Deforestation and Forest Degradation in the Tropics
Nutrient mining, surface sealing, pollution, biodiversity loss, compaction, landslides
Tropical forests play an important role in maintaining biodiversity and providing ecosystem services, such as nutrient cycling, controlling soil erosion and flooding, providing food and water and regulating diseases. Tropical forests are home to indigenous populations and fulfil essential socio-economic functions such as spiritual and recreational benefits. At global scale, tropical forests are an essential factor for regulating climate and the carbon balance. Although rates of global deforestation have decreased during the past 25 years, the loss of forest in tropical regions remains a serious concern. For example, deforestation in Brazil since 2015 has surged due to a relaxation (and/or reversal) of environmental policies. In addition, there has been severe forest degradation (e.g. selective logging, wildfires, road-building, loss of connectivity, etc.) over very large areas, perhaps even larger than the area of deforestation.
Of particular concern is the loss of primary and old-growth forests. The magnitude of natural forest loss is often not fully reflected in forest area figures at national or regional scales, as it may be counterbalanced by an increasing area of industrial tree plantations (e.g. Eucalyptus, Acacia, Rubber). Although essential for satisfying the timber demand of an increasing population and potentially reducing pressure on remaining natural forests, most forest plantations in many aspects cannot compete with ecosystem services of natural tropical forests.
The main driver of forest loss in the tropics is the conversion of forest to agricultural land, and particularly to cash crop plantations (e.g. soybean, oil palm plantations). Forest loss to fuel is increasing, especially in Africa’s large cities, where charcoal is the preferred household cooking fuel. It is this urban wood fuel demand, rather than rural demand, that drives deforestation. But also urban extension and the building of new infrastructure, including hydroelectric dam or road construction, play an important role. Road construction exposes previously inaccessible areas to deforestation and degradation. Vulnerable tropical forest ecosystems are affected, like mangrove and peat swamp forests, which are often replaced by shrimp farms and oil palm plantations, respectively. Main causes for forest degradation are unsustainable forest management, particularly excessive logging practices, excessive extraction of firewood (e.g. charcoal), shifting cultivation, over-grazing or uncontrolled burning. The replacement of natural forests by industrial tree plantations may be seen as a deterioration of forest ecosystems.
For the period 2000 to 2010 the net loss of tropical forest cover was estimated at about 59 million hectares, based on satellite image analysis of more than 4 000 sample sites, systematically distributed across the tropics. The forest area actually affected by change is even better reflected by the figure of gross forest loss, reaching about 76 million hectares. At regional levels, loss of tropical forest has been highest in Central and South America (39 million ha), followed by South and South- East Asia and Africa, both with about half of that amount.
Emissions related to forest change
Tropical rain forests hold large amounts of biomass, reaching in humid ecological zones up to 680 tonnes of above-ground biomass per hectare, equivalent to about 380 tonnes of carbon per hectare. This amount of carbon, together with soil carbon, is released when these forests are converted to other land uses, particularly when burnt to clear the area. In the case of tropical peat swamp forests, emissions are even higher due to the large amounts of carbon stored in the underground peat layers. Emissions from tropical deforestation and forest degradation are estimated to contribute between 6-17 % to man-made carbon emissions at the global level. For the period from 2000 to 2010, gross carbon emissions from loss of tropical forests and woodlands were estimated to reach about 8.8 billion tonnes, based on average values of biomass estimates from recent global-scale forest biomass studies. Emissions from forest degradation and biomass losses within forests are not yet included in these figures, they may account for as much as 25 % of the total emissions from deforestation and degradation.
Forest cover and forest-cover change estimated for the tropics for the period 2000-2010.
Source: Achard, F., 2014
Forest cover, gross forest loss and related emissions in the tropics.
(a) area of forest cover (yellow) and woodland (green) in million hectares in the tropics in 2010;
(b) annual gross forest cover loss in million hectares in the 1990s (claret) and 2000s (light brown);
(c) annual carbon emissions in the 1990s (light blue) and in the 2000s (dark blue) and respective carbon removals (light yellow and yellow) in million t C /ha.
Source: Achard, F., 2014
Forest conversion in Eastern Kalimantan.
Source: H-J Stibig.
Pattern of forest cover and forest cover change at regional and pan-tropical scales forest cover (top row) and forest cover change (bottom row) as percentage in each sample site (10 km × 10 km) of systematic sample grid (1 deg × 1 deg confluence points). Gross loss of other woodland cover appears in yellow circles, and gross loss from forests appears in orange circles. Range is 0–100 % loss over one decade.
Source: Achard, F., 2014