Western Ghats are among the earth’s oldest tropical hills. The 1,600km-long hill range is 50-100 million years older than the Himalayas. Renowned geologist B. P. Radhakrishna writes in a 1993 study, that a domal uplift and faulting created the hill range.

There are topographic differences between the western and eastern aspects of the Western Ghats which are the reasons for the unequal west-east distribution of rainfall. A fifteen-fold difference in annual rainfall between the driest and wettest spots in the Western Ghats, has been documented.

The average annual rainfall is 2,500 mm in the narrow eco-region. However, what makes the Western Ghats states different from each other is the length of their dry season. In the regions closer to the equator, the dry season is shorter and farther north, it can be six or even nine months long, as that in northern Karnataka and Maharashtra. Western Ghats can thus be divided into two unequal segments; equatorial southern Western Ghats with two to five dry months and the monsoon-driven northern Western Ghats with six to nine dry months. The narrow zone of transition lies between Mangalore and Udupi in southwestern Karnataka.

Rainfall patterns mainly drive the region’s biodiversity, endemism, and ecological fragility, with altitude playing a secondary role. While biodiversity and endemism can be easily assessed, measuring ecological fragility depends on factors such as soil, rocks, altitude, and slope, which change slowly, and biotic succession, which can occur rapidly due to human activities.

Vegetation, succession and ecological fragility

Biotic succession is most evident in the structure and composition of the local vegetation. Research by a French plant-geographer J. P. Pascal has shown that parts of the Western Ghats support wet evergreen forests. Secondary successions of this vegetation type have varying proportions of deciduous trees.

Ecological fragility, within wet zones, can be measured using the proportion of deciduous trees in the secondary forests. The most general pattern in the Western Ghats is that secondary forests with a longer history of human disturbance have proportionately more deciduous trees, and the proportion of deciduous trees increases with the length of the dry season. Selective logging and clear-felling of wet evergreen forests have led to the succession of deciduous trees, bringing with them a series of recurring ecological problems such as fire, grazing and invasion of alien species of plants. Resultant changes in the character of the topsoil lead to gully-erosion and landslides. The problem is exacerbated by longer dry season. Wet zones of the northern Western Ghats are therefore more vulnerable to landslides.

Deforestation triggers landslides

The recent landslides in Wayanad have transpired a lot of debate about the apathy of governments and the lack of adherence to scientific protocols in managing the ecologically sensitive Western Ghats. During the southwest monsoon of 2024, Uttara Kannada district witnessed one of its most devastating landslides. During the eighties, I spent five years in Sirsi, and travelled throughout the more than 10,000km² in the northern district.  At that time, Uttara Kannada was ranked number one among the districts of the Western Ghats in terms of forest cover. Close to 80% of the district was covered with forest, majority of which was classified as wet evergreen. Farmers in the district, traditionally practiced a system of multi-tiered horticulture including betelnut, cardamom, black pepper, banana, cocoa and nutmeg fertilised almost entirely using organic manure. Multi-tiered horticulture was confined to the valleys and was augmented by homestead dairy. The integrated traditional farming system that was seen to be both biodiversity-friendly and sustainable, attracted researchers from far and wide. Currently, the district is left with only 48% forest cover. However, the average rainfall of 2,500 mm has not changed; nor has the prolonged dry season that characterises the northern Western Ghats.

The southernmost Western Ghats district Kanniyakumari, where I hail from, witnessed devastating landslides in 1992. Many lives were lost. The heavy rains that caused landslides also changed the course of a perennial stream. I have crossed this stream many times walking across an old British era iron bridge. The sturdy bridge was also damaged and rendered unfit for further use. The Western Ghats of the small district have been heavily impacted by deforestation for the sake of timber, raising rubber, tea, coffee, clove, cardamom and a variety of other horticultural crops, by the public and private sectors. Bamboo-like reeds (Ochlandra) that lined the streams were practically wiped out to supply raw material to distant paper mills.

Read more: [Commentary] Why the Wayanad landslide must not fade from memory

Archean rocks and massifs

The equatorial southern Western Ghats enjoy the added benefit of inheriting the oldest underlying rocks of India. These two billion years-old rocks have contributed immensely to the segment’s geological stability. It is for this reason that the India-based Neutrino Observatory was proposed to be located in the segment. With stable underlying rocks and equatorial climate, the southern Western Ghats are better-insulated against tremors and landslides.

The segment is also very rich in biodiversity including hundreds of endemic species – a unique feature that gained worldwide recognition and resulted in the establishment of India’s first biosphere reserve the Nilgiri Biosphere Reserve in 1986. Many years later, the Agasthyamalai Biosphere Reserve was added to conserve the southernmost parts of the segment. The intervening distance between the two is less than 500km.

The southern Western Ghats are also where massifs that are 2,000 m or more above sea level are located. Anaimudi and Dodabetta that cross the 2,600 m mark are the highest peaks. The elevated matrix within which the two peaks are located, are characterised by Pleistocene relics and frost-adapted montane vegetation. The shola-grassland complex is crucial for the survival of the Nilgiri tahr, the only tropical mountain goat, and the Nilgiri pipit, a rare, endemic bird. The Palghat gap, has split the matrix separating the Nilgiris from the Anamalai and Palani hills.

God’s own country

Kerala enjoys equatorial climate as it is relatively closer to the Equator than to the Tropic of Cancer. It is the equatorial climate that has made it ‘God’s Own Country’. Equatorial regions are the richest in biodiversity, resilient, and capable of ‘bouncing back’ after disturbances including those inflicted by humans and their machinery. However, sustained impacts can alter natural ecosystems and push them into irreversible states.

What is remarkable about Kerala is that it continues to support some of the most biodiverse landscapes and waterscapes in the country. If endemism in species is used as a yardstick for assessing the natural wealth of any Indian state, Kerala would no doubt top the list. A project in 2012 supported by the Critical Ecosystems Partnership Fund, jointly executed by Care Earth Trust and the French Institute of Pondicherry, added spatial information for 454 species of endemic vertebrates to the Western Ghats Biodiversity Portal.  Analysis of the data revealed the occurrence of 62% of the species in Kerala, and 22% exclusive to the state.

It is important to realise that Kerala is the state with the highest human population density in the Western Ghats. Both biosphere reserves in the southern segment have included parts of the state. Further, Kerala has contributed enormously to our understanding of the biodiversity of the southern Western Ghats.

It is also noteworthy that Carlos Linnaeus’ system of assigning standard binomial scientific names to plants and animals may have been influenced by practitioners of traditional medicine in the erstwhile Malabar. India’s legendary birdman Salim Ali’s direct involvement with the birds of the Western Ghats started from the south with the launch of his surveys in the princely states of Travancore and Cochin. Years before geo-tourism, biodiversity-tourism or bird-tourism became a popular enterprise in India, they were operational in Kerala. More importantly, the earliest and most successful case of environmental activism in India is what began in the state fifty years ago resulting in the highly contended Silent Valley being declared a national park.

Greater vigilance and commitment are paramount in preventing future calamities in the Western Ghats. Holistic management of the Western Ghats and its natural resources, guided by science and people’s aspirations, is the need of the hour. This should begin by addressing the critical socio-economic and ecological concerns of Kerala. After all, Kerala has provided a great service to the country in cradling a significant part of its endemic biodiversity. It is the flagship of the Western Ghats and a hotspot within a globally recognised biodiversity hotspot.

CITATION:

Radhakrishna, B.P. (1993) Neogene uplift and geomorphic rejuvenation of the Indian peninsula. Current Science 64(11&12): 787-793. https://www.jstor.org/stable/24096189

Daniels, R.J.R. and Vencatesan, J. (2008) Western Ghats: Biodiversity, People, Conservation. Rupa & Co, New Delhi.

Daniels, R.J.R. (1992) Geographical distribution patterns of amphibians in the Western Ghats, India. Journal of Biogeography 19:521-529. https://www.jstor.org/stable/2845771

Pascal, J.P. (1988) Wet evergreen forests of the Western Ghats. French Institute, Pondicherry. https://www.researchgate.net/publication/242385641_Wet_Evergreen_Forest_Types_of_Southern_Western_Ghats_India

Ranganathan, J., Daniels, R.J.R., Subash Chandran, M.D., Ehrlich, P.R. and Daily, G.C. (2008) Sustaining biodiversity in ancient tropical countryside. Proceedings of the National Academy of Sciences (USA) 105 (10): 1073-1074. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2577706/

Daniels, R.J.R. and Daniels, A.E.D. (1993) Deforestation catalyzes flood devastation. Down to Earth 15:46-47.

The author is an ecologist with the Care Earth Trust, a Chennai-based biodiversity and conservation organisation.

Banner image: Monsoon view of the Sengottai Gap or Aryankavu pass in the Western Ghats as seen from Sengottai, Tamil Nadu towards Aryankavu, Kerala. Image via Wikimedia Commons (CC0 1.0).

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BiodiversityConservationEndemic speciesProtected AreasIndiaKeralaWestern Ghats

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