Tropical montane grasslands (TMG) in the Shola Sky Islands of the Western Ghats have suffered big reductions due to invasions by exotic trees such as acacias, pines and eucalyptus, shrinking the range sizes of endemic species, including plants, birds, amphibians and mammals. Some populations are being driven to local extinction.
But researchers have now identified areas suitable for grassland restoration and conservation to reverse the decline.
Reporting on their study titled ‘Opportunities and challenges in using remote sensing for invasive tree species management, and in the identification of restoration sites in tropical montane grasslands’ earlier this month in Science Direct, M. Arasumani, V.V. Robin and Milind Bunyan from the Indian Institute of Science Education and Research (IISER), Tirupati, and Ashoka Trust for Research in Ecology and the Environment (ATREE), Bengaluru lay out the possibilities.
They focus on identifying grassland restoration sites using satellite images with a high spatial resolution (RapidEye), and have recommended careful removal of young and isolated exotic trees at the invasion front and restoring grasslands, instead of removing dense stands of mature exotic trees.
TMG are high elevation grasslands forming only 2% of all grasslands in the world. Among their functions is regulating the global carbon cycle and serving as a source of water to downstream communities. Researchers say grasslands do not benefit from conservation and restoration efforts afforded to tropical montane forests, possibly due to limited information. “In India, TMG have even been classified as wastelands in forest management plans since they are unlikely to generate revenue, contrary to the timber (even if exotic) found in forests,” the study says.
Loss of grasslands due to invasive exotic trees is a “novel threat” through the establishment and expansion of exotic tree plantations. In the Western Ghats, 23% of montane grasslands were reportedly converted into invasive exotic tree cover over a period of 44 years.
Attempts to manage invasive exotic trees in montane grasslands incorporated approaches that include prevention and mechanical, chemical and biological control. “For invasive species such as Acacia mearnsii that grow rapidly and disperse seeds widely, removing mature trees is often ineffective. An approach that targets the removal of young exotic trees would be more effective. Similarly, restoring grasslands where isolated but mature trees exist in grassland patches could be an easy way to restrict further dispersal,” the researchers say.
“Our study identified an area of 254 sq km for grassland restoration, 362 sq km of intact montane grasslands for conservation, and 606 sq km of mature exotic tree stands in the Nilgiris, Palani Hills and Anamalai. Most of the areas suitable for montane grassland restoration were located in the Nilgiris (126 sq km), followed by the Palani Hills (73 sq km), and the Anamalai (55 sq km). The largest areas for grassland restoration were in reserve forests (87 sq km), followed by wildlife sanctuaries (60 sq km) and national parks,” the study says.
The Palani Hills and Anamalai lost grasslands due to invasive species, Mr. Bunyan told The Hindu . Most of these species were planted, but that programme was stopped around the 1990s, and since then, they were purely invasive, he explained. The species have a very high seed bank, about which nothing can be done, but cutting them will require multiple cycles, he added.
The study also throws light on policies for grasslands, which are seen as having no productive use, as is often alleged in the case of the Hesaraghatta grasslands in Bengaluru. “Grasslands are not wastelands. Though they are not being put to use, we are benefiting in other ways - such as serving as pasture. In the Sholas, they are responsible for hydrological recharge,” he said.
