UPSC Prelims 2002 Q136: Environment & Ecology – Biogeochemical Cycles & Earth Systems
Consider the following ecosystems:
1. Taiga
2. Tropical evergreen
3. Tropical deciduous
4. Tundra
The correct sequence in decreasing order of the albedo values of these ecosystems is
- (a) 1, 4, 3, 2
- (b) 4, 1, 2, 3
- (c) 4, 1, 3, 2
- (d) 1, 4, 2, 3
Answer: (c) 4, 1, 3, 2
Explanation
Albedo of ecosystems in decreasing order
| Ecosystem | Albedo (reflectivity) |
|---|---|
| Tundra | Highest — snow-covered, about 0.6-0.8 in winter |
| Taiga | High — snow with dark conifers |
| Tropical deciduous | Moderate — about 0.15-0.2 |
| Tropical evergreen | Lowest — dense dark canopy, about 0.1-0.15 |
Albedo is highest where snow covers the ground, so tundra leads, followed by taiga (conifers with snow), tropical deciduous forest and finally dense tropical evergreen forest. The decreasing order is Tundra, Taiga, Tropical deciduous, Tropical evergreen, which is 4, 1, 3, 2.
Answer: (c) 4, 1, 3, 2.
Why each option is right or wrong
- (a) Incorrect. It puts the taiga above the tundra.
- (b) Incorrect. It puts the tropical evergreen forest above the deciduous forest.
- (c) CORRECT. Tundra, taiga, tropical deciduous, tropical evergreen.
- (d) Incorrect. It puts the taiga above the tundra and evergreen above deciduous.
Key point
Albedo: fresh snow 0.8-0.9, desert sand 0.3-0.4, grassland 0.2, forest 0.1-0.15, water 0.06.
Remember
Tundra > taiga > tropical deciduous > tropical evergreen.
Common mistakes
- Ranking the taiga above the tundra in albedo.
- Treating the tropical evergreen forest as brighter than the deciduous.
- Confusing albedo (reflection) with absorption of light.
Exam tip
Snow cover raises albedo; dense dark canopy lowers it.
Sources
- NCERT Class XII Biology — Ecosystem
- NCERT Class XI — Heat budget of the Earth