NCERT Solutions for Class 9th Science Chapter 12 Forests as barriers against disasters — Bridging Science and Society

Book page 244 Updated on2026-09-08

Q1.
How do forests with rich and highly diverse flora and fauna work as a barrier and reduce the impact of disasters?
Answer

A biodiverse forest acts as three barriers at once — physical, biological and chemical. The chapter gives one worked example of each.

Type of barrierExample from the chapterMechanism
PhysicalThe 1999 super cyclone in Orissa: villages with more mangroves experienced less destructionDense mangrove roots and trunks break the force of wind and storm surge, and hold the sediment so the shoreline is not stripped away
BiologicalMonkey Fever (Kyasanur Forest Disease, KFD) in the Western Ghats: rich biodiversity correlates with lower tick-borne disease riskMany of the animals a tick feeds on are hosts in which the virus cannot replicate. The more such species there are, the more tick bites are "wasted" on dead-end hosts, so fewer infected ticks reach people
ChemicalForest soils and plant roots; mangrove soilsDiverse microorganisms absorb, transform or break down pollutants, improving water quality; mangrove soils trap sediments and heavy metals, preventing pollution from spreading into oceans and rivers
Why diversity and not just tree cover: in each case the protection comes from having many different kinds of organism doing overlapping jobs. A single-species plantation gives some wind break, but it has one root architecture, one set of soil microbes and one set of animal hosts. If a pest or a disease or a salt surge takes out that one species, the whole barrier fails at once. A diverse forest keeps working because when one species fails, others are still doing the job. That property has a name worth knowing: ecological redundancy, and it is what makes a diverse system stable.
Connect it forward: this is also the reason section 12.10 treats biodiversity loss as urgent. Losing species does not only reduce the number of names on a list — it thins out the barrier, and the damage shows up only when the next cyclone or outbreak arrives.
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