Passage

Directions for the following 7 (seven) items : Read the following four passages and answer the items that follow. Your answers to these items should be based on the passages only. Passage—1 ‘Desertification’ is a term used to explain a process of decline in the biological productivity of an ecosystem, leading to total loss of productivity. While this phenomenon is often linked to the arid, semi-arid and sub-humid ecosystems, even in the humid tropics, the impact could be most dramatic. Impoverishment of human-impacted terrestrial ecosystems may exhibit itself in a variety of ways : accelerated erosion as in the mountain regions of the country, salinization of land as in the semi-arid and arid ‘green revolution’ areas of the country, e.g., Haryana and western Uttar Pradesh, and site quality decline—a common phenomenon due to general decline in tree cover and monotonous monoculture of rice/wheat across the Indian plains. A major consequence of deforestation is that it relates to adverse alterations in the hydrology and related soil and nutrient losses. The consequences of deforestation invariably arise out of site degradation through erosive losses. Tropical Asia, Africa and South America

With reference to 'desertification', as described in the passage, the following assumptions have been made : 1. Desertification is a phenomenon in tropical areas only. 2. Deforestation invariably leads to floods and desertification. Which of the above assumptions is/are valid?

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2 ✓ UPSC's answer

Why the answer is (d)

• The passage states that desertification is often linked to arid, semi-arid, and sub-humid ecosystems, but explicitly notes that its impact can be most dramatic in the humid tropics, meaning it is not limited to tropical areas only.

• Assumption 1 is invalid because the text describes desertification as a process of decline in biological productivity that occurs in various ecosystems, not exclusively in tropical regions.

• The passage states that the consequences of deforestation invariably arise out of site degradation through erosive losses, but it does not state that deforestation invariably leads to floods.

• Assumption 2 is invalid because while deforestation alters hydrology and causes soil loss, the text does not support the claim that it invariably causes floods.

• Since both assumptions are not supported by the specific details in the passage, neither is valid.

Why the other options are wrong

(a) 1 only: Assumption 1 is invalid because the passage states desertification occurs in arid, semi-arid, and sub-humid ecosystems as well, not just tropical areas.
(b) 2 only: Assumption 2 is invalid because the passage links deforestation to site degradation and erosive losses, but does not state it invariably leads to floods.
(c) Both 1 and 2: Both assumptions are invalid as the passage contradicts the exclusivity of tropical areas and the inevitable link to floods.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2018, held on 3 June 2018. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.