Paper 1 · November 2022 · Soils
In Fig. 3.1's nutrient cycle for cleared rainforest, the arrow from biomass (B) to litter (L) is much smaller than in an undisturbed forest, and the soil (S) store shows a large outflow with only a thin inflow from weathering. What does this indicate about the cleared area's nutrient cycle compared with the undisturbed forest?
AThe soil store is being replenished by weathering input faster than it is depleted by leaching and erosion, so nutrient levels in the cleared area's soil are actually rising over time, unlike in the undisturbed forest.
BThe biomass store now holds most of the system's nutrients, exactly as it does in the undisturbed forest.
CLitter fall has increased because the remaining vegetation produces more leaf litter than the original forest canopy.
DThe cycle has been broken: the biomass store that held most nutrients is gone, and the soil store is being steadily depleted by leaching and erosion.
Explanation
Clearance removes most of the biomass store that normally holds the bulk of a rainforest's nutrients, and with reduced litter input and increased leaching and erosion, the soil store is depleted rather than replenished, breaking the tight, biomass-centred cycle of the undisturbed forest.
Derived from ZIMSEC Advanced Level Geography 6037/1 Paper 1: Physical Component, November 2022 session, Q3