Climate change destabilising Western Ghats’ forest ecosystems in Nilgiri Biosphere Reserve

Environment & Ecology · 24 August 2026 · Based on The Hindu (original report)

2-minute summary

A scientific study titled 'Mapping forest phenological shift in Nilgiri Biosphere Reserve, Western Ghats: Response to Climate Change' reveals that climate change is severely destabilising the forest ecosystems of the Nilgiri Biosphere Reserve (NBR). Analyzing satellite data from 2000 to 2020, researchers recorded an annual temperature increase of 0.01°C and a rainfall decrease of 3.97 mm per year between 1950 and 2018. These climatic changes have disrupted the phenological cycles—the timing of biological activities like greening and shedding—across moist deciduous, dry deciduous, semi-evergreen, and wet evergreen forests. While the 'Start of Season' (SOS) delayed between 2001 and 2010, it advanced between 2011 and 2020, indicating erratic seasonal rhythms. Crucially, the high-altitude tropical montane 'Shola' forests are losing their self-contained, humid microclimates, causing mosses, orchids, and ferns to dry up. This ecological shift threatens the region's biodiversity and water security, necessitating immediate adaptive conservation strategies.

Why it's in the news

A 2024 study published in the peer-reviewed journal 'Remote Sensing' has warned that climate change is causing erratic phenological shifts and destabilising native forest ecosystems, particularly the sensitive Shola forests, within the Nilgiri Biosphere Reserve of the Western Ghats.

Background and context

The Nilgiri Biosphere Reserve (NBR), established in 1986, was India's first biosphere reserve under UNESCO's Man and the Biosphere (MAB) Programme. Spanning across Tamil Nadu, Kerala, and Karnataka, it represents a critical biodiversity hotspot within the Western Ghats. The reserve features a unique altitudinal gradient hosting diverse forest types, including dry deciduous, moist deciduous, semi-evergreen, wet evergreen, and the high-altitude Shola-grassland complex. Shola forests are tropical montane forests found in valleys separated by rolling grasslands. They act as natural 'sponges' that retain rainwater and feed perennial South Indian rivers like the Bhavani, Moyar, and Kabini. Historically, Sholas maintained a highly stable, cool, and humid microclimate independent of external weather. However, rising temperatures and declining rainfall are causing phenological shifts—changes in the timing of seasonal biological activities like leafing, flowering, and fruiting—which threaten to collapse these delicate, self-contained ecosystems.

Constitutional provisions

• Article 48A — Directive Principles of State Policy directing the State to protect and improve the environment and safeguard forests and wildlife.
• Article 51A(g) — Fundamental Duty of every citizen to protect and improve the natural environment including forests, lakes, rivers, and wildlife.

Committees and reports

• Western Ghats Ecology Expert Panel (Gadgil Committee) — Recommended designating the entire Western Ghats as an Ecologically Sensitive Area (ESA) to protect its fragile ecosystems from developmental pressures.
• High-Level Working Group on Western Ghats (Kasturirangan Committee) — Recommended a balanced conservation approach, designating 37% of the Western Ghats as ecologically sensitive to prevent environmental degradation.

Government schemes

• National Mission for a Green India (GIM) — Aims at protecting, restoring, and enhancing India's forest cover and responding to climate change through adaptation and mitigation measures.
• Biosphere Reserve Scheme — Provides financial assistance for conservation, research, and monitoring activities in designated biosphere reserves across India.

International organisations

• UNESCO Man and the Biosphere (MAB) Programme — Promotes scientific cooperation and research to conserve biodiversity and manage biosphere reserves sustainably; NBR is a designated site under this network.

Previous UPSC questions on this theme

• Prelims GS-1 2019 — Which of the following are in Agasthyamala Biosphere Reserve? (a) Neyyar, Peppara and Shendurney Wildlife Sanctuaries; and Kalakad Mundanthurai Tiger Reserve (b) Mudumalai, Sathyamangalam and Wayanad Wildlife Sanctuaries; and Silent Valley National Park (c) Kaundinya, Gundla Brahmeswaram and Papikonda Wildlife Sanctuaries; and Mukurthi National Park (d) Kawal and Sri Venkateswara Wildlife Sanctuaries; and Nagarjunasagar-Srisailam Tiger Reserve

Mains practice: Analyze the ecological impact of climate change on the Nilgiri Biosphere Reserve, with special reference to phenological shifts and the vulnerability of Shola forests.

The Nilgiri Biosphere Reserve (NBR), a critical biodiversity hotspot in the Western Ghats, is facing severe ecological destabilization due to climate change. A recent study (2024) highlights that the region experienced a temperature rise of 0.01°C/year and a rainfall decline of 3.97 mm/year (1950–2018), triggering unprecedented changes in forest dynamics.

**Ecological Impacts on the NBR:**

• **Phenological Shifts:** Climate change is altering the timing of biological activities (Start, End, and Length of growing seasons) across moist deciduous, dry deciduous, semi-evergreen, and wet evergreen forests. Between 2001 and 2010, the growing season delayed, whereas between 2011 and 2020, it advanced. This unpredictability disrupts plant-pollinator synchronization and food availability for herbivores.

• **Degradation of Shola Forests:** High-altitude tropical montane Shola forests are losing their unique self-contained microclimates. The cool, humid conditions inside these pockets are drying up, leading to the yellowing of vegetation and a decline in epiphytes, mosses, ferns, and orchids.

• **Water Security Threats:** Shola forests act as natural hydrological sponges. Their degradation directly threatens the perennial water supply to major South Indian rivers, impacting downstream agriculture and human settlements.

• **Invasive Species and Fire Risks:** Warmer, drier microclimates facilitate the spread of invasive exotic species (like Acacia and Eucalyptus) and increase the frequency of forest fires, further fragmenting the native ecosystem.

**Conclusion:**

To safeguard the NBR, conservation strategies must transition from static protection to active, climate-resilient restoration. This requires continuous satellite monitoring of phenological shifts, eradication of invasive species, and restoring the microclimate of degraded Shola fragments to preserve this vital ecological heritage.

Prelims practice questions

Q1. With reference to the Nilgiri Biosphere Reserve (NBR), consider the following statements: 1. It was the first biosphere reserve established in India. 2. It encompasses parts of Tamil Nadu, Kerala, and Karnataka. 3. The unique Shola forests found here are high-altitude temperate coniferous forests. Which of the statements given above are correct?

1. 1 and 2 only
2. 2 and 3 only
3. 1 and 3 only
4. 1, 2 and 3

Answer: A. Statements 1 and 2 are correct. Statement 3 is incorrect because Shola forests are high-altitude tropical montane wet temperate/broadleaf forests, not coniferous forests.

Q2. In the context of forest ecology, the term 'Phenology' is best described as:

1. The study of soil micro-organisms and their nutrient cycling capacity.
2. The genetic modification of forest species to make them climate-resilient.
3. The process of mapping forest canopy cover using high-resolution satellite imagery.
4. The study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate.

Answer: D. Phenology refers to the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life (such as flowering, leafing, and migration).

Q3. Which of the following rivers receive water from the hydrological systems of the Nilgiri Biosphere Reserve?

1. Narmada and Tapti
2. Mahanadi and Subarnarekha
3. Bhavani and Kabini
4. Godavari and Krishna

Answer: C. The Nilgiri Biosphere Reserve feeds major perennial rivers of South India, including the Bhavani, Moyar, and Kabini (which are tributaries of the Cauvery river system).

Revision flashcards

• What are Shola forests? High-altitude tropical montane wet temperate forests found in the valleys of the Western Ghats, separated by rolling grasslands.
• In which year was the Nilgiri Biosphere Reserve established, and which states does it span? Established in 1986; it spans Tamil Nadu, Kerala, and Karnataka.
• What is 'Phenology' in the context of climate change studies? The study of the timing of recurring biological events (e.g., leafing, flowering, fruiting) in response to environmental drivers like temperature and rainfall.
• According to the 2024 study on NBR, what were the long-term annual temperature and rainfall trends between 1950 and 2018? Temperature increased by 0.01°C per year, and average rainfall decreased by 3.97 mm per year.
• Why are Shola forests considered hydrological sponges? They possess high water-retention capacity, slowly releasing water to feed perennial streams and rivers in Southern India.