Teaching Tropical Rainforest Biology

Causes of Rainforest Destruction

Many sources pinpoint commercial logging as the primary culprit in tropical rainforest destruction. Logging damages the rainforest directly through the removal of commercially valuable timber species such as mahogany, rosewood, meranti, kapok and teak.

Indirect damage occurs in several ways. As the desired trees are felled, they pull down surrounding lianas and epiphytic growth (a single tree and its epiphytes may harbor as many ant species as the British Isles). Injury to nearby trees also occurs. The World Wildlife Fund estimates that for every tree felled, another 50 are fatally damaged.

Another major indirect effect of logging is the increased access to the forest that logging roads provide for people. Influx of landless farmers then results in more forest degradation due to their shifting agricultural efforts.

These exist in two forms. One, called slash and burn agriculture, occurs when people cut, burn, and farm a small patch of forest. Generally, the farming is successful for two or three years. Then, if the farm is on nutrient poor soil, the area must be abandoned and the process repeated in another area of forest. Originally, many indigenous rainforest tribes in various regions of the world practiced slash and burn agriculture without long-term damage to the forest. Their numbers were small and this allowed for long fallow periods in the farmed areas during which the forest would recover. However, as populations have increased in the tropics, more areas are farmed and these areas are not allowed sufficient fallow time to regenerate.

A second type of subsistence agriculture is what the Rainforest Information Center identifies as farming by shifted cultivators. In fact, the RIC suggests that over half of tropical rainforest loss is due to shifted cultivators. These are farmers who have been forced (shifted) off of their own land by the forces of development (such as mining or large scale ranching). Their only alternative for survival is to develop a small farmstead by cutting and burning the rainforest.

This type of agriculture is usually based on large land holdings by a few individuals or by the government. Cattle ranching, to produce cheaper beef for developed nations, is often cited as a prime example of how this type of agriculture harms tropical rainforests. In literature provided at the 1998 International Educator’s Rainforest Workshop in Peru, the demand for beef was said to have accounted for 72% of the deforestation in Brazil in the 1970’s. Incidentally, many rainforest activists have pointed out that much of the beef raised on these ranches makes it way into American fast-food hamburgers, a cause for consumer introspection on our part. Costa Rica has in many respects done an admirable job of rainforest conservation. However, while traveling there, one is often struck not by how much rainforest remains but how much of it has been converted to pasture land. In Peninsular Malaysia, extensive areas of lowland rainforest have been transformed to rubber and oil palm plantations.

The manufacture of illegal drugs would probably be the last thing most of us would associate with rainforest destruction. Information relating to this problem was also presented at the International Educator’s Rainforest Workshop. In Peru, nearly 2 million acres of rainforest (10% of the total destruction) have been lost to make room for the coca plants from which cocaine is produced. In Columbia, the income from cocaine production outpaces that provided by coffee exports. An offshoot of this problem is water pollution caused by the dumping of caustic chemicals used in drug production into streams.

These are certainly not the only factors involved in tropical rainforest destruction. Other important causes are demand for fuel wood (cooking and charcoal production), colonization projects which involve moving people from overcrowded cities into forest areas, mining projects (such as hydraulic gold mining in Amazonia), and oil exploration and development.

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