UPPSC 2025 Prelims GS Paper-I · Question 103 of 150

Correct — D, both (A) and (R) are true and (R) is the correct explanation of (A). The Assertion is true: no other Indian region packs so many vegetation types into so small a horizontal distance. Walking up from the Terai you pass tropical moist deciduous sal forest, then subtropical chir pine, then temperate oak, deodar, fir and spruce, then sub-alpine birch and rhododendron, then alpine meadows, and finally bare rock and permanent snow. The Reason is also true: air temperature falls with height at roughly 6.5 degrees Celsius for every 1,000 metres, so climate changes continuously up a Himalayan slope. And the Reason is precisely why the Assertion holds. Vegetation is controlled above everything else by temperature and moisture, so where climate changes with altitude the plant community must change with it — a climb of three or four thousand metres reproduces the temperature gradient that would otherwise require a journey of thousands of kilometres towards the pole. That is altitudinal zonation, a causal link and not a coincidence, so the answer is not merely 'both true' but 'both true AND R explains A'.

• (a)Both (A) and (R) are true, but (R) is not the correct explanation of (A) — This is the real trap of the question, and it catches two kinds of candidate: the one who assumes by reflex that two true statements must be unconnected, and the one who reads the code in its usual UPSC order and thinks option (a) is the 'R explains A' choice. Both statements are true, but the altitudinal change in climate is not an incidental fact standing beside the variety of vegetation — it is the mechanism that produces it. Remove the temperature and moisture gradient and there is no reason for the vegetation to change at all.
• (b)(A) is true, but (R) is false — The Reason is a plain fact of physical geography. In the troposphere temperature falls with height at the normal lapse rate of about 6.5 degrees Celsius per kilometre, and Himalayan slopes also show sharp changes in precipitation, humidity and length of the growing season with height. There is nothing false in R.
• (c)(A) is false, but (R) is true — The Assertion is not false. Champion and Seth's Revised Survey of the Forest Types of India recognises several forest type groups that occur only in the Himalaya — Himalayan moist temperate, Himalayan dry temperate, sub-alpine, moist alpine scrub and dry alpine scrub — on top of the tropical and subtropical types found at the foot of the range. The diversity of Himalayan vegetation is exactly what the classification records.

Altitudinal zonation is the arrangement of plant communities in horizontal belts up a mountainside, produced because temperature falls and moisture, wind exposure and growing-season length change with height. In the Himalaya the sequence from the foothills upward is broadly: tropical moist deciduous sal forest in the Bhabar, Terai and Shivalik; subtropical pine forest dominated by chir pine at roughly 1,000 to 2,000 metres; Himalayan moist and dry temperate forest of oak, deodar, blue pine, silver fir and spruce from about 1,500 to 3,000 metres; sub-alpine birch, juniper and rhododendron up to the tree line; alpine meadows above it; and finally lichens, mosses and permanent snow. Altitude is the leading control, but rainfall and slope aspect matter too, which is why the wetter eastern Himalaya carries evergreen forest at heights where the drier western Himalaya carries chir pine and deodar.

Handle any assertion-reason item in three steps: is A true on its own, is R true on its own, and only then does R actually cause or account for A. Here both halves are safely true, so the whole decision is between 'both true, unrelated' and 'both true, R explains A'. The test for a correct explanation is whether removing R would leave A unsupported, and it plainly would: take away the change of climate with height and there is nothing left to make the vegetation change. Read the option text before you mark, though — this 2025 booklet lists the codes in a non-standard order, with (a) as 'both true but R is not the explanation' and (d) as 'both true and R is the correct explanation'. A candidate who marks by habit rather than by reading will put down (a) and lose the mark.

• Temperature in the lower atmosphere falls with height at the normal lapse rate of about 6.5 degrees Celsius per 1,000 metres, so a Himalayan slope compresses into a few kilometres of climb the climatic range of a journey of thousands of kilometres in latitude
• The Himalayan vegetation sequence runs tropical moist deciduous sal, subtropical chir pine, temperate oak-deodar-fir-spruce, sub-alpine birch and rhododendron, alpine meadow, and finally permanent snow
• The tree line in the Indian Himalaya generally lies around 3,500 to 4,000 metres; the alpine meadows above it are called bugyals in Uttarakhand and margs in Kashmir
• Champion and Seth's Revised Survey of the Forest Types of India (1968) recognises 16 major forest type groups for the country, and several of them — Himalayan moist temperate, Himalayan dry temperate, sub-alpine, moist alpine scrub and dry alpine scrub — are confined to the Himalaya
• Rainfall and aspect modify the pattern: the heavily watered eastern Himalaya supports evergreen forest at elevations where the drier western Himalaya carries chir pine and deodar

• In this 2025 booklet the assertion-reason codes are printed in a non-standard order: (a) is 'both true, R is NOT the explanation' and (d) is 'both true, R IS the explanation'. Marking from memory of the usual UPSC order costs the mark even when the reasoning is right
• Treating two true statements as automatically unrelated; here the climate gradient is the mechanism behind the vegetation variety, not a fact standing beside it
• Attributing Himalayan vegetation variety to soil or to latitude; within the range it is altitude, and secondarily rainfall and aspect, that does the work

UPPSC likes this topic as an assertion-reason pair or as a species-to-belt match list, because it can be answered from NCERT physical geography without any current data; UPSC asks it obliquely instead — which plants grow naturally in the Himalaya, which national park lies wholly in the alpine zone, or which forest type a named species dominates.

• practice — not a real PYQ

  The alpine meadows lying above the tree line in the Uttarakhand Himalaya are locally known as

  • (a)Bugyal
  • (b)Bhabar
  • (c)Duar
  • (d)Terai

  Answer(a) Bugyal — the high-altitude grasslands above the tree line in Uttarakhand; Bhabar and Terai are belts at the foot of the mountains and the Duars are the plains of north Bengal and Assam.

• practice — not a real PYQ

  Chir pine (Pinus roxburghii) is the characteristic tree of which vegetation belt of the Himalaya?

  • (a)The tropical moist deciduous belt of the Terai
  • (b)The subtropical belt at roughly 1,000 to 2,000 metres
  • (c)The sub-alpine belt just below the tree line
  • (d)The alpine meadow belt above the tree line

  Answer(b) The subtropical belt at roughly 1,000 to 2,000 metres — chir pine forms the Himalayan subtropical pine forests; sal holds the Terai belt, birch and rhododendron the sub-alpine belt, and grasses and herbs the alpine meadows.