Mud Records Reveal 3,300-Year Climate Story Behind Kaziranga’s Rhino Stronghold

Kaziranga National Park—part of the Indo-Burma biodiversity hotspot and a UNESCO World Heritage Site—stands out as a rare stronghold for megafauna, especially the Indian one-horned rhinoceros.

Hidden beneath the wetlands of Assam’s Kaziranga National Park (KNP), layers of ancient mud have preserved a remarkable ecological record—one that explains why the Indian one-horned rhinoceros survived in the Northeast while vanishing from much of the subcontinent.

In a pioneering palaeoecological study, scientists from the Birbal Sahni Institute of Palaeosciences (BSIP), an autonomous institute under the Department of Science and Technology (DST), have reconstructed the first long-term record of past vegetation, climate change and herbivore activity from Kaziranga, using pollen and fungal spores preserved in wetland sediments.

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Kaziranga: A Refuge in a Changing World

Rapid urbanisation, deforestation, industrialisation, and extreme natural events such as floods and droughts are driving biodiversity loss worldwide. These pressures are particularly concerning for megaherbivores, with nearly 60% of large herbivore species globally now threatened, and Southeast Asia emerging as the most at-risk region.

Kaziranga National Park—part of the Indo-Burma biodiversity hotspot and a UNESCO World Heritage Site—stands out as a rare stronghold for megafauna, especially the Indian one-horned rhinoceros.

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Reading History from Wetland Mud

To uncover how this refuge evolved, researchers extracted a sediment core over one metre long from the Sohola swamp inside Kaziranga. Each layer of mud functions as a natural time capsule, preserving:

• pollen grains, revealing past vegetation types, and

• coprophilous fungal spores, which grow on animal dung and act as indicators of herbivore presence and activity.

This innovative approach allowed scientists to reconstruct palaeovegetation and palaeoherbivory patterns spanning the last ~3,300 years.

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From Forests to Grasslands: A Shifting Landscape

The study, published in the international journal Catena (Elsevier), shows that Kaziranga’s present grassland-dominated landscape is very different from its past.

Key findings indicate:

• Early phases were marked by denser forests and deeper swamp conditions, with lower wildlife activity.

• Over time, shallower wetlands and more open vegetation emerged, supporting increased megaherbivore activity, including rhinos.

• These ecological transitions were shaped by climate fluctuations, vegetation shifts, invasive species, and grazing pressure.

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Why Rhinos Disappeared Elsewhere

Crucially, the research documents the regional extinction of megaherbivores, including the Indian rhinoceros, from northwestern India during the late Holocene.

The decline is linked to:

• Climatic amelioration and instability, particularly during the Little Ice Age, and

• Rising human pressures, including habitat loss and overhunting.

In contrast, northeastern India remained relatively climatically stable, with lower anthropogenic disturbance. This stability enabled eastward migration of rhinoceroses, leading to their eventual concentration in Kaziranga, where conditions remained favourable for survival.

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Lessons for Conservation in a Warming World

The study provides rare, long-term evidence showing how climate and vegetation changes directly influence wildlife migration, survival and extinction. It confirms that the Indian one-horned rhinoceros was once widely distributed across the Indian subcontinent, before its range dramatically contracted during the Holocene.

By revealing how ecological resilience and climate stability helped Kaziranga emerge as a megafaunal refuge, the findings offer valuable insights for:

• climate-adaptive conservation planning,

• habitat restoration, and

• long-term wildlife management under future climate change scenarios.

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Science Backing Conservation Policy

Supported by the Department of Science and Technology, the research underscores the importance of palaeoecological studies in informing modern conservation strategies.

The paper is titled:“Late Holocene palaeovegetation and palaeoherbivory dynamics from Kaziranga National Park, Northeast India”and is available at: https://doi.org/10.1016/j.catena.2025.109762