UPSC Prelims 2021 Q61: Savannah Vegetation Controls — Explained
The vegetation of savannah consists of grassland with scattered small trees, but extensive areas have no trees. The forest development in such areas is generally kept in check by one or more or a combination of some conditions. Which of the following are such conditions?
1. Burrowing animals and termites
2. Fire
3. Grazing herbivores
4. Seasonal rainfall
5. Soil properties
Select the correct answer using the code given below.
- 1 and 2
- 4 and 5
- 2, 3 and 4
- 1, 3 and 5
Answer: (c) 2, 3 and 4
Statement-wise explanation
- 1: incorrect — Termites and burrowing animals are typical savannah fauna. Termite mounds are a familiar sight in African and Australian savannahs. They mix and enrich the soil, but they do not suppress tree growth over large areas. Standard geography texts do not list them among the conditions that keep forest out of the savannah.
- 2: correct — Fires are frequent in the dry season, fuelled by tall grass that has dried out. They kill seedlings and young trees. Grasses survive because their growing points sit at or below the ground and they regrow after the rains. Only fire-tolerant trees with thick, corky bark survive, so tree cover stays scattered.
- 3: correct — Large herds of grazing and browsing animals, wild and domestic, eat and trample tree seedlings and saplings. This stops woody plants from growing into a closed canopy. Grazing and fire together are the classic disturbances that hold a savannah in its open state.
- 4: correct — Savannahs lie in the tropical wet and dry climate (Koeppen Aw). A rainy summer alternates with a long, hot dry season. Trees cannot get water year-round, while grasses complete their growth in the wet months and lie dormant in the dry ones. This seasonal water stress favours grass over forest.
- 5: incorrect — In the official key, soil properties are not one of the conditions that check forest growth. Ecologists do note that poor, leached lateritic soils can lower tree density in some places. However, the standard description of savannah, which this question follows closely, names seasonal rainfall, fire and grazing as the controls.
How to eliminate
Start with what is certain. Seasonal rainfall defines the savannah climate (wet summer, long dry winter), so statement 4 must be in the answer. That rules out the options with 1 and 2 only and with 1, 3 and 5. You are left with 4 and 5, or 2, 3 and 4. Fire and grazing are the two disturbances every geography text links to savannah grasslands. Dry-season grass fires and herds of herbivores are the textbook image of the biome. That points to 2, 3 and 4. The trap is statements 1 and 5: termites and soils sound scientific and are real parts of the savannah ecosystem, but they are not the standard 'controlling conditions'. Remember the triad: climate (seasonal rain) + fire + grazing.
Know more
Savannah: why grass wins over trees
Savannahs are tropical grasslands with scattered trees. They lie roughly between 5° and 20° latitude, on the poleward side of the equatorial rainforests, in the tropical wet and dry (Aw) climate. Rain falls mainly in the hot summer, when the sun is overhead and the ITCZ shifts towards the region. A long dry season follows.
Three forces keep these lands from turning into forest:
| Control | How it works |
|---|---|
| Seasonal rainfall | Months of drought stress trees; grasses grow fast in the rains and go dormant in the dry season |
| Fire | Dry grass burns easily; fires kill saplings, while grasses regrow from protected roots |
| Grazing / browsing | Herbivores eat and trample seedlings, keeping woody cover low |
Adaptations you should know
- Trees are often umbrella-shaped (e.g., acacia), with thick bark, deep roots and small or thorny leaves. Some, like the baobab, store water.
- Grasses are tall and coarse (elephant grass can exceed 3 m) and die back in the dry season.
Regional names
| Region | Name |
|---|---|
| East Africa | Savannah (Serengeti) |
| Venezuela, Colombia (Orinoco basin) | Llanos |
| Brazil (Brazilian Highlands) | Campos |
| Northern Australia | Downs / tropical savannah |
Contrast with temperate grasslands (Prairies, Steppes, Pampas, Veld, Downs). These are treeless mainly because of low rainfall and continental climate, not fire-grazing cycles in a monsoon-type climate.
India link: the Banni grassland (Kachchh) and the tall wet grasslands of Kaziranga are reminders that grasslands are natural ecosystems, not 'wastelands'.
NCERT Concepts to Revise
- Tropical wet and dry climate (Aw): Savannahs occur in the Aw climate; its rainfall pattern is what statement 4 asks about.
- Tropical grasslands of the world: Defines tropical grasslands as grass with scattered trees, the exact landscape the question describes.
- Tropical humid climates (A): Places the Aw savannah climate within the wider Koeppen group A tropical climates, helping you locate the biome.