Lush green forests, shrouded in mist. High rainforest canopies so dense that the light of the midday sun hits the ground only in bleak, pencil-thin streaks. Dark, wet forest floors, where bright-coloured fungi unfurl. These are common images of the Western Ghats, a world-renowned biodiversity hotspot that runs roughly parallel to India’s west coast. But this mountain range also comprises several unique, non-forest habitats. These range from seemingly barren rocky plateaus that burst into life for just a few months every year, to rare grassland swamps, home to herbs and grasses found nowhere else on earth.
One of these habitats is the montane grassland, distributed on the high slopes of mountain ranges right from the Ashambu Hills in the southernmost sections of the Ghats in Tamil Nadu, to the Baba Budan range in Karnataka. These grasslands occur on hillslopes alongside sholas (patches of stunted evergreen forests, that grow in valleys) usually at elevations higher than 1,200 metres above sea level.
High levels of plant endemism (species that grow in no other region) are common here. Some examples of these are the red-berried Cotoneaster buxifolius and Lilium neilgherrense.
These open habitats also support several endemic and threatened animal species including the charismatic Nilgiri tahr. Various factors such as fire and temperature are thought to maintain this forest-grassland mosaic. According to a study published in July 2019 by a team including ecologist Atul Joshi of Bengaluru’s National Centre for Biological Sciences, frost and freezing temperatures prevent shola trees from establishing themselves in the adjoining high-elevation grassland patches of the Nilgiris in Tamil Nadu.
Within some shallow valleys of these high-elevation grasslands occurs yet another unique habitat: wetlands or grassland swamps. In the Nilgiris (where they have been most documented), these wetlands are very rare and only occur in some of the southwestern parts of the plateau, says Godwin Vasanth Bosco, who studies and restores shola-grassland systems in the hill range.
In 2012, researchers found 78 plant species in just 5 swamps (the biggest of which was only 4 hectares large) in the Kundah and Upper Bhavani Reserve Forest areas of the Nilgiris. Of these, 28 species are endemic to the Western Ghats, showing how unique the flora of these swamps are . The threatened tussock grass Eriochrysis rangacharii, which was considered extinct for nearly 100 years and was rediscovered by science in 2003(though the indigenous Toda communities of the Nilgiris knew of its existence) is also one of the plants endemic to these wetlands.
Not just rock and stone
North of the Nilgiris, especially in Karnataka and Maharashtra, cliffs and rocky plateaus — collectively called rocky outcrops — host very different plant and animal communities. These protruding masses of bedrock above the soil surface are very distinct in terms of both flora and fauna when compared to the surrounding evergreen forests, says doctoral researcher Ashish Nerlekar of Texas A&M University, USA. He has explored outcrops such as these in Kaas, Chalkewadi, Koyna, Dajipur, Amboli, Bhimashankar and Lonavala, and studied plant species in some of them.
In 2012, a study of laterite rock plateaus, at elevations below 100 metres, in coastal Uttara Kannada, Karnataka, revealed 140 flowering plant species, dominated by seasonal herbs that flower during the peak of the monsoons. Another study the same year recorded 356 plant species from 10 sites containing rocky outcrops in southwestern Maharashtra. From a study in 2013, ecologist Aparna Watve reported 132 plant species from 6 rocky outcrop sites in Maharashtra; among these, 57 species were endemic.
“As per various reports, the lateritic plateaus of the northern Western Ghats hold more than 50 per cent of total endemic species,” says scientist R K Choudhary of Pune’s Agharkar Research Institute whose team documents plant diversity in these outcrops.
Over the years, scientists have been discovering several new species in these outcrops. Examples are Chlorophytum gothanense (of the spider plant family) and several species of pipeworts such as Eriocaulon parvicephalum recorded by Choudhary and his colleagues in 2017. In 2014, researchers also discovered a new species of gecko — Giri’s day gecko (Cnemaspis girii) — in the Kaas region.
Long list of threats
As diverse as these habitats are, so are the threats they now face. Scientists at the Indian Institute of Science who studied laterite outcrops in Karnataka noted how acacia and cashew trees were being planted in these habitats because they were considered “infertile and barren”. Bauxite mining too is a concern in some lateritic plateaus in western Maharashtra.
“Many of these habitats in the northern Western Ghats are seriously threatened by developmental activities. Many endemic species here are habitat specialists and these disturbances could result in their extinction,” says Choudhary.
According to Nerlekar, the lack of ecological data to effect conservation policies is the greatest conservation challenge that this habitat faces. “Many studies cite grazing and fire as ‘threats’ without even a pinch of scientific experimental data to back such towering claims,” he says. “Ecology coupled with sound social science research should drive conservation policies, and that is what is missing for these rock outcrops. It is high time we move on from a natural history-taxonomy based understanding to evidence and experiment-based science for these habitats.”
Down south in the high reaches of the Ghats, the montane grasslands are struggling too. A study by a team including scientist V V Robin of the Indian Institute of Science Education and Research, Tirupati, published earlier this year finds that over the last four decades alone, we’ve lost almost one-fourth of these grasslands. Primarily they’ve been lost to introduced alien invasive trees such as pine and acacias, that continue to invade these open habitats long after the planting of exotic trees in the landscape has ceased.
Invasives are also eating into the Nilgiri grasslands, says Bosco. “Excessive carbon dioxide in the atmosphere and increased temperatures, are big disadvantages for these grasses…fast growing invasive species are favoured in this climate,” he suggests.
According to Joshi and his co-authors in the new study (which confirms that frost maintains the montane grasslands of the Nilgiris), the introduction of the exotic and invasive black wattle tree “has changed the balance between frost and tree recruitment in this ecosystem”. Black wattle is native to some temperate regions in Australia and New Zealand. The scientists’ temperature experiments reveal that black wattle seedlings are more tolerant to frost (unlike the native shola trees) and showed higher germination in the threatened grasslands. Their experiments also demonstrate that warmer night temperatures helped seedlings of both native shola trees and invasive black wattle survive in open grasslands, suggesting that increased temperatures due to global warming could cause trees to take over these montane grasslands.
Another threat to native grasslands of the Nilgiris and the Palni-Anaimalais is neglect and mismanagement, says Bosco. “People all over the globe still want to plant trees if they want to plant something,” he says. “Grassland species identification and knowledge of this native ecology is still lacking.” According to Bosco’s estimates, over 90 per cent of the original wetland habitats in the Nilgiris might have already been lost, submerged under reservoirs and converted into agricultural land and settlements. A study in 2014 noted that local government agencies consider these swamps as wastelands and that there is “a lack of awareness of both the floristic diversity of swamps and their ecological value”.
The endemic Eriochrysis rangacharii grass that thrives in the swamps is no longer flowering or setting seed, probably due to climatic stress, according to Bosco. “Excess carbon dioxide in the atmosphere puts grasses at a photosynthetic disadvantage. Their growth cycles might be affected due to this,” suggests this author of Voice of a Sentient Highland, a book on the ecology of the Nilgiris and “intelligence in nature” which hit the shelves in May 2019.