A biological resource is any living thing, or product of one, that humans use: timber, fish, crops, medicines, fibres, and ecosystem services such as soil fertility. Biological resources are renewable because they can regrow or reproduce, but they are only sustainable if they are used no faster than they are replaced.A resource is depleted when it is harvested faster than it can regenerate. As the human population and consumption per person rise, demand increases and many resources are over-exploited:
• forests are cleared for timber, farmland and settlements faster than they regrow;
• fish stocks fall when too many fish are caught for the population to recover;
• soil fertility and structure are lost through intensive farming and erosion;
• wild plants and animals are harvested for medicines, food and the pet trade.Sustainable use means meeting present needs without reducing the ability of future generations to meet theirs. It depends on harvesting at a rate equal to or below the rate of replacement.Worked example: in a woodland of 10 000 trees, 300 new trees reach harvestable size each year. Felling 300 trees a year is sustainable. Felling 500 a year reduces the stock by 200 trees per year, so it would be exhausted in 10 000 ÷ 200 = 50 years.Depletion also harms ecosystems: removing a species affects the food webs it belongs to, and loss of forest reduces a carbon sink. Farming and fishing are covered in detail in later lessons.
• forests are cleared for timber, farmland and settlements faster than they regrow;
• fish stocks fall when too many fish are caught for the population to recover;
• soil fertility and structure are lost through intensive farming and erosion;
• wild plants and animals are harvested for medicines, food and the pet trade.Sustainable use means meeting present needs without reducing the ability of future generations to meet theirs. It depends on harvesting at a rate equal to or below the rate of replacement.Worked example: in a woodland of 10 000 trees, 300 new trees reach harvestable size each year. Felling 300 trees a year is sustainable. Felling 500 a year reduces the stock by 200 trees per year, so it would be exhausted in 10 000 ÷ 200 = 50 years.Depletion also harms ecosystems: removing a species affects the food webs it belongs to, and loss of forest reduces a carbon sink. Farming and fishing are covered in detail in later lessons.