Are Pinus halepensis plantations useful as a restoration tool in semiarid Mediterranean areas?

Abstract

In the semiarid areas of the Mediterranean basin, restoration activities during the XXth century have mainly relied on extensive plantations of Pinus halepensis, which now cover thousands of hectares. Here we review studies that have evaluated the effects of these plantations on soils, vegetation, faunal communities, and forest fires. The effects of P. halepensis plantations on soil properties are highly dependent on the planting technique employed. Plantations frequently show enhanced runoff and soil losses when compared to natural shrublands, as well as limited improvement in most physio-chemical properties, which rarely reach the values shown by natural shrublands even 40 years after planting. The increase in tree cover resulting from the introduction of P. halepensis is commonly accompanied by an increase in water use, which may have relevant hydrological consequences at the catchment scale. Most studies performed so far have shown an overall negative effect of P. halepensis plantations on spontaneous vegetation. In these plantations, vegetation is dominated by early-successional species, and the establishment of late-successional sprouting shrubs—even after several decades—has been rarely reported. The effects of P. halepensis plantations on faunal communities may vary depending on the animal group considered. Available studies suggest that P. halepensis plantations can reduce bird biodiversity and promote pest outbreaks. Our review contributes to the debate on the suitability of mono-specific extensive P. halepensis plantations, and suggests that afforestation programmes should be revised.