Trees in Himalayas losing foliage cover, say experts

Trees and plants in the Himalayas are losing their foliage cover due to global warming, which has aggravated since mid-1990s, conservationists have warned.

The effect of “browning” -- loss of canopy cover (opposite to greening) – is visible up to 4000 mt elevation in the Himalayas where the tree line ends. The browning would impact on lower level trees like oak, coniferous trees, Alpine scrubs such as juniper and rhododendron and even flowering plants at upper reaches.

However, the higher one goes up, browning or loss of foliage becomes less evident.

This was observed when researchers studied tropical mountains including the Himalayas using satellite images between 1982 and 2006. The satellite data gathered over a quarter of a century suggests greening was on the rise till 1995, when it nosedived sharply and showed no sign of return. The temperature was on the rise all along.

“Signatures of severe warming leading to moisture stress is visible in the Himalayas. It has a negative impact on vegetation,” Jagdish Krishnaswamy, senior fellow at Ashoka Trust for Research in Ecology and Environment, Bangalore and one of the coauthors of the study, told Deccan Herald.

Krishnaswamy along with colleagues from Indian Institute of Science Education and Research, Mohanpur in West Bengal and Centre for International Forestry Research in Indonesia looked at the vegetation cover of 47 higher elevation national parks all over the world to determine the health of tropical mountains that function as bell-weather of global warming. The mountains provide an opportunity to the scientists to pick up climate change signals more neatly.

“Temperature in the Himalayas has increased by 1.5 degrees between 1982 and 2006, which translates into 0.06 degree Celsius rise every year. Because of the temperature rise, flowering and bird migration pattern in the Himalayas too are changing,” said Robert John, an assistant professor at IISER.

Large scale ecological changes could have adverse effects for people living in the downstream, he said. Further ground based investigations are required to better understand the consequences.

The Himalayas may experience more rainfall in the future, but it would be seasonal. So even if total rainfall increases, there would be prolonged dry seasons leading to moisture stress and drought. Also winters in the Himalayas would be warmer.

The findings will appear in the journal Global Change Biology in November.