The South Western Ghats Montane Rain Forests
The Western Ghats are a chain of mountains and hills running along the western seaboard of India. They separate a narrow band of lush green coastal plains (Konkan to the north, Malabar to the south) from a hot and dry plateau (the Deccan) in the interior. The Western Ghats are a biodiversity hotspot. The Varayadu or Nilgiri Tahr (Nilgiritragus hylocrius) inhabits a complex of forests and grasslands in the southern half of this mountain belt. Geologists claim that they were formed during the disintegration of the southern super-continent of Gondwanaland. Because of the abundant rainfall they receive, the Ghats shelter luxuriant vegetation – moist deciduous forests in the lower reaches, and montane rain forests at higher altitudes.
The northern half of the Western Ghats are drier on account of lower precipitation. They support the North Western Ghats Moist Deciduous Forests and North Western Ghats Montane Rain Forests. The wetter southern half harbours the South Western Ghats Moist Deciduous Forests and South Western Ghats Montane Rain Forests. This post is about the last ecoregion, found at altitudes of 1,000 metres and more above the sea level in the states of Tamil Nadu and Kerala. They are especially rich in flora and fauna with a high degree of endemism. Not only do they have the highest peaks of the entire mountain chain but the wettest areas of South India.
The Southwest (June-July-August-September) and Northeast Monsoon (October-November) rains dump as much as 2,800 mm of precipitation. But the lay of the land is such that some parts are three times as wet. The cool and wet climate, high elevation and complex topography of the chain have created favourable conditions for the evolution of plant and animal species found nowhere else on the planet. These factors explain the tremendous biodiversity of the South Western Ghats Montane Rain Forests. This is how the World Wildlife Fund for Nature (WWF) describes the ecoregion:
The South Western Ghats Montane Rain Forests are the most species-rich ecoregion in the Deccan Peninsula. They also harbor the highest levels of endemics. Consider the numbers: 35 percent of the plants, 42 percent of the fishes, 48 percent of the reptiles, and 75 percent of the amphibians that live in these rain forests are endemic species. Ten mammals and thirteen birds are endemic or near endemic to the ecoregion. More than 80 percent of the flowering plants characteristic of this mountain range are in the species-rich forests of the south.
Large, charismatic mammals such as the tiger (Panthera tigris), Asian elephant (Elephas maximus), sloth bear (Melursus ursinus), gaur (Bos gaurus), and raucous hornbill inhabit the forests. These species evoke images of wild jungles of the Indian subcontinent. Large expanses of high-elevation, undulating grasslands interspersed with patches of stunted shola forests harbor the endemic Nilgiri tahr and India’s largest elephant population. Every twelve years, the blue flowers of Neelakurunji (Phlebophyllum kunthianum) impart a blue hue to these grassland-shola mountains.
This ecoregion represents the montane rain forests above 1,000 m along the southern half of the Western Ghats. It extends as a long and narrow unit through the Indian states of Kerala and Tamil Nadu. The northern boundary of this ecoregion is the Wyanad, where the habitat makes a transition from the drier forest in the north to the more moist forest in the south. From here the ecoregion runs parallel to the Western Ghats Mountain Range, about 35 km inland, all the way to the southern end of the range. The Deccan Plateau itself was once part of Gondwanaland, evident in relicts of the ancient southern flora and fauna. After becoming detached from this southern continent during the Cretaceous, it drifted northward to finally crash into the northern Laurasian continent. After this initial collision, a series of geological uplifts created the Western Ghats Mountain Range, with several peaks higher than 2,000 m. The highest of these is Anaimudi, which rises to 2,695 m.
As the moisture-laden southwest monsoon winds sweep in from the Malabar Coast and rise above the mountain range, they release more than 2,500 mm of rainfall. The northeast monsoon from October to November supplements the June to September southwest monsoon rainfall, for an average annual precipitation that exceeds 2,800 mm. But because of the deeply dissected topography, some areas can receive more than 8,000 mm of rainfall throughout the year. This produces local variations in habitat types and localized centers of endemism. The Periyar River, which originates from Periyar Tiger Reserve, is one of the larger rivers that carry the monsoon rains east across the peninsula.
The habitat types include the wet montane evergreen forests and shola-grassland complexes in the higher elevations. The montane evergreen forests are diverse, multistoried, and rich in epiphytes, with a low canopy at 15 to 20 m. The forest communities are characterized by Cullenia exarillata, Mesua ferrea, Palaquium ellipticum, Gluta travancorica, and Podocarpus wallichiana. Podocarpus represents a Gondwanaland relict carried across during the long northward journey. Other evergreen species in these montane forests include Calophyllum austroindicum, Garcinia rubro-echinata, Garcinia travancorica, Diospyros barberi, Memecylon subramanii, Memecylon gracile, Goniothalamus rhyncantherus, and Vernonia travancorica.
The montane shola-grassland complexes occur between 1,900 and 2,220 m. These consist of stunted montane forests surrounded by undulating grasslands. The upper story of the forests is characterized by Pygeum gardneri, Schefflera racemosa, Linnociera ramiflora, Syzigium spp., Rhododenron nilgiricum, Mahonia nepalensis, Eleocarpus recurvatus, Ilex denticulata, Michaelia nilagirica, Actinodaphne bourdellonii, and Litsea wightiana. A low, twisted second story of Ilex wightiana, Rapanaea wightiana, Ternstroemia gymnanthera, Symplocos spp., and Microtropis spp. and a dense shrub layer of saplings of Strobilanthes, Psychotria, and Lasianthus spp. usually is present. The grasslands that surround the shola forests consist of several fire- and frost-resistant grasses – Chrysopogon zeylanicus, Cymbopogon flexuosus, Arundinella ciliata, Arundinella mesophylla, Arundinella tuberculata, Themeda tremula, and Sehima nervosum.
The levels of endemism in these montane forests are truly astounding. More than half the tree species are endemic, especially among the Dipterocarpaceae and Ebenaceae. The majority of the fifty endemic plant genera are also monotypic. But the distribution of richness and endemism is not uniform. There are localized areas that harbor exceptional levels of diversity and endemism. For instance, the Agasthyamalai and Nilgiri Hills, recognized as centers of plant diversity, are exceptional for plant richness. A high proportion of the trees in these forests are dioecious breeding systems. In the shola forests in particular, dioecy is quite prevalent among the Lauraceae and Moraceae. Therefore, many of the tree populations are especially vulnerable to deforestation and other disturbances because of mate isolation and reduction of numbers of mates. In the Cullenia-dominated stands, for instance, a large proportion of trees have less than five individuals in a 10-ha area, making them locally rare.
Endemic and Near-Endemic Mammal Species (an asterisk signifies that the species’ range is limited to this ecoregion)
- Soricidae Suncus montanus
- Pteropodidae Latidens salimalii
- Cercopithecidae Trachypithecus johnii
- Viverridae Viverra civettina
- Viverridae Paradoxurus jerdoni
- Bovidae Hemitragus hylocrius*
- Sciuridae Funambulus layardi
- Sciuridae Funambulus sublineatus
- Muridae Mus famulus*
- Muridae Vandeleuria nilagirica*
The Salim Ali fruit bat (Latidens salimalii) and the rodent Platacanthomys lasiurus represent monotypic, endemic genera. The rare and endemic Nilgiri tahr (Hemitragus hylocrius) is currently limited to a narrow, 400-km stretch of shola-grassland mosaic, from the Nilgiri Hills to the Ashambu Hills. At lower altitudes the tahr also use patches of grassland that grow on rock-sheeted substrates. Tigers, leopards (Panthera pardus), and wild dogs (Cuon alpinus) are the natural predators of Nilgiri tahr. However, the population decline of the tahr has been caused by heavy hunting pressure and habitat conversion. The largest population of tahr, estimated at 250-300 animals, now resides in the Grass Hills of the Anamalai Sanctuary.
The charismatic endangered lion-tailed macaque (Macaca silenus) and Nilgiri macaque (Semnopithecus johnii) are other endemic species that need intact habitat and are highly threatened by habitat conversion. This ecoregion also harbors India’s largest Asian elephant (Elephas maximus) population and contains critical habitat for tigers (Panthera tigris). The survival of the tiger and elephant is threatened by habitat fragmentation. Among the other threatened species are the sloth bear (Melursus ursinus), gaur (Bos gaurus), and wild dog.
Endemic and Near-Endemic Bird Species (an asterisk signifies that the species’ range is limited to this ecoregion)
- Columbidae Columba elphinstonii
- Bucconidae Ocyceros griseus
- Corvidae Dendrocitta leucogastra
- Turdidae Brachypteryx major
- Pycnonotidae Pycnonotus priocephalus
- Timaliidae Garrulax jerdoni
- Timaliidae Turdoides subrufus
- Muscicapidae Ficedula nigrorufa
- Muscicapidae Eumyias albicaudata
- Sylviidae Schoenicola platyura*
- Timaliidae Garrulax cachinnans*
- Motacillidae Anthus nilghiriensis*
- Psittacidae Psittacula columboides
The broad-tailed grassbird (Schoenicola platyura) and Nilgiri pipit (Anthus nilghiriensis) are high-elevation grassland species. The high endemism levels seen among the mammals and birds extend to other taxonomic groups as well. About 90 of India’s 484 reptile species are endemic to these forests, including eight endemic genera (Brachyophidium, Dravidogecko, Melanophidium, Plectrurus, Ristella, Salea, Teretrurus, and Xylophis). The amphibian fauna exhibits even greater levels of endemism: almost 50 percent of India’s 206 amphibian species are endemic to this ecoregion, among which are six endemic genera (Indotyphlus, Melanobatrachus, Nannobatrachus, Nyctibatrachus, Ranixalus, and Uraeotyphlus).
Protected Areas That Overlap with the Ecoregion
- Mukurty National Park
- Silent Valley
Among these, Periyar, Anamalai, and Kalakad-Mundanthurai represent three important reserves. Parambikulam, Anamalai, and Eravikulam lie adjacent to each other and form a large protected area complex that harbors important Nilgiri tahr populations. Four reserves-Periyar, Anamalai, Eravikulam, and Megamalai (proposed) – extend into the adjacent South Western Ghats Moist Deciduous Forests. The threats to this ecoregion’s natural habitats and biodiversity are manifold. Some of the major threats include conversion of forests into tea, coffee, potato, teak, Eucalyptus, and cardamom plantations, as well as road construction, tourism pressures, and livestock grazing. Illegal taking of timber is high and is considered a major threat to the remaining forests. Many people own guns for crop protection that they also use for poaching.
The Nilgiri and Cardamom Hills in particular harbor high levels of richness and endemism as well as some of the most important populations of elephants and tigers. These areas are especially affected by the tea, coffee, and rubber plantations. Shifting cultivation has begun to clear patches of old-growth forest. In the Anamalais, fig trees from the sholas are felled or lopped to feed camp elephants. Because many of these species are dioecious, this affects the sexual selection among trees and causes reproductive isolation. Fig trees are also keystone food resources for several species, and their removal results in cascading ecological effects on the frugivore community. Hydroelectric power development along the rivers in this ecoregion is also a serious threat. In addition to inundating critical habitat, dam construction also causes tremendous habitat destruction and disturbances. The mountains, especially in the south, are mineral-rich. Therefore, mining is a potential future threat that should be addressed with preemptive measures.
Image Attribution: The image above, sourced from Wikimedia Commons, shows a photograph of the Lion Tailed Macaque (Macaca silenus). Like many others, it is endemic to the montane forests of the Western Ghats. It was uploaded by Mr. Uday Kiran.