Question 1 from UPSC CSE 2021 - Environment

Question

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.

Accepted Answer

Correct Option: C. 2, 3, and 4

Strategy: Focus on factors that actively inhibit tree growth rather than those that merely characterize the environment. Fire and grazing herbivores (statements 2 and 3) are well-known limiting factors, as they directly damage or remove tree saplings. Seasonal rainfall (statement 4) restricts tree water availability. Though burrowing animals and soil properties impact savannas, they do not primarily keep forest development in check, so omit those. Thus, select statements 2, 3, and 4.

Key Info: Savanna ecosystems are tropical or subtropical grasslands with scattered trees and shrubs. They are located between tropical rainforests and deserts, most notably in Africa (Serengeti), South America (Cerrado and Llanos), northern Australia, and parts of India. The open, park-like vegetation results from the interplay of several environmental and biological factors:

- Fire: Frequent natural and anthropogenic fires suppress the establishment or maturation of trees. Most savanna grasses are fire-adapted and regrow quickly, while younger trees often die from fire damage. Fire regimes determine tree density and landscape structure.

- Grazing herbivores: Large populations of grazing animals (such as zebras, antelopes, or buffalo) feed on seedlings and young shoots, preventing trees from establishing dominance. Combined with trampling, this controls woody plant encroachment.

- Seasonal rainfall: Savannas have distinct wet and dry seasons. Long periods of drought (dry season) restrict tree growth and favor grasses with deeper roots and faster life cycles. Rainfall is often insufficient or erratic, inhibiting the year-round water supply required by dense forests.

- Soil properties: Savanna soils tend to be shallow, low in nutrients, or have poor water retention. This can limit tree growth but is not typically the main agent suppressing forest development, rather it limits productivity overall.

- Burrowing animals and termites: These organisms modify soil properties and microhabitats, sometimes improving nutrient availability locally, but their net effect is not to suppress tree growth at the scale of the entire ecosystem.

Savanna management and balance are maintained through the cycle of fire, herbivory, and variable climate. These factors together selectively disadvantage trees while allowing grasses to dominate, thus keeping the region from progressing into a closed-canopy forest.

Answer

Option A: 1 and 2

Answer

Option B: 4 and 5

Answer

Option D: 1, 3, and 5