Which one of the following ecosystems has maximum plant bio-mass?

The correct answer is B, Tropical rain forest. Standing crop biomass, the dry weight of living plant matter per unit area, is highest here because these forests are evergreen, get heavy rainfall and warmth all year, and have multi-layered canopies with very large trees.

• A) Tropical deciduous forest: Water is limited for several months, so trees shed leaves and growth stops for part of the year. Its standing crop is clearly lower than the rain forest.
• C) Temperate deciduous forest: Cold winters and a short growing season limit both growth and accumulated biomass. It is well below the tropical rain forest.
• D) Desert shrubs: Water scarcity keeps vegetation sparse and low. Biomass per square metre is among the lowest of all biomes.

The core concept is the difference between standing crop biomass and net primary productivity. Biomass is a stock. It accumulates where climate supports long growing seasons and tree longevity, which is why tropical rain forests hold the most. Productivity is a flow, and it is also high in these forests. This links to the Ecology unit and to Mains questions on carbon sequestration and the role of tropical forests in climate mitigation.

Trap: Students often pick the seasonal or deciduous option by thinking of rapid growth in the monsoon. Fast growth in a short season does not produce the largest biomass. Accumulated standing crop is what the question asks for.