Reforestation using exotic plants can disturb the fertility of trop...( In many regions of the world the imp...)

In many regions of the world, the impact of human activity on the environment intensified considerably over the past century. The high world population growth rate and the expansion of areas given over to crop production associated with climatic changes (longer periods of drought, irregular rainfall patterns) induced by global warming, have contributed to the acceleration of desertification. According to World Soil Information (ISRIC) rate, in the space of 50 years, 12.8 million km2 of soils have thus experienced diminished fertility. With the aim of limiting such land impoverishment, which is hitting the intertropical and mediterranean zones particularly harshly, a range of reforestation programmes using rapid-growing forest species (such as eucalyptus, exotic pine or Australian acacias) was undertaken from the mid 1970s.

Establishment of bacterial and mycorrhizal symbioses provides these trees with the adaptation ability necessary for growth on virtually barren, mineral-deficient soil. Although no proof is needed as to their effectiveness for producing plant biomass in harsh environmental conditions and their utility as windbreaks to control erosion, there is little information on their potential impact on the genetic and functional biodiversity of the soil microorganisms. A research programme run since 2005 in Senegal and Burkina Faso by an IRD team and its partners1 yielded clues for understanding the influence of exotic plants on the structure and biodiversity of these communities of fungi and bacteria. In Burkina Faso, controlled experiments showed that the development of E. camaldulensis, the eucalyptus species most often planted in the world, outside its area of origin, significantly reduced the diversity of the mycorrhizal fungi communities essential for the healthy functioning of the ecosystem.

This negative effect was also found in the soil of a Senegalese plantation of Acacia holosericea where, scarcely a few months after it
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