The promotion of tree plantations as a means of combating global warming has received all kinds of criticism. On the one hand, plantations do not relieve pressures from forests -which are carbon reservoirs- but constitute a direct cause of their destruction. According to a satellite image analysis, in the 1980s, 75% of the new tree plantations in Southern countries in the tropics were made by replacing natural forest that had existed there ten years earlier. This meant an estimated additional release of 725 million tonnes of carbon dioxide to the atmosphere, thus contributing to global warming (see WRM Bulletin 18). On the other hand, when plantations are set up on grasslands they substitute a valuable ecosystem as carbon sink and reservoir. The amount of carbon stored by grasslands should be deducted from the volume of carbon allegedly retained by plantations. Furthermore in some cases -as that of the grassland vegetation of the Andean Paramos- recent studies show that natural ecosystems are more efficient that plantations regarding their capacity of absorbing CO2. Last but not least, the promotion of large scale monocultures under the guise of "carbon sinks" will not but aggravate the social and environmental negative impacts that similar plantations -aimed at producing fibre or wood- cause.
Recently, the UN's Intergovernmental Panel on Climate Change (IPCC) issued a report that can be the coup de grace for the idea of plantations as carbon sinks. According to scientists, planned new plantations will quickly become saturated with carbon and begin returning most of their carbon to the atmosphere through respiration. Since CO2 is the most important greenhouse effect gas, global warming would be accelerated instead of mitigated. These new findings mean a change in the IPCC's previous viewpoint concerning the issue. It had been assumed that as long as CO2 levels in the air went on rising, forest sinks would continue to grow due to the accelerating effect of the so-called "CO2 fertilisation" on photosynthesis. However, CO2 fertilisation may already have reached its maximum and respiration may be about to accelerate. Thus, large-scale tree plantations would in fact aggravate instead of mitigating the greenhouse effect.
The above proves that planting trees to absorb CO2 is no substitute for cutting fossil fuel emissions at source and furthermore, to rethinking the present unsustainable production and consumption model that is threatening life on Earth. In spite of the efforts of their promoters to show them as a panacea, tree plantations are not a solution to the problem but a part of it.
