serious�, Tamuli said that no solution was yet in sight as the weed was almost unstoppable and spreading to newer areas.
�Around five hectares of grassland has been affected by it so far. We are clueless how to deal with its spread, as even when those are uprooted and destroyed, new sprouts emerge quickly. We are now taking up the matter with experts. Another similar menace in the form of Ipomoea intrusion has, however, been tackled with some success. We are uprooting the plants and burning those,� he said.
Considering Pobitora�s small size and its even smaller grassland portion, the invasive weed can wreak havoc in the days ahead by drastically reducing the grassland. Already, one-third of its hundred-odd rhinos regularly move out of the sanctuary in search of food and the phenomenon can get worse due to more shrinkage of grassland.
As on today, half-a-dozen species of invasive plants are making inroads into rhino ranges across Assam, colonizing the grasslands in the process. Incidentally, these four protected forests shelter over two-thirds of the world�s one-horned rhino population.
The major invasive plants include Mimosa, Parthenium, Mikania, Chromolaena, Lantana, and Ipomoea. India�s Fifth National Report on Biological Diversity in 2014 identified these as invasive plant species responsible for harming local ecosystems.
Grassland ecosystems in both Kaziranga and Orang national parks have been enduring Mimosa invasion for years. In Kaziranga, the annual floods that inundate the park for a prolonged period have been acting as a natural check to the Mimosa menace.
In Orang, the situation has been disturbing and according to a 2011 study on land cover change in the park, the period from 1987 to 2008 saw Orang lose its wet alluvial grassland by 12.8 per cent, while dry savanna grassland and degraded grassland increased by 9.25 per cent and 6.51 per cent respectively � largely stemming from Mimosa invasion.