The Unusual Threat of Trees to India’s Open Ecosystems

While increasing tree cover is typically viewed as a positive step for biodiversity conservation and climate change mitigation, it can have unintended consequences if implemented in areas historically characterised by different habitats, such as grasslands and savannas.

Recent Findings

• A study published in the journal Global Change Biology, reported that increasing tree cover in open ecosystems, such as savannahs and grasslands, has substantially reduced the number of native grassland birds. 
• Specifically, in the African Savannah, the population of grassland birds has declined by more than 20% due to the proliferation of trees in these historically open habitats.

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Open Ecosystems

• About: Open ecosystems are environments such as savannas, grasslands, and shrublands characterised by a continuous ground-layer of grasses with minimal or low tree cover. In some areas, trees, herbs, and shrubs can coexist. 
  • The composition and structure of vegetation in these ecosystems are closely linked to broader environmental conditions. 
• Location: Savannas and grasslands cover more than half of Earth’s land surface area, ranging across tropical, subtropical, and temperate realms. 
  • Grasslands and Savannahs are found in tropical and temperate regions worldwide.
  • They cover nearly 40% of the earth’s total landmass.
• Characteristics of Open Ecosystems: Open ecosystems, such as grasslands and savannahs, are characterised by a grassy understory and a scattering of native tree species. These habitats are generally maintained by specific natural and human activities.
• Significance of Open Ecosystems
  • Biodiversity: Open ecosystems are home to distinctive and ancient biodiversity, contributing to the planet’s ecological richness.
    • Home to many endemic and at-risk species of plants and animals.
    • Host megaherbivores like elephants, rhinoceroses, and buffaloes in Africa and Asia.
    • Support grassland birds such as bustards, floricans, and grouse in the Himalayan grasslands and American prairies.
  • Ecosystem Services:
    • Climate Regulation: Vegetation in these ecosystems plays a key role in regulating the earth’s climate.
    • Water Management: They help maintain water quantity and quality.
    • Carbon Storage: Open ecosystems store carbon both below-ground and above-ground.
    • Resource Provision: They provide essential resources such as food and fuel.
  • Cultural and Economic Value:
    • Historical Significance: Humans first evolved in the grasslands and savannas of Africa, and Indigenous peoples worldwide have shaped these ecosystems through practices like fire and animal management.
• Current Threats: Rapid loss of these open ecosystems is occurring globally.
  • Primary Threats: Conversion of grasslands to other land uses, Intensive agriculture, Loss due to erosion, Large-scale development projects and Overgrazing.
  • Unusual Threats: Woody Encroachment is an unusual threat.

About Woody Encroachment

• Woody Encroachment is a phenomenon where woody plants gradually increase in abundance within grasslands, savannas, and other open ecosystems. 
• This shift occurs as these woody plants outcompete and replace grasses,and other herbaceous vegetation. 
• Over time, this process transforms open, grassy landscapes into more closed, densely vegetated areas. 

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Reasons for Woody Encroachment: Threat to Open Ecosystems

• Disturbance in Disturbance Regimes: Disturbance regimes are natural and human activities that maintain the balance of open ecosystems. 
  • These include grazing by herbivores, which limits tree growth, and periodic fires, which prevent trees from overgrowing.
  • When disturbance regimes are disrupted, trees can establish themselves more easily. 
    • This disruption accelerates the process of woody encroachment, further converting diverse, multi-layered ecosystems into uniform layers of woody plants. 
    • This shift poses a significant threat to the biodiversity and ecological health of open ecosystems.
• Invasive Species: The introduction of invasive woody species can accelerate encroachment, outcompeting native grasses and forbs. Examples of India include:
  • Prosopis juliflora: Planted in the Banni grasslands by the Gujarat Forest Department from 1961 to combat desertification and provide firewood, it has since transformed large areas into Prosopis woodlands.
  • Eucalyptus and Malabar Silk-Cotton: In the Shola grasslands, eucalyptus plantations have spread rigorously, whereas the Malabar silk-cotton tree has been running riot in the wet terai grasslands of the Himalaya.
• Global Drivers of Woody Encroachment
  • Woody encroachment is widespread worldwide. Many studies have unearthed evidence of different drivers of encroachment in different continents. 
  • South America: Fire suppression and habitat fragmentation are the main drivers of woody encroachment.
  • Australia and Africa: Increased CO2 levels and variations in rainfall contribute significantly to woody encroachment. The Effects of Increased CO2 on Woody Encroachment are as follows: 
    • Carbon Dioxide Effect: Higher atmospheric CO2 levels, due to climate change, encourage the proliferation of deep-rooted woody plants in grasslands.
    • Photosynthetic Pathway: Trees, which use the C3 photosynthetic pathway, benefit from increased CO2, leading to their dominance over grasses.
    • Suppression of Grasses: Once trees become dominant, they can further suppress grasses through shading and reduced fire frequency.

Effects of Woody Encroachment on Ecosystems and Biodiversity

• Homogenisation of Ecosystems: The increase in tree and shrub cover are converting open habitats into those with greater tree/shrub density
  • This Leads to homogenization of ecosystems, turning diverse, multi-layered habitats into uniform layers of woody plants
• Grassland Bird Declines:
  • Study in Southern Africa: In South Africa, Eswatini, and Lesotho, data from the ‘South African Bird Atlas Project 2’ revealed significant declines in open ecosystem birds.
  • Findings: Of 191 species analysed between 2007 and 2016, 121 showed declining population trends. 
    • Notably, the decline of 34 species was linked to woody encroachment.
• Impact on Soil and Vegetation:
  • Soil Changes: Succession of woody species alters soil conditions.
  • Grass Species: Changes in soil conditions affect grass species composition.
• Effects on Fauna:
  • Birds: Woody species increase predation risk, particularly affecting specialist birds’ nests. 
  • Rodents: In the Banni grasslands of Kutch, woody encroachment reduced the population of grassland specialist rodents. 
    • These species faced increased predation risk and spent more time on vigilance rather than foraging due to the encroachment of trees.

Other Threats to Open Ecosystems

• Eurocentric and Forest-Centric Perspectives:
  • Historical Context:
    • Colonial Policies: Colonial officers viewed open ecosystems as “wastelands” that should be replaced with timber-producing trees.
    • There is also a prevalence of Eurocentric view that prioritises dense tree cover, leading to the misconception that open ecosystems are ‘degraded’ without it.
• Land Conversion: Increasing pressures from land conversion activities pose significant threats to open ecosystems. The forest policies also led to the conversion of grasslands to plantations and criminalised traditional practices such as grazing and fire management.
• Focus on Climate Change:
  • Carbon Sequestration: Today, the emphasis is on trees as sources of carbon sequestration, with open ecosystems often viewed as obstacles to this goal.
    • Focus on Tree Addition: Many contemporary restoration projects prioritise adding trees, which may not align with the ecological needs of grasslands and savannas.
• Inadequate Restoration Approaches:
  • Essential Features and Processes: Effective restoration of open ecosystems requires maintaining key features and processes such as fire and animal interactions, which are crucial for their assembly, functioning, and provisioning.

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Grasslands Across India

• About Grassland Ecosystem: A grassland ecosystem is a biome characterised by vast expanses of grasses, herbs, and occasionally some scattered trees or shrubs. Grasslands are found on every continent except Antarctica and can vary significantly in terms of climate, geography, and species composition.
• Diverse Climatic Regimes:
  • Arid Grasslands: Found in western India.
  • Floodplain Grasslands: Located in the Himalayan landscape.
  • Shola Grasslands: High-altitude grasslands in the Western Ghats.
• Biodiversity in the Himalayan Foothills:
  • Iconic Species: Includes Indian one-horned rhinoceroses, swamp deer, Bengal floricans, swamp grass babblers, and other endemic species.
• Threats to Grasslands
  • Fragmentation: Historical damage has broken these grasslands into fragmented patches.
  • Increased Vulnerability: Fragmentation makes these patches more susceptible to threats from surrounding forests, agriculture, and other human activities.
  • Woody Encroachment: As per the study of Indian Institute of Science Education and Research (IISER), Kolkata: Most of today’s wet grasslands occur inside protected areas such as national parks and sanctuaries. Yet woody encroachment is rampant inside these parks as well.
    • The cover of grassland habitats had shrunk by 34% while tree cover in these places had increased by 8.7%.

Suggestions to Protect Open Ecosystems

• Developing More Evidence on Woody Encroachment: There is a need to conduct comprehensive studies to better understand the adverse effects of woody encroachment on Open Ecosystems especially grassland biodiversity.
• Implement Long-Term Ecological Monitoring: using the gathered and available data to guide informed actions and policy changes regarding the management of grasslands.
• Address Terminological Issues
  • Reframe Terminology: There is a need to move away from colonial-era terms like “wastelands” that misclassify and undervalue open ecosystems.
  • Promote Accurate Classification: Adopt terminologies that reflect the true ecological value and importance of Open Ecosystems such as grasslands, supporting their conservation and appropriate use.

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