- The discovery of fossilised leaves of a species endemic to Western Ghats, in Assam coalfields, suggests that the taxa likely migrated southwards in response to the temperature shift caused by uplift of the Himalayas.
- Palaeoclimate research shows that past global warming events triggered significant ecological changes, favouring deciduous forests over evergreen ones.
- A similar shift is projected under current carbon dioxide rise, threatening many evergreen species with extinction.
The recent discovery of fossil evidence of a tree species now considered endemic to the Western Ghats, in a coalfield in Assam, sends a clear message: if global warming continues at its current pace, earth risks losing or severely restricting many of its precious taxa.
Scientists from the Birbal Sahni Institute of Palaeosciences unearthed fossilised leaf remains of Nothopegia oligo travancorica and Nothopegia oligo castaneifolia, in the Makum coalfields of Assam. The “oligo” in the name stands for the geologic time period Oligocene, or the period of time when a fossil was formed, dating back approximately 24 million years. The findings of the study suggest that these species, once widespread across northern and northeastern India, gradually migrated and found refuge in the Western Ghats, where they have since persisted in pockets.
The lead researcher Gaurav Srivastava elaborates, “Our research revealed that historically, these species were distributed across north and northeastern India — from Assam to Darjeeling — but migrated southwards over time. The primary driver was the decrease in cold-month mean temperatures following the uplift of the Himalayas.” The Himalayan uplift history suggests that the mountains gained most of their elevation around 11 million years ago — rising from approximately 6,000 metres to their current height of about 8,848 metres.
During this shift in elevation, species that could not adapt to the substantial drop in temperature in the winters migrated towards the Western Ghats, which maintained the warm, stable temperatures these evergreen species required. While migration for plant species happens through seed dispersal by wind, animals, or birds, the survival depends on the suitability of climatic conditions at the destination. “Several other taxa, such as Holigarna and Poeciloneuron, show similar patterns,” Srivastava says. This, according to the researchers, emphasises the critical role of low-latitude, warm-climate refuges like the Western Ghats in preserving biodiversity.
Specialist in forest ecology and phytogeography and former director of research at French Institute, Pondicherry, B.R. Ramesh, informs Mongabay India that several species that were once widely distributed across India, are now confined to the Western Ghats. “One example is the Dipterocarpaceae family, which is dominant in Southeast Asia. Some of the Fossils of Dipterocarps have been found in central and northern India, but today, their living species are found only in humid zones of the Western Ghats and northeast India. This suggests significant climatic shifts — likely warming and drying — that led to local extinctions in those regions,” he says.
Explaining the genus Nothopegia, now severely restricted to certain areas in the Western Ghats, Ramesh says, “The current Nothopegia travancorica is an understorey tree, about five-to-eight-metres tall, with a very localised distribution in the Western Ghats.” Nothopegia finds mention in the book Atlas of Endemics of the Western Ghats (India), co-authored by Ramesh, that identifies the field records of each endemic tree species alongside forest types, elevation range and length of the dry season. “This data shows where exactly the species has been recorded,” he says. The plant species are now found in places like Ratnagiri in Maharashtra, Panaji in Goa, Palakkad and Thiruvananthapuram in Kerala, the paper reports.
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Past lessons of change
India’s landmass has undergone a dramatic latitudinal shift while migrating from the southern to the northern hemisphere, traveling approximately 9,000 kilometres over a period of about 140 million years, and later colliding with the Eurasian Plate, impacting both terrestrial and marine lives as well as the climate patterns. Srivastava points to this unique tectonic history of the landmass, which makes its geology and ancient flora crucial for palaeontology as well as future climate analysis and outcomes. “The collision of the Indian and Eurasian Plates gave rise to the Himalayas, which play a vital role in driving the South Asian monsoon and modulating the global climate system. These factors make India’s palaeo scientific research of immense value to the global scientific community,” Srivastava shares.
In a previous study, Srivastava and team looked at Eocene Thermal Maximum 2 (ETM2) — one of the two well-studied hyperthermal events, the other one being Paleocene-Eocene Thermal Maximum (PETM) — occurred around 54 million years ago, as an analog to understand the consequences of high atmospheric CO₂ on equatorial hydrology and vegetation.
They found that during ETM2 that lasted around 15,000 years, when atmospheric CO₂ exceeded 1000 ppm, there was a significant decrease in rainfall near the paleo-equator. “This reduction in rainfall led to a marked expansion of deciduous forests at the expense of evergreen forests,” he says. Deciduous taxa, adapted to longer dry seasons, became more dominant, indicating a shift toward more seasonal, drier conditions, according to the study.
“Today, with CO₂ levels rising sharply (by over 100 ppm in the last 57 years) and projections suggesting they will again exceed 1,000 ppm by the end of the 21st century, a similar ecological shift is predicted where deciduous forests dominate, resulting in the extinction of many evergreen forest species,” Srivastava points out.
Conservation strategy
The fossil remains of many ancient species like Sivapithecus, an early primate and human ancestor that once lived in the Shivalik hills, suggest they went extinct when evergreen forests were replaced by deciduous ones — again showing how drastic environmental changes can trigger extinctions, he highlights. If climate history repeats, there is a good chance that evergreen species like mango (Mangifera indica) may not survive the test of global warming.
As a long-term strategy for preserving these species, says Srivastava, it is crucial that we prioritise conservation of what is left of the evergreen forests. Anupama Krishnamurthy, a researcher at the Laboratory of Palynology & Paleoecology, French Institute of Pondicherry, says the paper makes a strong case for conserving natural forests. “This research reminds us that ecosystems like those in the Western Ghats are products of millions of years of evolution and environmental history. You can’t recreate that with afforestation drives. Losing these forests means losing something that has survived ice ages, continental drift, and climatic upheaval — until now,” she says.
While anthropogenic pressure causes rapid and visible degradation of forest cover, climate change acts more slowly. However, it could potentially intensify temperatures and dry conditions, making the environment unsuitable for many evergreen species. “Three different patterns have been observed in the way species respond to climate change — migration, where they move in search of more suitable habitats; contraction, where the species’ ranges shrink; and stability, where certain regions remain unchanged and continue to support the same species over long periods,” says Ramesh, highlighting the importance of conserving regions like the Western Ghats that supports high level of endemism.
“These stable areas are crucial. They serve as gene pools that may allow species to diversify or adapt in response to future climate changes. Unfortunately, only 28% of these stability zones fall within India’s protected area network. The rest are outside it,” he adds.
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Banner image: Study authors conducting field work at the Makum coalfield in Assam. Image courtesy of Harshita Bhatia.
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