UPSC Prelims 2011 · GS Paper I

Question 23: Environment and Ecology

If a tropical rain forest is removed, it does not regenerate quickly as compared to a tropical deciduous forest. This is because

athe soil of rain forest is deficient in nutrients

bpropagules of the trees in a rain forest have poor viability

cthe rain forest species are slow-growing

dexotic species invade the fertile soil of rain forest

AnswerThe answer is (a).

In a tropical rain forest nearly all the nutrients are held in the living biomass and litter, not in the soil. Heavy rain leaches the soil and decomposition is fast, so the soil itself is nutrient-poor. When the forest is cleared, the nutrients leave with the vegetation and the soil cannot support quick regrowth. Soils under tropical deciduous forest hold more nutrients, so those forests recover faster. Remember: rain forest fertility sits in the trees, not the soil.

Why each option is right or wrong

(a) Right: the soil is nutrient-poor once the biomass is removed.
(b) Seed viability may play a part, but it is not the main reason.
(c) Growth rate is not the key reason; the poor soil is.
(d) Invasion by exotic species is not the main reason for slow regeneration.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2011, General Studies Paper I, Series A. The paper on upsc.gov.in.