- The unique high elevation grasslands of the Western Ghats have long been viewed as wastelands and planted with exotic tree species like Eucalyptus, pine and wattle.
- Although plantations have now stopped for over three decades, scientists report that existing trees have spread, replacing much of the grassland ecosystems in the Nilgiri, Palani and Anamalai hills.
- Several endemic species of birds like the Nilgiri pipit, which are only found in grasslands in the worst affected ranges, are likely to be severely threatened.
In many ways, the Western Ghats is a study in contrast. While the foothills and slopes of the mountain range are covered in dense rainforest, the higher reaches are a completely different ecosystem. Across Kerala, Tamil Nadu and Karnataka, the three states that have the highest mountains of the Western Ghats (1,200 metres to 2,600 metres), forests open up into vast grasslands dotted with small clumps of stunted evergreen trees called shola forests.
The differences don’t end there. While the lower reaches of the Western Ghats suffer from deforestation, a new study says that the grasslands of the mountain tops are under threat from an influx of exotic trees.
Grassland ecosystems across India have been considered wastelands since the British Raj – a perception that still exists. In the montane (high elevation) grasslands of the Western Ghats, this perception coupled with a need for timber and pulpwood had led to large scale plantations of exotic trees like eucalyptus, wattle and pine by the British and, after independence, by the Indian Forest Department.
Planting stopped in the 1980s, when the timber demand declined, and local environmentalists began to campaign against drought-inducing trees like eucalyptus in some habitats. But the old trees remained, including in popular hill stations like Ooty in the Nilgiris and Kodaikanal in Palani hills in Tamil Nadu, and Munnar in the Anamalai hills in Kerala.
Three decades on, what has the existence of these plantations done to the landscape? Are these benign relics of a misguided management or have they affected the unique shola-grassland ecosystems of these mountains?
Six ecologists – V.V. Robin , M. Arasumani and Danish Khan from the Indian Institute of Science, Education and Research (IISER Tirupathi), Milind Bunyan from the Ashoka Trust for Ecology and Environment (ATREE), C.K. Vishnudas from the Hume Institute of Ornithology and M. Muthukumar from Gandhigram Institute of Rural Ecology – came together to answer these questions.
Robin, who is an assistant professor at IISER Tirupathi, explained that several biologists and environmentalists working in different parts of the Western Ghats had felt that the high grasslands were in decline and exotic trees were thriving. His co-author, C.K. Vishnudas was one of them.
Vishnudas, an ornithologist, has worked in the Western Ghats for nearly 20 years, conducting bird surveys and visiting areas like the Mukurthi National Park and the Eravikulam National Park almost every year. “In some of these mountain tops, I started noticing exotic species, for example wattle and eupatorium and eucalyptus,” he said. “I could see that they were slightly moving into the plateau (at the top of the Eravikulam National Park) and spreading into the mountains.”
Meanwhile in a separate study (in which Vishnudas was not involved), Robin and his colleagues found that in the Palani hills over 60 percent of the original grassland and 30 percent of the shola forest had been lost. Invading exotic plantations had played a big role in this, although other activities like agriculture also had an impact.
The researchers decided to expand the study to a larger area covering all of the shola-grassland habitats in Karnataka, Kerala and Tamil Nadu. The study compared satellite data from 1973, 1995 and 2017 to see how different elements of the landscape, including shola grasslands, plantations and agriculture fields had changed. They also confirmed the most recent changes in the landscape composition by conducting field surveys.
Intact forests and vanishing grasslands
Between 1973 and 2017, about 66 percent of the total grasslands lost had been because of exotic trees spreading. Agriculture accounted for another 21 percent of the grassland loss while tea plantations, cane invasion and human settlement accounted for the rest. Grasslands in the northern part of the study area, such as the Brahmagiri and Kudremukh ranges, and in the southern Western Ghats in areas, like Srivilliputtur, were almost unchanged in this time period. These regions were probably saved by the lack of exotic timber plantations and due to isolation.
Most of the grassland loss was concentrated in the Nilgiri, Palani and Anamalai mountains, which is where most exotic plantations as well as the most extensive shola-grasslands are concentrated in the Western Ghats. The accompanying shola forests, however, were largely well-preserved according to the study, a result that is contrary to popular perception.
Atul Joshi, an ecologist and a doctoral student at the National Centre for Biological Sciences, praised the study for providing information on the changes in the grasslands, shola forests and exotic trees. Joshi, who is not involved in the study, studies the impact of past and current human activities as well as the role of soil and climate change on the shola-grassland ecosystems. He particularly flagged the finding that grasslands incurred far more damage than shola forests.
This finding seems to stand out because it challenges popular perception and the attention that is paid to shola forests by conservationists and forest managers. “Yes, this was a big surprise for us,” said Robin. “Most of us have spent our careers studying and believing in forest conservation, but the data and the facts are that our protection system are doing very well in the last few decades to preserve the existing forests.”
Other ecologists are, however, unsurprised by this finding. “This is consistent with the findings of our study that the assumption – grasslands are wastelands – led to large-scale depletion of grasslands, thanks to a century of alien tree plantations,” said Joshi. “Shola forests, on the other hand, got some protection for conservation of water sources and also for aesthetic reasons.”
Madhusudan Srinivasan, a plant ecologist from the University of Kentucky and not connected to this study, pointed out that grasslands were also more susceptible to being taken over by exotic species than forests. “The inherent closed nature of the sholas makes them a little more resilient to invasion by wattle and broom, which tend to need light to grow,” he said.
Robin cautioned, however, against seeing this as sign that sholas were thriving. The study could not shed light on the quality of the existing shola forests; it only showed that they had remained relatively stable since the 1970s, he explained.
“We are also unable to asses change before 1970s, as they were no satellite images then,” he pointed out, adding: “We do know that even in the earliest imageries, over 50% of the landscape had already been modified. This change presumably included loss of forests. What this means is that whatever forests we lost was during the colonial times, but the forests are stable today. The biggest threat is to the grasslands.”
Impact and solutions
What could the shrinking grassland mean for this landscape?
Although comprising only three percent of the Western Ghats, the shola forest-grassland habitat is home to about 48 percent of all endemic amphibians and birds found in the Western Ghats. One such bird is the Nilgiri pipit Anthus nilghiriensis, named after the mountains where its habitat is rapidly disappearing. In a 2014 study, Robin and Vishnudas reported that the bird is only found in grasslands in mountains that go above 1900 metres. Although the study found intact grasslands in lower altitude mountain ranges such as Brahmagiri in the north and Ashambu hills in the south, they did not find any sign of the Nilgiri pipit there. So, the higher and cooler grasslands, found only in the Nilgiris, Palanis and Anamalais appeared to be its only refuge.
But Robin and Vishnudas assert that the Nilgiri pipit was already threatened here from the spread of exotics. “Vishnu and I had documented local extinction of the species from parts of the landscape,” said Robin referring to the 2014 study. “Unfortunately, the situation appears to be even more severe than we anticipated.”
Srinivasan added to this grim assessment by pointing out the added effect of global warming. “These high altitude species have no place higher to move because of warming,” he said. Apart from this, the grasslands of the Western Ghats are vital to herbivores such as the Gaur Bos gaurus and the Nilgiri Tahr. In the Nilgiris, the grasslands have also historically supported cattle and buffalo herding by indigenous communities like the Badagas and Todas respectively. The solution to this issue appear to be multifold.
“I think, our foremost priority should be to protect whatever is left,” said Joshi. A sentiment that Srinivasan and Vishnudas also shared.
What would such protection mean? “Although the traditional view that protected areas (PAs) protect habitat is partly true (most extant grasslands are in PAs today), invasion is rapidly encroaching into this landscape,” said Robin. The study looked at PAs in the study area to see if grasslands there were less impacted by invasive species. The Eravikulam National Park was created in 1978 and excluded from most of the plantation drives.
Additionally, the forest department used controlled fires to encourage grass growth for its prize flagship species, the Nilgiri Tahr. This combination, the study found, resulted in Eravikulam being the least invaded grasslands of the three. However, the Kodaikanal Wildlife Sanctuary was only established in 2013, by which time the grasslands were already overrun by exotics.
In grasslands that have been invaded, there is a call to remove exotic trees. For instance, the Madras High Court in 2014 expressed concern for the sholas and grasslands of the Western Ghats and ordered the removal of eucalyptus and pine in Kodaikanal. “I don’t know whether clear felling of these trees would be helpful for grassland restoration in the long run. It may provide an opportunity for the grasses to comeback but may also pave the way for other invasives and may require constant checks to prevent re-invasions – not an easy task,” warned Joshi.
Ironically, Robin noted that even though forest department officers were of the view that exotics should be removed, there were legal hurdles like the law against cutting trees in protected areas, which made it hard to remove exotic trees from inside Kodaikanal Wildlife Sanctuary.
Arasumani, M., Khan, D., Vishnudas, C. K., Muthukumar, M., Bunyan, M., & Robin, V. V. (2019). Invasion compounds an ecosystem-wide loss to afforestation in the tropical grasslands of the Shola Sky Islands. Biological Conservation, 230, 141-150.
Joshi, A. A., Sankaran, M., & Ratnam, J. (2018). ‘Foresting’the grassland: Historical management legacies in forest-grassland mosaics in southern India, and lessons for the conservation of tropical grassy biomes. Biological conservation, 224, 144-152.
Srinivasan, M. P., Bhatia, S., & Shenoy, K. (2015). Vegetation-environment relationships in a South Asian tropical montane grassland ecosystem: restoration implications. Tropical Ecology, 56(2), 201-217.
Robin, V. V., Vishnudas, C. K., & Ramakrishnan, U. (2014). Reassessment of the distribution and threat status of the Western Ghats endemic bird, Nilgiri Pipit Anthus nilghiriensis. Current Science, 622-630.
Banner image: The changed landscape of the upper plateau in the Nilgiris. While the plantations have eaten into the grasslands, the original shola forests is a small patch in the foreground right. Photo by S. Gopikrishna Warrier / Mongabay.