Previous Year Question
If a tropical rain forest is removed, it does not regenerate quickly as compared to a tropical deciduous forest. This is because
the soil of rain forest is deficient in nutrients
propagules of the trees in a rain forest have a poor viability
the rain forest species are slow-growing
exotic species invade the fertile soil of rain forest
Correct Answer: A
Detailed Solution
Most of the nutrients in a tropical rainforest are stored in the living biomass of plants and the organic material present near the surface rather than in the soil. Nutrients are rapidly cycled between vegetation and decomposing organic matter.
Heavy rainfall throughout the year causes intense chemical weathering and leaching of the soil. Soluble nutrients move into deeper soil layers or are washed away. Therefore, despite supporting dense vegetation, rainforest soils are generally highly weathered, acidic and deficient in nutrients.
When the forest is cleared, the plant biomass, leaf-litter layer and network of roots are destroyed. This breaks the rapid and nearly closed nutrient cycle of the forest.
After the vegetation cover is removed, the soil is directly exposed to heavy rainfall. Nutrient leaching and soil erosion increase, leaving insufficient nutrients for new plants. Consequently, the rainforest does not regenerate quickly.
In a tropical deciduous forest, the dry season and seasonal leaf fall result in less continuous leaching than in a rainforest, while fallen leaves add nutrients to the soil. Therefore, it can regenerate comparatively more quickly.
Option (b) is incorrect because the propagules of all rainforest trees do not inherently have poor viability. Option (c) is also not a general rule because many pioneer rainforest species grow rapidly. Option (d) is based on an incorrect premise because rainforest soil is generally nutrient-deficient rather than fertile. Hence, the correct answer is (a).