Abstract
Forested areas are important in arid and semi-arid regions primarily to combat desertification, but also to increase carbon sinks. To reverse the land degradation processes, restoration in the Mediterranean Basin had been frequently obtained by planting indigenous and exotic conifers, but it has been demonstrated that shrubs are nurse species for tree seedlings. Furthermore, planting indigenous shrubs is more efficient than allochthonous in restoring degraded soils. The aims of this work were: 1) to illustrate an experimental area in Sardinia used as a test-site to build up afforestation and reforestation activities in arid and semi-arid areas with autochthonous shrub species; 2) to show the results on plant survival and biomass one year after plantation trying to explain the role of different densities and specific compositions; 3) to hypothesize some trends of C accumulation of this “artificial” Mediterranean semi-arid shrubland by comparison with data found in the literature. The area is located in North West Sardinia, and is characterized by a Mediterranean climate. The revegetation was set up in February 2006, planting local species (Juniperus phoenicea, Pistacia lentiscus and Rosmarinus officinalis). Three densities and three specific compositions (monospecific plots with P. lentiscus, monospecific plots with J. phoenicea and mixed plots with the three cited species) were combined. One month after plantation, almost all plants were alive, but mortality increased after summer, independently of the treatments, likely due to summer drought. During the first year, no differences among the densities and the specific compositions were observed. Total above-ground biomass was in the range of 0.8-3.0 g m-2. Below-ground biomass was in the range of 0.9-1.7 g m-2. A significant lower biomass was measured in October, especially in the Pistacia plots. Higher densities and plant mixing seemed to better perform, allowing establishment of species with a strong pioneer behaviour and aridity resistant characteristics. Data collection on initial conditions and recurrent monitorings will be basic for evaluating in the long term the potential positive effects on C stock and on biodiversity of afforestation activities in arid and semi-arid areas.