These stunted cloud forests exist only in sheltered valleys above 1,500m. Fragments separated by just 100m show distinct species compositions after centuries of isolation. Evolution observable between adjacent hilltops.
Chris huh, CC BY-SA 3.0, via Wikimedia Commons
Islands in the Sky
High in the Western Ghats of Southern India, a unique ecosystem exists, fragmented across mountaintops like an archipelago of islands in the sky. These are the Shola forests, patches of stunted, evergreen tropical forest found only in sheltered valleys at elevations above 1,500 meters, surrounded by a sea of montane grasslands. This entire mosaic, dating back at least 20,000 years, forms a natural laboratory for studying evolution. The isolation exists between major mountain ranges separated by deep breaks like the 40-kilometer-wide Palghat Gap, but also between adjacent forest patches on the same massif.
This landscape of natural fragmentation has been intensified by human activity over the last century, with vast tracts of grassland converted to tea, coffee, and timber plantations. This leaves the Shola patches more isolated than ever, restricting gene flow for species that cannot or will not cross the modified landscape. For many forest-dwelling organisms, a few hundred meters of open grassland or tea plantation is as effective a barrier as a wide ocean, led to for divergent evolution.
Evolution in Real Time
The Shola sky islands are a focal point for research into how species adapt and diverge in isolation. Studies led by biologist V.V. Robin have examined the genetics, songs, and physical traits of birds endemic to these forests. The White-bellied Sholakili (Sholicola albiventris), a small blue flycatcher, is a primary subject. Populations of this bird on different mountaintops, isolated for millions of years, show distinct genetic lineages and have developed unique song dialects.
Even more finely, the research demonstrates how bird populations in forest fragments on the same mountain, separated by only a few hundred meters of grassland, can show differences. These birds are reluctant to leave the cover of the forest understory, a behavior that severely limits movement between patches. This isolation leads to measurable genetic differentiation and vocal changes over surprisingly short distances. The work has been so significant it led to the reclassification of several bird groups, establishing two entirely new genera of songbirds endemic to the region: Montecincla (laughingthrushes) and Sholicola (flycatchers). These findings reveal the Western Ghats as a cradle of unique evolutionary history, with distinct species evolving in isolated pockets of high-altitude forest.
💡Fun Facts
The name "Shola" is derived from the Tamil word "solai," meaning a thicket or grove.
Shola forests act like massive sponges, absorbing monsoon rains and feeding numerous south Indian rivers, supporting millions of people downstream.
The Palghat Gap, a major break in the Western Ghats, is old enough to have allowed species on either side to evolve separately for millions of years.
Besides birds, the sky islands host other endemic and endangered species like the Nilgiri tahr (*Nilgiritragus hylocrius*) and the resplendent shrub frog (*Raorchestes resplendens*).
The Anamalai Tiger Reserve, which contains these habitats, is generally open from 6:00 AM to 6:00 PM.
Admission
Entry fees are approximately INR 30-80 for adults. Additional fees apply for vehicle safari, trekking, and cameras. Private vehicles are not permitted for safaris.
Accessibility
The terrain is mountainous and access to the shola forests typically requires guided treks on uneven paths. Safaris are available via forest department vehicles.
