Australian acacia introduction to rehabilitate degraded ecosystems is it free of environmental risks?
The use of exotic tree species and especially fast-growing trees (acacias, pines or eucalypts) has been frequently recommended to rehabilitate and restore in short term degraded areas resulting from natural events or human activities. The consequences on the environment of the introduction of these species, as the case invasive, are generally evaluated on their impact on plant biodiversity and soil physico-chemical characteristics but rarely on the composition of microbial communities. The soil microbiota, especially mycorhizal fungi, plays a key role vis-à-vis biological mechanisms governing the chemical soil fertility, productivity and stability of plant terrestrial ecosystems. Chosen approach was to describe the impact of exotic species on soil biological characteristics and the consequences of the recovering of vegetation cover composed of native species from the previous stand. After pointing out importance of the use of acacias worldwide, two case studies implemented in Senegal and Algeria, have shown that two Australian acacias, Acacia holosericea and Acacia mearnsii, induce deep changes in the functional diversity of soil microorganisms and in the structure of symbiotic microorganisms communities (mycorhizal fungi and rhizobia). These acacias inhibit the growth of two native tree species, Quercus suber and Faidherbia albida. These results confirm the need to identify the biological processes related to the actions of introducing exotic species in order to modulate their use. And this knowledge will prevent risks and ensure the performance of afforestation including rehabilitation of degraded land.