TROPICAL FORESTS
1. Context
A small percentage of leaves on trees in tropical forests may be approaching the maximum temperature threshold for photosynthesis to work, suggests a study published in Nature.
2. Tropical Forests
- Tropical forests are diverse and complex ecosystems found in the equatorial regions of the world.
- They encompass a vast array of plant and animal species, making them one of the most biodiverse habitats on Earth.
- These forests play a crucial role in maintaining the planet's ecological balance, offering various ecological, environmental, and socio-economic benefits.
3. Characteristics
- Tropical forests are characterized by their high species richness, dense vegetation, and year-round warmth.
- They consist of several layers, including the emergent layer (tallest trees), canopy layer (dense foliage), understory layer (young trees and shrubs), and forest floor (decaying organic matter).
- The constant warmth and ample rainfall in tropical regions contribute to rapid growth and high levels of biological productivity.
- Tropical forests are biodiversity hotspots, housing an estimated 50-80% of the world's terrestrial species.
- This incredible diversity supports complex food webs and ecological interactions. From insects to mammals, birds to amphibians, these forests provide habitat for countless organisms, many of which are endemic and found nowhere else on the planet.
4. Carbon Reservoirs
- Tropical forests also play a critical role in global carbon cycling. The dense vegetation in these forests stores vast amounts of carbon, helping regulate atmospheric carbon dioxide levels and mitigate climate change.
- Through photosynthesis, trees absorb carbon dioxide and release oxygen, contributing to the planet's oxygen supply.
- These forests provide a multitude of ecosystem services. They regulate local and global climates, influence rainfall patterns, prevent soil erosion, and support water purification.
- They also offer cultural and economic value to indigenous communities and host ecotourism activities, contributing to livelihoods.
5. Threats and Conservation
- Despite their significance, tropical forests face numerous threats. Deforestation for agriculture, logging, mining, and urbanization has led to habitat loss and fragmentation.
- This threatens the survival of many species and disrupts ecosystem functions. Climate change poses additional challenges, including rising temperatures and altered precipitation patterns.
- Conservation efforts aim to mitigate these threats and preserve the unique biodiversity and ecological functions of tropical forests.
- Protected areas, sustainable logging practices, reforestation, and international agreements such as the Paris Agreement on climate change are crucial steps in ensuring the survival of these vital ecosystems.
6. Critical Temperature and Future of Tropical Forests
Estimation and Uncertainty:
- About 0.01% of leaves exceed critical temperature, but uncertainties persist in defining critical temperatures for tropical trees.
- Modelling indicates tropical forests can tolerate up to a 3.9°C temperature increase before potential tipping point.
Need for Action:
- Protection measures required to safeguard tropical forests from climate change impact.
- Uncertainties about critical temperature plasticity and leaf death's effect on tree death might alter predictions.
Climate Change Scenarios:
- 4°C temperature estimate aligns with the worst-case climate change scenario for tropical forests.
- Choices remain to determine the fate of these vital areas of carbon, water, and biodiversity.
Resilience and Thresholds:
- Previous studies show tropical forests' resilience to warming and drought effects on carbon uptake.
- Critical temperature functions as an upper limit, suggesting crossing the threshold is plausible within worst-case climate scenarios.
7. Impact of Deforestation and Climate Change on Tropical Forests
- Local Temperature Changes: Deforestation and fragmentation intensify temperature shifts alongside global warming.
- Critical Threshold Concern: The synergy of climate change and local deforestation might be pushing the hottest tropical forest areas close to or over the critical thermal threshold.
- Mitigation and Deforestation Reduction: Combining robust climate change mitigation efforts with decreased deforestation can safeguard vital carbon, water, and biodiversity domains from surpassing thermal critical limits.
- Importance of Tropical Forests: Tropical forests play a central role as carbon reservoirs and homes for global biodiversity.
- Sensitivity to Warming: These ecosystems are particularly sensitive to rising temperatures.
- Critical Temperature: A critical temperature around 46.7°C marks the point where photosynthetic processes in tropical trees begin to fail.
- Uncertain Leaf Temperatures: It's uncertain if the leaf temperatures experienced by tropical vegetation are approaching or will soon reach this threshold due to climate change.
8. Photosynthesis
- Photosynthesis is a fundamental biological process that sustains life on Earth by capturing light energy from the sun and converting it into chemical energy stored in the form of glucose and other organic molecules.
- This process takes place in the chloroplasts of plant cells and is critical for providing oxygen, food, and energy to both plants and the organisms that consume them.
Process Overview
Photosynthesis involves several complex steps that occur in two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle).
- Light-Dependent Reactions: These reactions occur in the thylakoid membranes of chloroplasts. Chlorophyll and other pigments absorb light energy, which is then used to split water molecules into oxygen and protons. Oxygen is released as a byproduct, while the protons are used to generate a proton gradient that powers the synthesis of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), energy-rich molecules.
- Calvin Cycle (Light-Independent Reactions): Taking place in the stroma of chloroplasts, the Calvin cycle uses the ATP and NADPH generated in the light-dependent reactions to convert carbon dioxide into glucose. This cycle involves a series of enzyme-catalyzed reactions that produce simple sugars and other organic compounds.
Importance
Photosynthesis is crucial for various reasons:
- Energy Source: It is the foundation of the food chain, as plants, algae, and some bacteria produce organic molecules that are consumed by herbivores and then passed up the trophic levels.
- Oxygen Production: Oxygen, released as a byproduct of photosynthesis, is essential for the respiration of organisms, including humans.
- Carbon Dioxide Regulation: Photosynthesis helps regulate atmospheric carbon dioxide levels by removing this greenhouse gas from the air and converting it into organic compounds.
- Energy Storage: Glucose and other organic molecules produced through photosynthesis store energy that can be used by plants for growth, reproduction, and other metabolic processes.
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For Prelims: Tropical forests, carbon cycling, climate change, Paris Agreement on climate change, Photosynthesis, chloroplasts of plant cells, ATP (adenosine triphosphate), NADPH (nicotinamide adenine dinucleotide phosphate), and Calvin Cycle.
For Mains: 1. Examine the significance of tropical forests as biodiversity hotspots and carbon reservoirs. Discuss the threats faced by these vital ecosystems, including deforestation, climate change, and habitat fragmentation. (250 words).
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Previous year Question1. Which of the following statements about tropical rainforests are correct? (UPSC CAPF 2021)
1. The soils of tropical rainforests are quite infertile.
2. The vegetation is evergreen, enabling photosynthesis to take place year around.
3. They have been described as 'deserts covered by trees'.
4. They are the most productive land-based ecosystem.
Select the correct answer using the code given below.
A. 2 and 4 only
B. 1, 3, and 4 only
C. 1, 2, and 3 only
D. 1, 2, 3 and 4
Answer: D
2. "If rainforests and tropical forests are the lungs of the Earth, then surely wetlands function as its kidneys." Which one of the following functions of wetlands best reflects the above statement? (UPSC 2022)
A. The water cycle in wetlands involves surface runoff, subsoil percolation, and evaporation.
B. Algae form the nutrient base upon which fish, crustaceans, molluscs, birds, reptiles, and mammals thrive.
C. Wetlands play a vital role in maintaining sedimentation balance and soil stabilization.
D. Aquatic plants absorb heavy metals and excess nutrients.
Answer: D
3. If the tropical rainforest is removed, it does not regenerate quickly as compared to the tropical deciduous forest. This is because (UPSC 2011)
A. The soil of rain forest is deficient in nutrients.
B. propagules of the trees in the rainforest have poor viability.
C. The rainforest species are slow-growing.
D. exotic species invades the fertile soil of rain forest.
Answer: A
4. Consider the following States: 1. Arunachal Pradesh 2. Himachal Pradesh 3. Mizoram In which of the above States do 'Tropical Wet Evergreen Forests' occur? (UPSC 2015)
A. 1 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2 and 3
Answer: C
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Source: The Hindu
