RAS question
Arrange the following biomes in INCREASING order of their annual net primary productivity (NPP) per unit area (lowest to highest):
Correct answer: (C) Tundra < Temperate Grassland < Taiga < Tropical Rainforest.
For these biomes, annual net primary productivity per unit area rises in the order Tundra < Temperate Grassland < Taiga < Tropical Rainforest.
Explanation
Net primary productivity per unit area is lowest where the growing season is shortest and highest where warmth and moisture support year-round biomass production. Portland State University lists tundra and alpine at 140 g m^-2 y^-1, temperate grassland at 600 g m^-2 y^-1, boreal forest/Taiga at 800 g m^-2 y^-1, and tropical rainforest at 2200 g m^-2 y^-1. The increasing sequence is Tundra < Temperate Grassland < Taiga < Tropical Rainforest. Grassland is not automatically more productive than taiga; taiga is higher per unit area than temperate grassland, while tropical rainforest remains the clear maximum.
Why the other options are wrong
- (A) It reverses the middle pair: boreal forest/Taiga has 800 g m^-2 y^-1 and temperate grassland has 600 g m^-2 y^-1, so temperate grassland should come before taiga.
- (B) It starts with taiga below tundra, but tundra and alpine have 140 g m^-2 y^-1 and boreal forest/Taiga has 800 g m^-2 y^-1.
- (D) It places temperate grassland below tundra, whereas temperate grassland has 600 g m^-2 y^-1 against tundra and alpine at 140 g m^-2 y^-1.
Concept
World Geography and ecology rank biomes by net primary productivity per unit area. RAS-style ecology comparisons often link biome climate limits, growing season, and biomass production in a compact sequence.