Hosta

English: Understanding and seeing the drivers of forest loss

‘Forest loss’ or ‘tree loss’ captures two fundamental impacts on forest cover: deforestation and forest degradation.

Deforestation is the complete removal of trees for the conversion of forest to another land use such as agriculture, mining, or towns and cities. It results in a permanent conversion of forest into an alternative land use. The trees are not expected to regrow. Forest degradation measures a thinning of the canopy – a reduction in the density of trees in the area – but without a change in land use. The changes to the forest are often temporary and it’s expected that they will regrow.

From this understanding we can define five reasons why we lose forests:

Commodity-driven deforestation is the long-term, permanent conversion of forests to other land uses such as agriculture (including oil palm and cattle ranching), mining, or energy infrastructure. Urbanization is the long-term, permanent conversion of forests to towns, cities and urban infrastructure such as roads. Shifting agriculture is the small to medium-scale conversion of forest for farming, that is later abandoned so that forests regrow. This is common of local, subsistence farming systems where populations will clear forest, use it to grow crops, then move on to another plot of land. Forestry production is the logging of managed, planted forests for products such as timber, paper and pulp. These forests are logged periodically and allowed to regrow. Wildfires destroy forests temporarily. When the land is not converted to a new use afterwards forests can regrow in the following years. Thanks to satellite imagery, we can get a birds-eye view of what these drivers look like from above. In the figure we see visual examples from the study of forest loss classification by Philip Curtis et al. (2018), published in Science.

Commodity-driven deforestation and urbanization are deforestation: the forested land is completely cleared and converted into another land use – a farm, mining site, or city. The change is permanent. There is little forest left. Forestry production and wildfires usually result in forest degradation – the forest experiences short-term disturbance but if left alone is likely to regrow. The change is temporary. This is nearly always true of planted forests in temperate regions – there, planted forests are long-established and do not replace primary existing forests. In the tropics, some forestry production can be classified as deforestation when primary rainforests are cut down to make room for managed tree plantations.

‘Shifting agriculture’ is usually classified as degradation because the land is often abandoned and the forests regrow naturally. But it can bridge between deforestation and degradation depending on the timeframe and permanence of these agricultural practices.