The highest elevations of the Western Ghats have some of the most spectacular landscapes in southern India. These mountain-tops (above 1400 m) have unique habitats called shola, which are also called montane evergreen or cloud forests. Unlike lowland forests that are often long, continuous stretches, these forests are naturally patchy, with the patches separated by natural grasslands; the forest patches are usually in the valleys of rolling hills on these mountain-tops. This natural matrix of forests and grasslands is evolutionarily adapted only to mountain-tops. For the many bird and animal species that live exclusively in these shola habitats, it is as if these mountain-tops are islands in the sky, otherwise known as ‘sky islands’. Like oceans that isolate regular islands, the valleys between sky islands contain drier habitats and act like the hostile oceans for these wet-cool-habitat-adapted species.
The shola sky islands are found from the south of Baba Budan Hills in Karnataka, roughly 15 deg. N. There are many isolated islands; some in Karnataka and northern Kerala are fairly small, measuring only about 10-20 sq.km, while other larger islands like Nilgiris and Anamalai-Palani Hills are about 1500 sq.km. Farther south, the ‘high-wavies’ (Meghamalai) and the Ashambu Hills (Agasthyamalai) are again much smaller.
How were they formed?
The Western Ghats is a very old mountain chain, unlike the newly formed but taller Himalayas (< 50 million years old). The mountains of the southern Western Ghats were formed by tectonic activity as the Indian subcontinent drifted from Gondwana to hit the Asian plate, some 150 million years ago. The northern Western Ghats, on the other hand, were formed largely by volcanic activity. This is one of the reasons why the southern Western Ghats are taller, forming the montane shola sky islands. Over a shorter time scale, climate – wet and cold in this landscape – impacted the shola habitat. So, for any life form living on the mountain, climate and mountain structure (topography) interact to provide this unique habitat on mountain-tops, isolated by low-elevation, drier-habitat valleys. This isolation has resulted in the diversification of some birds. In the erstwhile Shorwings [now Sholakilli (Sholicola)] and Laughing Thrushes [now Chilappan (Montecincla)], there have been endemic radiations of three and four species in each of these genera, only on the sky islands.
Centre of endemism
One of the unique patterns of diversity on the shola sky islands, and in fact on any sky island, is that these areas are not very species-rich, but are very high in endemism. Species found on these sky islands are especially adapted to these habitats and are often ancient lineages. This implies that the species in these habitats are very old. This is because of the interplay of elevation and ancient climate. Coastal mountain-tops like the Western Ghats’ shola sky islands have stable climates (over thousands of years), unlike the lower elevations that alternate between wet and dry. Therefore species living on the tops of these mountains survived through severe climatic fluctuations like the ice ages. The Sholicola Shortwings or Sholakilli have lived on these mountains for millions of years – about 9 million years – and have not crossed deep valleys like the Palghat Gap for about 5 million years. To put this in perspective, the age of modern human species is only about 0.2 million years, the entire Homo genus evolved only 2.5 million years ago, and the tiger is under a million years old. All of this means that the species we see on these mountain-top sky islands are very special, and there need to be stronger efforts to conserve them.
Where in Karnataka?
The high elevation areas of Karnataka that share a border with Kerala host the northern-most islands of the shola sky island system. These northern sky islands, like the Baba Budan Hills, form the northern-most limit of some endemic species. For species like the newly described genus Sholicola, Baba Budan perhaps forms the global distribution limit. The number of individuals of the Sholicola is very low, and these low densities mean that a sighting of this bird here is more valuable than of the same species in another area like in the Nilgiris. The chances of the population of this species going extinct are also larger from these lower hills.
The shola forest habitats have been conserved in various areas, largely in Tamil Nadu and Kerala. The Karnataka part of the landscape has very little shola habitat, and large parts of these have been conserved as parts of existing protected area networks. Over the last century, a large part of the overall shola habitat was modified to establish plantations, especially tea and timber. In Baba Budan Hills, some of these habitats were historically converted to coffee plantations. Today, it may be safe to say that large-scale conversions of shola forests have stopped. Some of the challenges to forest conservation today are from invasive species and forest degradation. There are also challenges due to forest fragmentation from past deforestations.
The scenario with grasslands, also natural habitats in the shola matrix, is somewhat more challenging. Research with my collaborators indicates that a large part of the grasslands (between 60-70%) has been modified over the last 3 to 4 decades. A large part of this conversion has been to timber plantations. In the previous century, timber plantations of Acacia, Eucalyptus, and Pine were planted as a source of pulp and firewood. Soon after the harvesting or cutting of trees was prohibited by a Supreme Court order, this activity stopped. However, Acacia is a known invasive species, and plants from existing plantations continue to invade into grasslands, converting large areas into plantations. This is one of the largest conservation challenges in this landscape.
Like most mountain-tops, the shola sky islands also face considerable threats from anthropogenic climate change. Other researchers have shown that several bird species distributions have spread from lower elevations to the mountain-tops, since the times of Dr. Salim Ali’s surveys. This implies that competition for resources on the mountain-tops is increasing. The species that are highly specialised and adapted to the tops of these sky islands have nowhere else to go. Unfortunately, it is the grasslands that are threatened with the greater probability of extinction, since forests are predicted to increase.
Coffee and diversity
One of the interesting facts about Baba Budan Hills is that it is thought to be one of the earliest centres of coffee cultivation in India. Much of the coffee in these parts is grown under native shade trees, and is known as shade coffee. Due to this natural canopy cover, a number of birds and animals can be found in these coffee estates.
In summary, the shola sky islands are a wonderful habitat, with scenic landscapes and several ancient species that have survived for millions of years. These endemic species have evolved on these isolated mountaintops, and Baba Budan Hills offers excellent accessibility of the entire hill range, and provides a great opportunity to enjoy this diversity.
Reaching Baba Budan Hills
The River Tern Lodge of Jungle Lodges is at the foothills of Baba Budan Hills. One could get up on the hills from the River Tern Lodge, visit the horticulture department at Kemmangundi, and visit the Baba Budan peak. Just before getting off the crest, one can also go up the Mullayangiri peak – the tallest peak in Karnataka. This drive takes you through the shola forest-grassland matrix. What sets this location apart from other areas is the wonderful access to most of the C-shaped hills; there is a good road that takes you all along most of the crest, very close to the tallest mountains. So, this is a great location for an entire family to experience the shola sky islands quickly and easily, compared to some other sky island locations that require several hours of trekking.