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Q63 (IAS/2023) Geography › World Physical Geography › Natural vegetation biomes Official Key

Consider the following statements : Statement-I : The soil in tropical rain forests is rich in nutrients. Statement-II : The high temperature and moisture of tropical rain forests cause dead organic matter in the soil to decompose quickly. Which one of the following is correct in respect of the above statements?

Result
Your answer: —  ·  Correct: D
Explanation

The correct answer is Option 4 because Statement-I is incorrect, while Statement-II is correct.

Contrary to common perception, the soil in tropical rainforests is nutrient-poor (oxisols/ultisols). While these regions support lush vegetation, the heavy and frequent rainfall leads to intense leaching, where essential soluble nutrients are washed away deep into the subsoil, leaving the topsoil acidic and deficient in minerals.

Statement-II accurately explains the underlying biological process. The high temperature and constant moisture create an ideal environment for decomposers (bacteria and fungi). Consequently, dead organic matter (leaf litter) decomposes extremely rapidly. Rather than being stored in the soil as humus, these nutrients are almost immediately reabsorbed by the dense root systems of the standing vegetation to support quick growth. Thus, the nutrients are locked in the biomass rather than the soil itself, making Statement-I false and Statement-II true.

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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Consider the following statements : Statement-I : The soil in tropical rain forests is rich in nutrients. Statement-II : The high tem…
At a glance
Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 6.7/10 · 3.3/10

This is a classic 'Conceptual Paradox' question found in every standard Geography NCERT. It tests the counter-intuitive fact that the world's lushest forests grow on some of the world's poorest soils. If you relied on 'common sense' (more trees = better soil), you walked into the trap.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Are soils in tropical rain forests rich in nutrients?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Explanation: > p. 429
Presence: 5/5
“• The tropical rain forests, if cleared, can yield productive farmland: this statement is wrong. The tropical soils are heavily leached. Some fertility is added by burning down the felled trees. This little fertility is lost after 2-3 crops. Can support intensive agriculture for several years even without chemical fertilizers: this is also wrong. Intensive agriculture for several years is not possible without adding fertilizers. So (d) A is false but R is true is the answer.”
Why this source?
  • Explicitly states tropical soils are heavily leached.
  • Says only a small, temporary fertility is added by burning and is lost after 2–3 crops, implying low inherent soil fertility.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 3: Terrestrial Ecosystems > 3.2.5. Tropical rain forests: > p. 25
Presence: 3/5
“• r Tropical rain forests occur near the equator. • r Tropical rain forests are among the most diverse and rich communities on the earth. • r Both temperature and humidity remain high and more or less uniform. • r The annual rainfall exceeds 300 cm and is generally distributed throughout the year. • The flora is highly diversified • The extreme dense vegetation of the tropical rain forests remains vertically stratified with tall trees often covered with vines, creepers, lianas, epiphytic orchids and bromeliads. • The lowest layer is an understory of trees, shrubs, herbs, like ferns and palms. • Soil of tropical rainforests are red latosols, and they are very thick”
Why this source?
  • Identifies rainforest soils as red latosols (lateritic soils) typical of tropical regions.
  • Specifies the characteristic soil type (red latosols), supporting inference about distinctive tropical soil properties relevant to nutrient status.
Statement 2
Do high temperature and high moisture in tropical rain forests cause dead organic matter in the soil to decompose quickly?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 5
Presence: 5/5
“In the equatorial evergreen rainforest biome, as many as 3000 species may be found in a few square kilometres. Te ground surface is generally covered only by a thin litter of leaves. Dead plant matter (leaves, etc.) rapidly decomposes, because the warm temperatures and abundant moisture promote its breakdown by bacteria. Nutrients released by decay are quickly absorbed by roots. As a result, the soil is low in organic matter (humus). Many species of plants and animals in this very diverse ecosystem still have not been identifed or named by ecologists. In the equatorial rainforest, because of the competition for light, ecological niches are distributed vertically rather than horizontally.”
Why this source?
  • Directly links warm temperatures and abundant moisture to rapid bacterial breakdown of dead plant matter.
  • Explains rapid nutrient release and immediate root uptake, producing soils low in organic matter (humus).
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Presence: 5/5
“The vegetative cover and organisms that occupy the parent materials from the beginning and also at later stages help in adding organic matter, moisture retention, nitrogen etc. Dead plants provide humus, the finely divided organic matter of the soil. Some organic acids which form during humification aid in decomposing the minerals of the soil parent materials. Intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus accumulates in cold climates as bacterial growth is slow. With undecomposed organic matter because of low bacterial activity, layers of peat develop in subarctic and tundra climates. In humid tropical and equatorial climates, bacterial growth and action is intense and dead vegetation is rapidly oxidised leaving very low humus content in the soil.”
Why this source?
  • States bacterial growth is intense in humid tropical/equatorial climates, accelerating decomposition.
  • Specifies dead vegetation is rapidly oxidized in these climates, leaving very low humus content.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Equatorial Vegetation > p. 426
Presence: 3/5
“• High temperature and abundant rainfall support a luxuriant tropical rainforest. In the Amazon lowlands, the forest is so dense that it is called selvas. From the air, the tropical rain forest appears like a thick canopy of foliage, broken only where it is crossed by large rivers or cleared for cultivation.• Selvas are dense tropical rainforests usually having a dense canopy (cloud cover).• The growing season is all year round (seeding, flowering, and decay do not take place in a seasonal pattern). The tallest trees attain a height close to 50 m. The smaller trees beneath form the next layer.• Because the tall trees cut out most of the sunlight, the undergrowth is not dense with shade-tolerant ferns and herbaceous plants.”
Why this source?
  • Notes a year‑round growing season in equatorial regions, so decay occurs continuously rather than seasonally.
  • Links high temperature and abundant rainfall to luxuriant forests where continuous turnover (growth + decay) is possible.
Statement 3
Does the rapid decomposition of dead organic matter caused by high temperature and moisture explain why tropical rain forest soils are rich in nutrients?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes. Warm and moist environment favours decomposition whereas low temperature"
Why this source?
  • Explicitly identifies temperature and soil moisture as the most important climatic factors regulating decomposition.
  • States that a warm and moist environment favours decomposition, linking high temperature/moisture to faster breakdown of organic matter.
Web source
Presence: 4/5
"They meet their energy and nutrient requirements by degrading dead organic matter or detritus. These are also known as saprotrophs (sapro: to decompose). Decomposers secrete digestive enzymes that breakdown dead and waste materials (such as faeces) into simple absorbable substances."
Why this source?
  • Describes decomposers as organisms that degrade dead organic matter (detritus).
  • Says decomposers break down dead and waste materials into simple absorbable substances, connecting decomposition to nutrient release.
Web source
Presence: 3/5
"Simultaneous increase or decrease of temperature and moisture beyond the optimal levels brought about a decline in the rate of organic matter decomposition."
Why this source?
  • Notes that changes in temperature and moisture affect decomposition rates, indicating a direct climate–decomposition link.
  • Provides a nuance that deviations beyond optimal temperature/moisture can reduce decomposition, qualifying the simple high-temperature/high-moisture explanation.

Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 5
Strength: 5/5
“In the equatorial evergreen rainforest biome, as many as 3000 species may be found in a few square kilometres. Te ground surface is generally covered only by a thin litter of leaves. Dead plant matter (leaves, etc.) rapidly decomposes, because the warm temperatures and abundant moisture promote its breakdown by bacteria. Nutrients released by decay are quickly absorbed by roots. As a result, the soil is low in organic matter (humus). Many species of plants and animals in this very diverse ecosystem still have not been identifed or named by ecologists. In the equatorial rainforest, because of the competition for light, ecological niches are distributed vertically rather than horizontally.”
Why relevant

States that warm temperatures and abundant moisture cause dead plant matter to rapidly decompose and that nutrients released by decay are quickly absorbed by roots, leaving the soil low in organic matter (humus).

How to extend

A student could combine this with the basic fact that tropical zones are warm and wet to infer decomposition is rapid there and then ask whether rapid uptake by plants leaves little nutrient storage in the soil.

FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Strength: 5/5
“The vegetative cover and organisms that occupy the parent materials from the beginning and also at later stages help in adding organic matter, moisture retention, nitrogen etc. Dead plants provide humus, the finely divided organic matter of the soil. Some organic acids which form during humification aid in decomposing the minerals of the soil parent materials. Intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus accumulates in cold climates as bacterial growth is slow. With undecomposed organic matter because of low bacterial activity, layers of peat develop in subarctic and tundra climates. In humid tropical and equatorial climates, bacterial growth and action is intense and dead vegetation is rapidly oxidised leaving very low humus content in the soil.”
Why relevant

Explains a general rule: in humid tropical climates bacterial growth is intense and dead vegetation is rapidly oxidised, so humus accumulates in cold climates but not in warm ones.

How to extend

Using the rule plus knowledge that tropics are warm/wet, a student could predict low humus and then test whether that implies soils are nutrient-poor or nutrient-rich at different timescales.

Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Explanation: > p. 428
Strength: 5/5
“• The fertility of topsoil in rainforest regions is very poor. Torrential downpours leach out most of the topsoil nutrients.• Leaching: percolation and draining way of nutrients due to rainwater action.• The soil deteriorates rapidly with subsequent soil erosion and soil impoverishment. It takes decades to replenish the soil of lost nutrients. Thus, a seed doesn't usually germinate, and even if it does, its development is hindered due to little availability of sunlight. Lalang (tall grass) and thick undergrowth spring up as soon as the trees are cut. They choke the restoration of forests.• The Indonesian Island of Java is an exception because of its rich volcanic ashes.”
Why relevant

Gives a process (leaching by torrential downpours) and states fertility of topsoil in rainforest regions is very poor, linking heavy rainfall to nutrient loss.

How to extend

A student could combine heavy-rain leaching with rapid decomposition (nutrients released but then leached) to evaluate whether net soil nutrient levels are high or low.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 15: The Hot, Wet Equatorial Climate > Sample Objective Ouestions > p. 156
Strength: 4/5
“The undergrowth in the equatorial rain forest is sparse because • A the tropical laterite soil is too infertile • B sunlight cannot reach the ground of the dense forests • C wild animals and insect pests devour much of the undergrowth • D ground temperature is low”
Why relevant

An objective question option identifies tropical laterite soil as 'too infertile' as a reason for sparse undergrowth, suggesting a pattern of low soil fertility in equatorial forests.

How to extend

A student could use this as an example that despite dense vegetation, soil infertility is common in equatorial climates and investigate mechanisms (decomposition + leaching) that explain it.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 3: Terrestrial Ecosystems > 3.2.5. Tropical rain forests: > p. 25
Strength: 4/5
“• r Tropical rain forests occur near the equator. • r Tropical rain forests are among the most diverse and rich communities on the earth. • r Both temperature and humidity remain high and more or less uniform. • r The annual rainfall exceeds 300 cm and is generally distributed throughout the year. • The flora is highly diversified • The extreme dense vegetation of the tropical rain forests remains vertically stratified with tall trees often covered with vines, creepers, lianas, epiphytic orchids and bromeliads. • The lowest layer is an understory of trees, shrubs, herbs, like ferns and palms. • Soil of tropical rainforests are red latosols, and they are very thick”
Why relevant

Describes tropical rain forests as occurring near the equator with high and uniform temperature and humidity and notes soils are red latosols (a characteristic tropical soil).

How to extend

Using the climate description plus knowledge that latosols are often heavily weathered, a student could link climate-driven decomposition/weathering to likely low retained soil nutrients.

Pattern takeaway: UPSC loves testing 'Ecological Paradoxes'—situations where the visual outcome (lush forest) contradicts the underlying mechanism (poor soil). They want to see if you understand the *process* (leaching + rapid uptake) rather than just the *picture*.
How you should have studied
  1. [THE VERDICT]: Sitter. Directly lifted from NCERT Class XI (Fundamentals of Physical Geography, Ch: Geomorphic Processes/Soils) and Majid Hussain (Biomes).
  2. [THE CONCEPTUAL TRIGGER]: The 'Nutrient Cycling' theme in Biogeography. Specifically, the relationship between Temperature, Moisture, and Bacterial Activity.
  3. [THE HORIZONTAL EXPANSION]: Contrast this with other biomes: Tundra (Low temp = Slow decomp = Peat accumulation); Grasslands (Moderate rain = High humus = Chernozems/Black Soil); Coniferous (Acidic needles = Podzolization). Memorize the soil types: Oxisols/Laterites (Tropics) vs. Spodosols (Taiga).
  4. [THE STRATEGIC METACOGNITION]: Do not study biomes as static lists of trees. Study them as 'Chemical Reactors'. Ask: Where are the nutrients stored? In Rainforests, the bank is the Biomass (trees); in Grasslands, the bank is the Soil.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 Lateritic (latosol) soils in the humid tropics
💡 The insight

Tropical rain forests commonly develop red latosols (lateritic soils), which are the dominant soil type under these forests.

High-yield: explains why tropical vegetation is dense yet soils can be poor; links soil type to questions on land use, agriculture and forest conversion. Mastery helps answer questions about soil classification, fertility and sustainable farming in tropical regions.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 3: Terrestrial Ecosystems > 3.2.5. Tropical rain forests: > p. 25
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Explanation: > p. 429
🔗 Anchor: "Are soils in tropical rain forests rich in nutrients?"
📌 Adjacent topic to master
S1
👉 Leaching and loss of soil fertility
💡 The insight

Heavy leaching in humid tropical climates removes soluble nutrients, producing soils with low inherent fertility and only short-lived gains after burning vegetation.

Crucial for questions on shifting cultivation, sustainability, and why cleared rain forest land fails after a few crops; connects climate (high rainfall) to pedogenesis and agricultural outcomes.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Explanation: > p. 429
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 1: Ecology > r.3.6. Biosphere > p. 10
🔗 Anchor: "Are soils in tropical rain forests rich in nutrients?"
📌 Adjacent topic to master
S1
👉 High aboveground productivity despite poor soils
💡 The insight

Tropical rain forests are extremely diverse and productive aboveground while the soils remain heavily leached and of low fertility.

Useful for explaining the apparent paradox in ecology and geography papers: why biomass and biodiversity can be high even when soil nutrients are low; links to nutrient cycling and ecosystem services questions.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 3: Terrestrial Ecosystems > 3.2.5. Tropical rain forests: > p. 25
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Explanation: > p. 429
🔗 Anchor: "Are soils in tropical rain forests rich in nutrients?"
📌 Adjacent topic to master
S2
👉 Temperature and moisture control microbial decomposition rates
💡 The insight

High temperature combined with abundant moisture accelerates bacterial growth and the breakdown of dead plant material in tropical rainforests.

High-yield concept for questions on nutrient cycling, soil fertility and biome functioning; connects microbiology of decomposition with land‑use outcomes (e.g., short-lived fertility after forest clearing). Mastering this helps answer comparative questions on soils across climates and on post-deforestation agriculture.

📚 Reading List :
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 5
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Decomposers or Saprophytes > p. 31
🔗 Anchor: "Do high temperature and high moisture in tropical rain forests cause dead organi..."
📌 Adjacent topic to master
S2
👉 Low humus and nutrient-poor soils in rainforests
💡 The insight

Rapid decomposition and immediate root uptake prevent accumulation of organic matter, leaving rainforest soils low in humus despite high productivity.

Essential for explaining why tropical forests often produce poor soils for sustained agriculture, for linking vegetation productivity with soil profiles (laterites), and for answering questions about conservation and land management after deforestation.

📚 Reading List :
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 5
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
🔗 Anchor: "Do high temperature and high moisture in tropical rain forests cause dead organi..."
📌 Adjacent topic to master
S2
👉 Year‑round growth implies continuous decomposition
💡 The insight

Equatorial climates lack a dormant season, so decay processes operate continuously rather than seasonally, increasing turnover of organic matter.

Useful for comparing biomes (tropical vs temperate/tundra), understanding peat formation absence in tropics, and tackling questions on seasonal vs perennial ecosystem processes.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Equatorial Vegetation > p. 426
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 5
🔗 Anchor: "Do high temperature and high moisture in tropical rain forests cause dead organi..."
📌 Adjacent topic to master
S3
👉 Decomposition rate and humus accumulation
💡 The insight

High temperature and moisture accelerate microbial decomposition, resulting in low humus accumulation in tropical soils.

Explaining contrasts in soil organic matter across climates is high-yield for geography and environment questions; it links microbial activity to soil fertility and helps answer questions on biome-specific soil properties and land-use implications.

📚 Reading List :
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 5
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
🔗 Anchor: "Does the rapid decomposition of dead organic matter caused by high temperature a..."
🌑 The Hidden Trap

Since they asked about rapid decomposition in Tropics, the next logical question is the exact opposite: 'Peat Formation' in Tundra/Boreal regions. Because of low temperatures, bacterial activity is inhibited, leading to massive carbon storage in soil (Peat) rather than biomass. Also, look out for 'Blue Carbon' (Mangroves/Seagrass) which stores carbon in anaerobic soil conditions.

⚡ Elimination Cheat Code

Use the 'Stock vs. Flow' Logic. If Statement II is true (decomposition is fast due to heat/moisture), then nutrients are being released and used up rapidly (High Flow). If the flow is super fast, the stock (Statement I: Soil richness) cannot be high. The two statements are functionally contradictory. Since high heat/moisture undeniably speeds up chemical reactions (Science 101), Statement II is the anchor truth, making Statement I false.

🔗 Mains Connection

Mains GS-3 (Agriculture & Environment): This concept explains why 'Shifting Cultivation' (Jhum) fails if the fallow period is too short. Once the vegetation (the nutrient bank) is burnt and crops are grown, the soil (which is inherently poor) loses fertility within 2-3 cycles. This is the scientific basis for arguing against slash-and-burn in high-density populations.

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SIMILAR QUESTIONS

NDA-II · 2016 · Q3 Relevance score: 2.59

Statement I : The laterite soils develop in areas with high temperature and high rainfall. Statement I : Laterite soils are the result of intense leaching process.

IAS · 2024 · Q7 Relevance score: 2.51

Consider the following statements : Statement-I : Rainfall is one of the reasons for weathering of rocks. Statement-II : Rain water contains carbon dioxide in solution. Statement-III : Rain water contains atmospheric oxygen. Which one of the following is correct in respect of the above statements ?

CAPF · 2013 · Q122 Relevance score: 2.07

Statement I : Virgin soils of newly cleared forests give higher yield of coffee. Statement I : Coffee is a soil nutrient exhaustive crop.

IAS · 2025 · Q26 Relevance score: 1.78

Consider the following statements : Statement I : The amount of dust particles in the atmosphere is more in subtropical and temperate areas than in equatorial and polar regions. Statement II : Subtropical and temperate areas have less dry winds. Which one of the following is correct in respect of the above statements?