A satellite study of five mountainous tropical biodiversity hotspots around the globe, including tropical forests of the Himalayas, reveal that vegetation has been “browning” due to climate change.

Globally rising temperatures around the mid-1990s coincided with a decrease in foliage in key tropical mountain forests, indicating the loss of photosynthetic activity, says a research paper published in the journal Global Change Biology.

The Himalayas appear to have witnessed the highest temperature rise among the five regions, at around 1.5 degrees Celsius in the timeframe, finds the study which looked at 47 protected areas in South Asia, Southeast Asia, Africa, South America and Central America over the period 1982–2006.

‘75 p.c. vegetation hit’

“Our analysis shows that at least 75 per cent of vegetation in these forests have been impacted, and are producing less foliage than they used to before the mid-1990s,” said the lead of the paper, Jagdish Krishnaswamy, senior fellow at Ashoka Trust for Research in Ecology and the Environment in Bangalore.

“We can’t be sure why the 1990s appears to be a turning point, but we could hypothesise that this period saw a change in temperature and moisture regimes,” he added.

While the satellite study did not find corresponding changes in precipitation, it suggested that vegetation suffered from temperature-related “moisture-stress” that inhibited transpiration in flora.

The research paper cautions that “the decline of biodiversity in species-rich mountain ecosystems could have adverse impacts on ecosystem function and decrease ecosystem services on which millions of people are dependent.”

Mountain ecosystems, known to be particularly ecologically sensitive and vulnerable to climate change, should be placed in “high priority in global conservation strategies,” it adds.

Seasonal fluctuations

The scientists also observed an increase in seasonal fluctuations in temperature and rainfall over the period. The paper was co-authored by Robert John of the Indian Institute of Science Education and Research in Kolkata, and Shijo Joseph of the Center for International Forestry Research in Indonesia.

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