Fishing and forestry

Fish are an important part of the human diet, accounting for a worldwide average 15% of humans' protein intake. Most of these fish are caught wild, and if fish are caught at a faster rate than the remaining fish can reproduce, the stock of fish will obviously decline. Trying to harvest more fish than the sea can produce is an example of unsustainability [unsustainability: an activity which uses up resources or damages the environment so that it cannot be continued in the future ].

Since the 1960s North Sea cod have been overfished, as more and more - and bigger - fishing boats caught more and more cod. At first, catches continued to increase each year. But then - surprise, surprise! - they started to decline, as there were not enough breeding fish left to maintain the cod population. Today, North Sea cod are in danger of extinction.

Forestry

Humans have now been cutting down trees for around 10,000 years - for wood to burn or build with, or to clear land for farming.

Forestry is sustainablesustainable: Sustainable means using something or doing something in a way that minimises damage to the environment and which avoids using up natural resources, eg by using renewable rather than scarce resources. as long as forests are allowed to replace themselves, or are replanted after harvesting - but often this is not done. The result is that the area of forest is steadily shrinking - a process called deforestationdeforestation: Deforestation is the destroying of forests by cutting down trees (for timber) or by burning. Often the purpose is to make way for agricultural land. - with profound consequences for ecosystems [ecosystems: communities of animals, plants and micro-organisms, together with the habitats where they live ] and biodiversity.

Deforestation:

• destroys forest habitats [habitats: Places inhabited by communities of living things. ], endangering many forest-dwelling species
• causes soil erosion, as the soil-stabilising effect of tree roots is removed. Barren land and flooding can result
• causes atmospheric pollution - mostly carbon dioxide - as forests are cleared by burning trees
• reduces the amount of photosynthesising vegetation, thus further increasing levels of carbon dioxide in the atmosphere

The maps give an idea of how much of the Earth's forest has been lost in the last 10,000 years.

The world's forests 8000 BC

The world's forests 2000CE

Particularly worrying is the rapid destruction of tropical rainforest [tropical rainforest: dense tropical equatorial woodland ]. This type of forest is often referred to as 'the Earth's lungs' because it produces around 40% of the world's atmospheric oxygen. It is also home to an estimated 50% of all species on Earth - once lost, the original habitats can never be replaced. Tropical rainforest is being cut down at the rate of 17 - 20 million hectares a year.