IAS 2013 — Environment & Ecology Environment & Ecology

2013mcqmedium

In the grasslands, trees do not replace the grasses as a part of an ecological succession because of

Official previous-year question

Verified 2 Aug 2026.

Options

Ainsects and fungi
Blimited sunlight and paucity of nutrients
Cwater limits and fire
DNone of the above

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Solution

Correct Option

In grassland ecosystems, the ecological succession towards a forest community is primarily inhibited by two significant environmental factors that prevent the widespread establishment and dominance of trees over grasses:

Water Limits: Grasslands are typically found in regions with semi-arid climates or distinct dry seasons. The limited availability of soil moisture, particularly during critical growth periods, is often insufficient to support the higher water demands and extensive root systems required for the successful growth and survival of most tree species. This environmental constraint favors drought-tolerant grasses.
Fire: Frequent natural or human-induced fires are a characteristic feature of many grassland ecosystems. These fires regularly destroy tree saplings and young woody plants, which are generally more vulnerable to fire damage than grasses. Grasses, with their underground growing points, are adapted to recover quickly after a fire, thus maintaining their dominance and preventing the progression of succession to a tree-dominated stage.

Incorrect Options

Option 1 (insects and fungi): While insects and fungi can influence plant health and growth, they are not considered primary ecological factors that universally prevent tree establishment and succession in grasslands on a broad scale. Their impact is generally localized or secondary compared to climatic and disturbance regimes.
Option 2 (limited sunlight and paucity of nutrients): Sunlight is generally abundant in open grassland environments, not a limiting factor for tree growth. While nutrient availability can vary and may be limited in some grassland soils, it is not the primary or overarching reason preventing tree succession compared to water availability and fire regimes.
Option 4 (None of the above): This option is incorrect because option 3 accurately identifies the key ecological factors responsible for inhibiting tree succession in grasslands.

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Correct Option

Water Limits: Grasslands are typically found in regions with semi-arid climates or distinct dry seasons. The limited availability of soil moisture, particularly during critical growth periods, is often insufficient to support the higher water demands and extensive root systems required for the successful growth and survival of most tree species. This environmental constraint favors drought-tolerant grasses.
Fire: Frequent natural or human-induced fires are a characteristic feature of many grassland ecosystems. These fires regularly destroy tree saplings and young woody plants, which are generally more vulnerable to fire damage than grasses. Grasses, with their underground growing points, are adapted to recover quickly after a fire, thus maintaining their dominance and preventing the progression of succession to a tree-dominated stage.

Incorrect Options

Option 1 (insects and fungi): While insects and fungi can influence plant health and growth, they are not considered primary ecological factors that universally prevent tree establishment and succession in grasslands on a broad scale. Their impact is generally localized or secondary compared to climatic and disturbance regimes.
Option 2 (limited sunlight and paucity of nutrients): Sunlight is generally abundant in open grassland environments, not a limiting factor for tree growth. While nutrient availability can vary and may be limited in some grassland soils, it is not the primary or overarching reason preventing tree succession compared to water availability and fire regimes.
Option 4 (None of the above): This option is incorrect because option 3 accurately identifies the key ecological factors responsible for inhibiting tree succession in grasslands.