Invasiveness, ecological impacts and control of acacias in southwestern Europe – a review

摘要

The most prolific acacias in southern Europe (Acacia dealbata, A. melanoxylon and A. longifolia) are rapidlyspreading in its westernmost area: Portugal and NW Spain, where congenerswith invasion potential are already established. We performed abibliographic search of acacia invasions in southern Europe and used spatialdata on acacia distribution and abiotic parameters in Iberia to check theinfluence of abiotic factors on acacia invasion. According to our results,in Iberia A. dealbata and A. melanoxylon seem limited by high soil pH (pHCaCl2>5.5),frequent frosts (>21 to 40 d yr−1) and low annualprecipitation (<500 to 1000 mm); data were inconclusive for A. longifolia, while A. salignaprefers neutral soils in the driest and warmest areas. The percentage ofarea occupied by A. dealbata and A. melanoxylon increases significantly with the percentage of burntsurface. In the literature, acacias' invasiveness is usually attributed totheir high resprouting and seeding capacity and to native exclusion throughtheir allelopathic potential; symbiotic promiscuity with rhizobia; highenvironmental plasticity; and adaptation to burnt, cleared and resource-poorland. However, it is unknown how acacias became so invasive in westernIberia, where native Fabaceae shrubs with similar ecological traits (andinvaders outside their natural range) are abundant. Invasive acacias canmodify fire and water regimes, aboveground biodiversity, and topsoilcharacteristics (microbial communities, pH, organic matter andmacronutrients levels); nevertheless, sound comparisons with mature standsof Iberian legumes for these and other soil properties (N fluxes,micronutrients) are lacking. As several acacias outcompete Iberian Fabaceae shrubspartly thanks to enemy release, the introduction of biocontrol agents (asfor A. longifolia in Portugal) can be useful for invasion control.