Geomorphic factors influencing plant and animal distributions are
- (a)slope angle and relief only
- (b)slope aspect and relative relief
- (c)slope angle, slope aspect and relief
- (d)slope angle, slope aspect and relative relief
Correct — C, slope angle, slope aspect and relief. Biogeography separates the controls on where plants and animals live into climatic, edaphic, biotic and geomorphic groups, and the geomorphic set is the landform set: how steep the ground is, which way it faces, and how much height difference the terrain carries. Slope angle governs how fast water drains and how much soil can stay put — a steep face sheds both, so it supports thin-soiled, drought-tolerant communities while the gentler footslope collects them. Slope aspect decides how much sun a face receives: in the northern hemisphere a south-facing slope is warmer and drier and a north-facing one cooler and moister, and in the Himalaya the two sides of the same ridge often carry visibly different forest. Relief — the height range of the land — creates the altitudinal belts that let temperate species live at low latitudes and puts an alpine zone above a tropical forest on the same mountain. Those three together are what option (c) lists.
- (a)slope angle and relief only — Drops slope aspect, which is the one geomorphic control that can flip a habitat without any change in height or steepness. The word 'only' makes the omission fatal.
- (b)slope aspect and relative relief — Leaves out slope angle altogether, and slope angle is the primary control on drainage and soil depth. A two-item list cannot be the answer when three of the four listed controls are real.
- (d)slope angle, slope aspect and relative relief — The near-miss, and the reason this item is worth slowing down for. It substitutes relative relief — the height difference between the highest and lowest points of one small area — for relief in the general sense. Relative relief is a narrower, measured index used in terrain analysis; the biogeographic control is overall relief, which the key takes as the third factor.
Geomorphic (or landform) factors are one of the standard groups of ecological controls, alongside climatic, edaphic and biotic factors. The three usually listed are slope steepness, slope aspect and relief. They act indirectly: none of them feeds a plant, but each redistributes the things that do — sunlight, water, soil and temperature — across a landscape that has the same regional climate throughout.
The whole item turns on the difference between two of its own words. Options (c) and (d) name the same first two factors and part company only on 'relief' versus 'relative relief'. Relative relief is a specific quantity — the difference between the highest and lowest elevation within a defined unit area — and it belongs to terrain morphometry rather than to the standard list of biogeographic controls. If your own reading favours (d), the key does not, and (c) is what has to be authored: the standard triad is slope angle, slope aspect and relief. A worked example makes the third factor concrete: on a single Himalayan spur the aspect changes the forest between two sides of the ridge, and the relief stacks subtropical, temperate and alpine belts one above the other.
- Ecological controls are usually grouped as climatic, edaphic, biotic and geomorphic; the geomorphic group is slope angle, slope aspect and relief.
- Slope angle controls runoff, drainage and how deep a soil can develop before gravity moves it.
- In the northern hemisphere, south-facing slopes receive more insolation and are warmer and drier than north-facing ones at the same altitude.
- Relief produces altitudinal zonation, which is why tropical highlands stack several climate and vegetation belts on one mountain.
- Relative relief is a measured index — highest minus lowest elevation in a unit area — and is not the same thing as relief in general.
Options (c) and (d) differ by one word; the key takes relief, not relative relief.
- Treating relief and relative relief as interchangeable; the second is a measured index over a defined area.
- Ignoring aspect because it is invisible on a contour map — it is often the strongest local control on vegetation.
- Assuming all controls are climatic; two sites under the same regional climate can carry different communities purely on landform.
As a 'which factors belong to this group' item, or through an application — why two sides of a ridge carry different forest, or why tropical highlands show vertical zonation.
Consider the following statements: 1. In equatorial regions, the year is divided into four main seasons 2. In Mediterranean region, summer receives more rain 3. In China type climate, rainfall occurs throughout the year 4. Tropical highlands exhibit vertical zonation of different climates Which of these statements are correct?
- (a) 1, 2, 3 and 4
- (b) 1, 2 and 3
- (c) 1, 2 and 4
- (d) 3 and 4
Answer(d) 3 and 4
Statement 4 of that UPSC item is the relief factor in action. Vertical zonation in tropical highlands is precisely what relief does to climate and, through it, to plant and animal distribution — the third of the three geomorphic controls this CDS question asks you to name.
- practice — not a real PYQ
In the northern hemisphere, a south-facing slope generally differs from a north-facing slope at the same altitude by being
- (a)warmer and drier
- (b)cooler and moister
- (c)steeper
- (d)richer in organic matter
Answer(a) warmer and drier — it receives more direct insolation, so evaporation is higher and the vegetation is usually more drought-tolerant.
- practice — not a real PYQ
The stacking of tropical, temperate and alpine vegetation belts on a single mountain is chiefly a consequence of
- (a)slope aspect
- (b)relief
- (c)soil texture
- (d)latitude
Answer(b) relief — the height range of the land produces altitudinal zonation, so climate and vegetation change with elevation on one slope.