Remote-sensing data help track shift of alpine treeline in Himalayas

Written by Ajay Sukumaran | Updated: Feb 27 2012, 08:56am hrs
The treeline in the alpine zone of the Himalayas has been known to fluctuate, often shifting to higher elevations closer to the snowline because of warming caused by greenhouse gases. In a study thats among the first to map this phenomena over a large area of the mountain range, researchers have quantified the extent of the shift based on data from the Indian Space Research Organisation's remote-sensing satellites.

A paper by scientists at the agencys Space Applications Centre (SAC) in Ahmedabad and the Dehradun-based Forest Research Institute, published earlier this month in Current Science, puts the mean upward shift of the alpine treeline at around 388 metre, plus or minus 80 metre.

The alpine life zones are the areas lying between the treeline and the snowline and its ecosystem is known to be highly endemic and sensitive to temperature change, making it an ideal setting to study climate impact. Typically, the alpine treeline is the uppermost elevation where individual trees as tall as two metre can be found, and it is a transition zone from dominant trees to shrubs or grassland.

The SAC paper covered the whole of Uttarakhand, the first time an entire state has been mapped, though there have been similar studies at specific sites, notes CP Singh, a scientist at SAC and the lead author of the paper. Most of the research on alpine treeline shift has primarily been based on field data with a limited geographical extent, the paper notes. The study is part of an umbrella project being conducted under Isros Earth Observation Application Mission using remote-sensing data.

The upward shift of vegetation observed in Uttarkhand also raises the concern of shrinking grasslands, known locally as bugyal, says P Soni, former head of the Forest Ecology and Environment Division at the Forest Research Institute, Dehradun, who participated in the study. The grasslands act as a sort of buffer between the snowline and treeline and is a permanent vegetation cover that typically holds the soil and helps to retain moisture.

They are a very important part of the food chain for herbivores at the higher altitude, says Soni. This was a first-of-its-kind study where we have reported how vegetation has been ingressing the bugyals and the fact is that if this pace keeps on increasing, the bugyals will be finished. While 19% of Uttarkhands area comprises permanent snow cover, glacier and steep slopes devoid of vegetation, about 65% of its area is covered by forests. Nearly 29% of the state is at an elevation of 3,000 metre, which is generally considered a zone of sub-alpine and alpine trees.

The research showed that the average elevation of the current treeline in the state was 3,542 metre, while the treeline during the 1970s was 3,166 metre. Thus, there is a mean upward shift of the treeline of the order of 388 plus or minus 80 metre, the study reported.

The current treeline stretched across a surface distance of 2,962 km compared to 1,650 km in the 1970s, which the researchers attributed to the zigzag nature of the ingression along the gradients. Moreover, the current treeline encounters more surface distances from one hill to another due to its higher positioning, the researchers note.

In other sites like the Valley of Flowers, there have been other kinds of disturbances, including movement of people. In this area, we can safely say that this is only because of climate change, says Soni, adding that the study also recorded the details of the species ingressed in these areas. Apart from satellite images, the team also used ground stations to study the vegetation.

The SAC paper says that a programmatic initiative in line with the Global Observation Research Initiative in Alpine Environments (Gloria) is the need of the hour to track these trends over the long term. An international data reporting project that began in 2001, Glorias objective is to maintain a worldwide observation network in alpine environments to help study trends in species diversity and temperature.

In a recent paper on the projected impact of climate change on forest ecosystems in India based on climate modelling, researchers from the Indian Institute of Science (IISc) noted that the upper Himalayan stretches and other mountainous forest grids were particularly vulnerable to the adverse impact of climate change, primarily because the change is predicted to be larger for regions with greater elevations. Their assessment indicated that, at the national level, about 45% of the forested grids were likely to undergo change by 2035.

Natural migration of species, however, is not easy in India because of fragmented forests, agriculture and the presence of villages and roads, says NH Ravindranath, professor at the IIScs Centre for Sustainable Technologies, who was one of the authors of the climate impact assessment. Observational data on phenology of forests in India has been inadequate while there is a lack of intensive monitoring along the altitude gradient, he adds.

The IISc study has recommended the initiation of long-term monitoring of vegetation response to changing climate and suggests that climate change be incorporated in all forest conservation and development programmes.