Ecosystems, Biomes and Environmental Change
What this domain tests
Ecosystems and biomes questions require you to explain how climate, soils and nutrient cycling produce distinctive global biomes, and how environmental change alters biodiversity and ecosystem services. Expect interpretation of climate graphs, nutrient-cycle diagrams and data on deforestation or conservation.
Core rules and concepts
- Gross primary production (GPP) is total photosynthesis; net primary production (NPP) = GPP − respiration by producers.
- Tropical rainforests have high NPP, rapid decomposition and tight nutrient cycling, but soils are often acidic and nutrient-poor because nutrients are stored in biomass.
- Taiga (boreal forest) has low temperatures, slow decomposition and acidic soils; temperate deciduous forest has seasonal leaf loss and richer litter.
- Biome distribution is controlled mainly by temperature and precipitation, with local variation from altitude, soils and drainage.
Worked example
A rainforest plot has GPP of 2,200 g C/m²/yr and plant respiration of 1,300 g C/m²/yr. NPP = 2,200 − 1,300 = 900 g C/m²/yr. This high NPP supports large biomass, but the litter layer is thin because decomposers work quickly in warm, wet conditions. The reasoning is to subtract respiration from GPP and then link the result to biomass and soil fertility, not assume high NPP means fertile soil.
Traps that cost marks
Do not equate high biodiversity with high soil fertility. Do not call all forest loss 'deforestation' without specifying cause and scale. In nutrient-cycle answers, avoid saying nutrients 'disappear'; they are stored, transferred or leached. Do not ignore the role of decomposers.