Species loss hastened by climate change

Palaeo climate research shows that past global warming events triggered significant ecological changes, favouring deciduous forests over evergreen ones, according to an analysis by Mongabay-India (MI).

The analysis highlights a recent discovery of fossil evidence of a tree species now considered endemic to the Western Ghats, in a coalfield in the state of Assam in India, saying it sends a clear message. If global warming continues at its current pace, earth risks losing or severely restricting many of its precious taxa.

The MI analysis states that 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 abstract of the study points out that endemism, driven by geological and climatic transformations, is a hallmark of biodiversity hotspots. Fossil evidence offers unique insights into the historical biogeography and evolutionary trajectories of endemic taxa, particularly in biodiversity-rich regions like northeast India and the Western Ghats. As per the study, regions with high concentrations of endemic species are designated as biodiversity hotspots by Conservation International (CI). Of the 36 global hotspots identified by CI, four are in India: the Eastern Himalaya, Indo-Burma, Western Ghats, and the Andaman and Nicobar Islands.

This study highlights a significant biogeographic shift in the distribution of the species over millions of years. Fossil evidence from northeast India suggests that the genus once had a much broader range during the late Paleogene, thriving under equable climatic conditions like those found in its present habitat in the Western Ghats. However, subsequent climatic and geological changes likely led to its extinction from northeast India, confining the species to its current distribution in the Western Ghats. This raises critical questions about the palaeogeographic and climatic conditions that supported these taxa in northeast India during the late Oligocene.

Researchers quoted in the MI report say 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 6000 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. Experts add that as a long-term strategy for preserving these species, it is crucial that we prioritise conservation of evergreen forests. They make a strong case for conserving natural forests as otherwise we would lose something that has survived ice ages, continental drift, and climatic upheaval

As the MI analysis points out India’s landmass has undergone a dramatic latitudinal shift while migrating from the southern to the northern hemisphere, traveling approximately 9000 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. 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 may not survive the test of global warming. 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.