'Mile-a-minute' weed threatens Nepal's jungles

But conservationists say the huge wildlife reserve is under threat from a foreign invader that is destroying its delicate eco-system, with potentially catastrophic implications for the animals that live there.

Over the past decade and a half, a non-native creeper dubbed "mile-a-minute" for its rampant growth has covered large swathes of the 932-square-kilometre (579-square-mile) park, a major tourist attraction and UNESCO world heritage site.

Biologist Naresh Subedi says the plant, micania micrantha, has already engulfed more than a third of prime rhino habitat in the national park, and believes the impact on wildlife could be devastating.

"Micania is ranked as one of the most invasive plants in the world," said Subedi, who works for the National Trust for Nature Conservation (NTNC) in Chitwan.

"It can smother, choke and pull over other plants, it causes soil erosion, and no single technique has yet proved effective for its long-term control.

"More than a third of the rhino habitat in Chitwan has now been covered to a greater or lesser degree, posing a serious threat to the population."

Although micania is edible, it is nutritionally deficient compared to the native grasses of Chitwan which can sustain "mega-herbivores" like rhinos which require a large, daily intake of nutrient-rich vegetation.

Native to South America, micania grows over the plants that make up the diet of the rhinos, blocking the sunlight they need to survive.

A single plant can produce between 20,000 and 40,000 seeds, which are dispersed by wind, and its shoots are reported to grow by up to 2.7 centimetres (about one inch) a day.

Micania is thought to have been introduced to South Asia during the second world war as a form of camouflage for military bunkers in India.

It was later used on Indian tea plantations to cover exposed strips of soil in an effort to prevent erosion, and was first reported in the east of neighbouring Nepal in 1966.