Practice question

Tropical forests commonly have very high net primary productivity per unit area because warm temperatures, abundant rainfall, and long growing seasons permit photosynthesis for much of the year. Their multilayered canopies intercept substantial light, and rapid nutrient uptake supports continuous leaf and wood production even where weathered soils contain small available nutrient pools. Open ocean has enormous total production globally because it covers such a vast area, but its productivity per square metre is generally low because nutrients are dilute or stratified away from surface light. Temperate forests have shorter growing seasons and cold-season constraints, while desert scrub is limited primarily by water. Coastal wetlands and coral reefs can match or exceed tropical forests locally, but they are not among the choices. NPP is the carbon retained after producers subtract their own respiration, so it measures new biomass available to food webs. The phrase “per unit area” is essential: it separates the intense year-round production of tropical forest from the large global contribution of spatially vast oceans.