ASRB NET: Environmental Science and Agroforestry

ASRB NET Environmental Science and Agroforestry covers ecology, environmental pollution, natural resource management and agroforestry systems. The exam tests ecosystem reasoning and quantitative estimates.

Core concepts

• Ecology: gross primary productivity minus respiration equals net primary productivity; only NPP is available to consumers.
• Pollution: air pollutants include SO2, NOx, ozone and particulate matter; water pollutants include BOD, nutrients and heavy metals; soil pollutants include pesticides and metals.
• Eutrophication follows nutrient enrichment, especially phosphorus in freshwater.
• Natural resource management uses the watershed approach, soil conservation and groundwater recharge.
• Agroforestry: tree–crop interactions can be competitive for light, water and nutrients or facilitative through shade, nitrogen fixation and soil organic matter.

Worked example

A 20 ha plantation has above-ground biomass of 50 t/ha with 50% carbon. Carbon stock = 20 × 50 × 0.5 = 500 t C. CO2 equivalent = 500 × 44/12 = 1,833 t CO2e. Reasoning: biomass is converted to carbon by the carbon fraction, then to CO2 using the molecular mass ratio. Below-ground biomass and soil carbon would add to the total.

Traps that cost marks

• Confusing GPP with NPP.
• Reporting total pollutant concentration as bioavailable or toxic fraction.
• Ignoring baseline carbon stocks when claiming sequestration.
• Assuming agroforestry always improves yield; competition can reduce crop yield.