At present, just five percent of the 880-sq km Valmiki Tiger Reserve is under grasslands. The park management hopes more grassland will support more prey animals that will in turn support more tigers.

Limited grassland species in the park like ungulates, which are an important food source for tigers, have forced the management to do a rethink.

"This was one of the reasons why the park has a low density of tigers. My first priority after I joined the reserve last July was to create more grasslands," field director Santosh Tiwari told IANS.

Scattered population of sambar, nilgai, gaur, chittal, hog deer, langur and rhesus macaque, among others, as well as a few rhinoceros are also found in the reserve.

The Madanpur forest range is home to many herbivores because the rich alluvial soil enriched by the river Gandak has favoured the growth of grasses, Tiwari said.

Common grass in the reserve include imperata cylindrica, saccharum spontaneum and saccharum munja.

The forest department, in collaboration with the NGOs Wildlife Trust of India (WTI) and Germany's Nature and Biodiversity Conservation Union (NABU), is currently conducting a study to boost grasslands in the reserve.

Valmiki had more grasslands in the past. But they gradually turned into woodland due to lack of management. People also turned them into agricultural lands, said WTI manager Samir Kumar Sinha.

The forest was under the management of the Bihar State Forest Development Corporation before it became a tiger reserve in 1994.

Since it was a profit-making organisation, it introduced commercially important trees like teak, shisham and bamboo which turned the grassland and open areas into woodland, said Sinha.

Mixed forest vegetation is crucial for the herbivores as they are important sources of food. The availability of quality food boosts their breeding chances.

"The grass has became unpalatable for the herbivores due to ineffective management," Sinha told IANS.

Loss of grasslands led to a decrease in herbivore numbers, which reduced the tigers' food source.

The most robust statistical method for prey density estimation is Distance Sampling. But this technique requires at least 40 sightings of animals in an area. Valmiki has such a low herbivore base that this method was not possible, Sinha said.

Grassland and open areas were also invaded by unwanted species like mikenia, eupatorium and phoenix.

Recently, experts from the forest department, the Chitwan National Park in Nepal, WTI and NABU held a discussion on better management of grasslands.

They suggested experimenting with different methods before a suitable one could be implemented. They also recommended documenting the types of grasses in the park to understand their biology.

"We have already identified the sites to conduct the trial. We will introduce grasses that are locally available instead of bringing them from outside," Tiwari said.

Some 150 villages dot the periphery of the Valmiki Tiger Reserve. In addition, 25 revenue villages are in the Done Valley, a 45-sq km area in the heart of the reserve. Some 18,000 people live there.

Apart from human disturbances, poaching continues to be the biggest threat to the park.

The latest tiger census report released by the government in March last year estimated about 1,700 tigers. In 2008, it had put the numbers at about 1,400.

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