Scientific evidences questioning the effectiveness of tree monocultures as carbon sinks are increasing. In case tree plantations are included in the Clean Development Mechanism of the Kyoto Protocol there is the risk that --as has happened in the past and is still happening-- vast areas of forests and grasslands in the South will be substituted by monocultures based on a reduced number of fast-growing tree species. This would mean a dramatic decrease in the biodiversity of such areas, both considering number of species and complexity of fluxes at the interior of the system.
Two years ago, the 4th meeting of the Conference of the Parties to the Convention on Biological Diversity, that took place in Bratislava, explicitly mentioned the potential impact of afforestation, reforestation, forest degradation and deforestation on forest biological diversity and on other ecosystems and mandated its Executive Secretary "to liaise and cooperate with the Secretariat of the United Nations Framework Convention on Climate Change to achieve the objectives of the Convention on Biological Diversity." The reason for this was that if massive tree plantations were to be implemented under the guise of "carbon sinks" biodiversity would be negatively affected (see WRM Bulletin 12).
Reduction of biodiversity is not only a loss in itself but also means a reduction in their former capability of acting as real carbon sinks. A group of scientists of the Centre for Population Biology of the Imperial College at Silwood Park, UK, proved that declining biodiversity can alter the performance of ecosystems regarding biomass production, nutrient retention, decomposition and carbon dioxide absorption. Using chambers representing different terrestrial microcosms, placed in a specially designed laboratory under controlled conditions of air temperature, relative humidity, soil, etc. --called Ecotron-- the researchers manipulated plant and animal diversity in each chamber, simulating the process of degradation occurring in the real world. Higher-diversity communities consumed more carbon dioxide than lower-diversity ones. The conclusion of the article, published in the prestigious magazine "Nature", is clear: "To the extent that loss of plant biodiverstiy in the real world means a reduction in the ability of ecosystems to fix CO2, we also tentatively conclude that the loss of diversity may reduce the ability of terrestrial ecosystems to absorb anthropogenic CO2".
Article based on information from: Shahid Naeem, Lindsey J. Thompson, Sharon P. Lawler, John H. Lawton & Richard M. Woodfin, "Declining biodiversity can alter the performance of ecosystems", Nature, 368:734-736, 21 April 1994.