CDS (II) 2020 General Knowledge · Question 7 of 120

Correct — D, the tundra region. Tundra is defined by the absence of trees. It lies poleward of the tree line, where the growing season is only six to ten weeks, mean summer temperatures barely rise above 10 degrees Celsius, and a layer of permanently frozen subsoil stops roots from going deep and stops meltwater from draining. What grows there is mosses, lichens, sedges, cotton grass and dwarf shrubs such as prostrate willow and birch that hug the ground out of the wind. None of that yields timber. The other three regions all carry commercial timber: subtropical forests supply hardwoods, the temperate belt supplies both the deciduous hardwoods of the mid-latitudes and the great coniferous softwood belt, and the alpine zone of the Himalaya carries silver fir, juniper, pine and birch, which the NCERT text places between about 3,000 and 4,000 m.

• (a)Subtropical region — Subtropical forests are well wooded — sal, teak and other hardwoods in India, and pine on the lower Himalayan slopes. Timber is one of their main products.
• (b)Temperate region — The temperate belt is the world's principal source of timber, both the deciduous hardwoods of the mid-latitudes and the coniferous softwood forests that feed the pulp and construction trades.
• (c)Alpine region — The best of the wrong answers, because the highest alpine meadows really are treeless. But the alpine forest zone below them carries silver fir, juniper, pine and birch, so the region as a whole is not timberless.

Vegetation belts change with latitude and with altitude in the same order, from tropical forest through temperate forest to coniferous forest and finally to tundra or to alpine meadow. The boundary that matters for this question is the tree line, set by the length of the warm season rather than by cold alone: a tree needs enough consecutive warm weeks to make and harden new wood. Beyond that line, vegetation is low, slow-growing and shallow-rooted.

Two of the four options can be dismissed at once, since subtropical and temperate forests are where most of the world's timber comes from. The real decision is between alpine and tundra, and they are genuinely similar in appearance — both cold, both with a short season, both with a treeless upper zone. The separation is that alpine describes a zone on a mountain that begins below the tree line and continues above it, so it contains forest as well as meadow, while tundra names the belt that lies wholly beyond the tree line. Permafrost is the additional handicap in the tundra: even where a summer is warm enough, roots cannot penetrate the frozen subsoil.

• The tundra lies poleward of the tree line; its growing season is roughly six to ten weeks.
• Permanently frozen subsoil under the tundra blocks deep rooting and prevents drainage, so the surface is waterlogged in summer.
• Tundra vegetation is mosses, lichens, sedges, cotton grass and dwarf shrubs, none of which produces timber.
• NCERT places Himalayan alpine forest and pasture between about 3,000 and 4,000 m, with silver fir, juniper, pine, birch and rhododendron.
• Those alpine pastures are used for transhumance by the Gujjars, Bakarwals, Bhotiyas and Gaddis, who move herds up in summer and down in winter.

• Treating alpine and tundra as the same thing. Alpine names a mountain zone that includes forest; tundra names a belt entirely beyond the tree line.
• Assuming cold alone excludes trees. Very cold Siberian interiors carry dense coniferous forest because their summers, though short, are warm.
• Forgetting that permafrost, not just air temperature, is what keeps tundra treeless.

As a which-region-lacks-trees item, or as an altitudinal or latitudinal sequence question on vegetation belts.

• practice — not a real PYQ

  The absence of trees in the tundra is explained mainly by which one of the following?

  • (a)Excessive rainfall throughout the year
  • (b)A very short growing season together with permanently frozen subsoil
  • (c)Highly saline soils
  • (d)Continuous strong sunlight in summer

  Answer(b) A very short growing season together with permanently frozen subsoil — a tree needs enough consecutive warm weeks to make and harden new wood, and roots cannot penetrate permafrost.

• practice — not a real PYQ

  Silver fir, juniper, pine and birch are characteristic of which one of the following Himalayan zones?

  • (a)Tropical evergreen zone of the foothills
  • (b)Tropical deciduous zone
  • (c)Alpine zone between about 3,000 and 4,000 metres
  • (d)Mangrove zone

  Answer(c) Alpine zone between about 3,000 and 4,000 metres — above this the forest gives way to alpine pasture used for transhumance.