Being higher and out of reach is probably saving Sikkim’s high-altitude tropical forests. Scientists find that land-use patterns changed more drastically in the more-accessible lower regions, causing a staggering 16% decline in primary broadleaved forest cover in the Sikkim Himalaya.
Primary forests, which host native vegetation and are still undisturbed by human activities, are declining worldwide. Globally, more than 40 million hectares of such forest have been converted for other uses since 2000. A majority of this has been in the tropics, where logging and clearing forests for industrial development are concerns. Human activities also transform primary forests into agricultural land and secondary forests (disturbed forests which replace logged primary forests).
Unfortunately, this is common in the broadleaf forest tracts of India’s Sikkim Himalaya which thrive between 1,000-2,800 metres above mean sea level. When researcher Radhika Kanade of Bengaluru’s Ashoka Trust for Research in Ecology and Environment (ATREE) went looking for primary forest patches in the lower reaches (around 1,000 m) here, she could barely find any. However, most of the slightly higher reaches (2,000-2,800 metres, which were difficult to access due to the terrain), still supported primary forests.
Wondering if topography, such as the presence of steep terrain, could be influencing this pattern, Kanade and Robert John (Indian Institute of Science Education and Research, Kolkata) studied satellite images from 1990 to 2013 to examine the land-use changes near Sikkim's Teesta river.
They surveyed several areas between 2011 and 2013 to confirm current land use.
The team's results, published in the journal Applied Geography, show a 16% decline in primary forest cover in this Eastern Himalaya biodiversity hotspot. This is higher than regional level declines reported so far (such as the 8.4% decline in Southeast Asian forest cover estimated by the Global Forest Resources Assessment in 2015). A staggering 14,740 hectares of primary forest was transformed during the 23-year period — some into secondary forest, parts of which again transitioned to agricultural land.
The scientists’ hunch was right: elevation, slope and aspect (the direction a slope faces) influenced land-use patterns. Agricultural areas steadily expanded, mainly in the lower regions. Undisturbed primary broadleaved forest is now restricted to higher reaches that are relatively difficult to access and unsuitable for activities like agriculture and agroforestry.
“These higher-altitude areas are also legally protected and this plays a role too,” says Kanade.
