YK Poudel

A study reveals that the treeline in the Dagala range has ascended by a staggering 221 metres in the last three decades.

This remarkable shift, from 4,291 metres above sea level (masl) in 1990 to 4,512 meters masl in 2020, underscores the impact of rising temperatures and changing precipitation patterns on the alpine ecosystem.

Presented at the PEER symposium, the study titled “Impact of climate change on alpine timberline and its socioeconomic impact on highlanders in Bhutan” not only highlights this dramatic ecological transformation but also draws attention to the critical socioeconomic repercussions faced by the country’s highland communities.

This shift is predominantly attributed to two key factors: temperature and precipitation. As the climate warms, the ecotone treeline in Bhutan is steadily moving to higher elevations, serving as a indicator of the impact of climate change.

A treeline represents the transition zone between lush, continuous forests and the onset of alpine grasslands or scrublands.

The Department of Forest and Park Services (DoFPS) conducted the study, which shows how the country’s treeline has experienced a substantial elevation change over the years.

In 1990, the mean elevation of the treeline stood at 3,806 masl, while in 2020, it had risen to 4,174 masl—an increase of 368 meters during the last three decades.

The investigation extended beyond the Dagala range, encompassing four other interior mountain regions in Bhutan. Notably, the Black mountain range, Bribdungla, and Merak-Sakteng all showed significant treeline shifts, underscoring the widespread nature of this ecological change.

Furthermore, the study uncovered an unprecedented alpine treeline ecotone at a staggering 5,300 metres, eclipsing previous records—previously, the highest treeline in the northern hemisphere was at 4,900 masl in southern Tibet and the highest treeline in the world was at 5,000 masl in the southern hemisphere in the Andes.

This alteration in the landscape is causing blue pine, typically confined to lower elevations, to encroach upon fir forests between 3,400 metres and the treeline.

Changa Tshering from DoFPS said that the study used Alpine Timberline Ecotone Indices (ATEI) to examine areas where forests cannot establish, including alpine meadows.

The research also delved into changes in land cover, offering a holistic view of the evolving landscape.

“The upper limit of the evergreen broad-leaved species was also correlated with winter temperature, which means as the temperature increases, the upper limit of the evergreen broad-leaved species shifts upwards. Timberline is one of the most conspicuous boundaries between forest and alpine that attracts researchers’ interest,” said Changa Tshering.

Regions above 3,500 masl are particularly vulnerable to the impacts of climate change, with 31 percent of Bhutan’s total area falling into this category.

This region is home to 83 percent of the country’s protected areas and 1.3 percent of the population, who rely on yak herding practices. The amplified warming in these areas is affecting alpine pastures, leading to decreased productivity of yaks, cattle, and other animals.

The study also highlights a concerning reduction of 22 percent in meadow areas, endangering critical flora and fauna such as the red panda, musk deer, and snow leopard.

Bhutan, committed to maintaining 60 percent of its total area under forest cover and achieving carbon neutrality, faces a dual challenge of developmental activities and climate change impacts eroding its forest cover.

While the study sheds light on these concerning developments, certain aspects, such as the socio-economic impact sector, have not been extensively examined due to time constraints.

Furthermore, the extent, direction, and scale of the treeline shift still require further investigation. The study relied on satellite data without field validation and lacked a detailed correlation analysis between temperature change and treeline patterns.

Nevertheless, Bhutan’s treelines are on the move, signaling a pressing need for concerted efforts to combat climate change and protect its fragile highland ecosystems.

As global temperatures continue to rise, the profound impact on the natural world becomes ever more apparent—since the 1960s, the global mean surface temperature has increased by 0.6 Celsius.