Sustainable harvesting and agricultureSpec D4.2.6, D4.2.7
In short
Harvesting a renewable resource from a natural ecosystem is sustainable only when the rate of harvesting is lower than the rate of replacement. This is assessed by monitoring populations, as with Brazil nut trees and Atlantic cod. The sustainability of agriculture depends on soil erosion, leaching of nutrients, supply of fertilizers, agrochemical pollution and carbon footprint.
Wild plants and fish are renewable resources. Sustainability depends on the rate of harvesting being lower than the rate of replacement by growth and reproduction.
| Example | How sustainability is assessed |
|---|---|
| Brazil nut tree (Bertholletia excelsa), harvested from wild Amazon forest | Surveys of the size and age structure of tree populations, repeated over years. A study of 23 populations (2003) found that stands with a long history of heavy nut collection lacked young trees, so recruitment may be too low to replace old trees. Later long-term studies at some sites found stable populations despite heavy collection, so sustainability must be assessed site by site. |
| Atlantic cod (Gadus morhua), marine fish | Stock assessments estimate the mass of breeding adults from catches and research surveys; a catch dominated by young fish is a sign of overfishing. Quotas and net mesh sizes are then set. The northern cod stock off Newfoundland collapsed and a moratorium on commercial fishing began in 1992. Canada reopened a commercial fishery in 2024, which is controversial because the stock is still well below its former size. |
Factors affecting the sustainability of agriculture
| Factor | Problem | More sustainable practice |
|---|---|---|
| Soil erosion | Bare, ploughed soil is washed or blown away | Cover crops, contour ploughing, hedgerows |
| Leaching of nutrients | Nitrate and phosphate dissolve and drain out of the soil | Apply fertilizer in smaller amounts when crops need it |
| Supply of fertilizers and other inputs | Phosphate is mined from finite rock deposits; nitrogen fertilizer manufacture uses large amounts of fossil fuel | Crop rotation with nitrogen-fixing legumes, use of manure |
| Pollution due to agrochemicals | Pesticides and herbicides harm non-target species and water | Integrated pest management, targeted spraying |
| Carbon footprint | CO₂ from machinery, transport and fertilizer manufacture; methane from livestock | Lower energy inputs, local supply chains |
Written and checked against the IB Biology SL specification · Updated October 2026