HOW CAN WE CONTROL EROSION OF ROADSLOPES IN SEMIARID MEDITERRANEAN AREAS? SOIL IMPROVEMENT AND NATIVE PLANT ESTABLISHMENT

Road building triggers vegetation and soil degradation which affects road safety. We present conclusive results in terms of roadslope protection against erosion from several studies performed on semiarid roadslopes since 2000 (in Eastern Spain). We aim to (1) improve our understanding about slope and vegetation factors which control soil erosion and plant colonisation on semiarid roadslopes; (2) assess the effectiveness of topsoiling, hydroseeding and species selection in the protection of soil against erosion and (3) set scientifically based priorities on ecosystem components that have to be taken into account in future roadslope restoration plans. Erosion and vegetation cover estimations, vegetation surveys, drilling and hydroseeding experiments with commercial and native species were performed on roadslopes, in addition to seed germination and root penetration experiments. Our results indicate that slope type and angle are the main factors controlling soil erosion and plant colonisation on semiarid roadslopes. Microsite availability is more limiting to plant establishment than seed availability. Restoration strategies based on the improvement of soil properties and the appropriate selection of native species, able to overcome harsh hydrological and structural soil conditions, are proposed and tested according to slope characteristics. Drilling proved to be a promising technique for roadcut restoration, whereas topsoiling followed by hydroseeding with a seed mixture of selected native species was the most efficient treatment, in terms of cost and benefit, to control erosion on roadfills. This study clearly shows that ecological knowledge is needed to guide restoration efforts in Mediterranean ecosystems. Moreover, an efficient transfer of scientific knowledge from researchers to the institutions concerned (restorers, policymakers and practitioners) is also needed in the perspective of a more appropriate management of these ecosystems. Copyright (C) 2009 John Wiley & Sons, Ltd.