Abstract
Land abandonment is an on-going trend in the northern part of the Mediterranean area since the beginningof the 20th century. In the prevailing climatologic conditions, vegetation succession is hampered wherebythe bare soil remains prone to degradation. Since 75 years forestation projects have been conducted in Spainto protect the soil and landscape against degradation, but the actual impact of these projects on the soil remainedunknown. Therefore the main objective of this study was to fill in this knowledge gap by comparing secondary succession with two afforestation projects and to compare them to current agricultural land useand natural vegetation in south-eastern Spain. The two afforestations were carried out on a large pedimentwith Pinus halepensis tree species, close to the city of Lorca, in the early 70’s and 90’s. During a fieldwork inApril 2015 soil samples were taken at a depth of 0-10 and 10-20 cm, both under the canopy and in the open(inter-canopy) area of the afforested and natural vegetation. A wide range of soil physical and chemical characteristics
were determined back in the laboratory. Results showed that under afforestation organic carbon
stocks increased significantly and reached almost similar levels as found under natural (undisturbed) vegetation.On the other hand 40 year of secondary succession resulted in only limited changes of soil chemicaland physical parameters. From the extensive dataset a statistically modelled soil quality index was created,consisting soil organic matter, clay content, water-soluble potassium and amount of bare soil/rock. This indexindicated that the afforestations showed similar soil qualities compared to the natural vegetation. The 40 yearafforested sites gave even slightly higher values. Secondary succession showed an increase over time, butindex values did not reach comparable values with 20 years old afforested sites. The overall conclusion wasthat afforestation had an enhancing effect on soil quality restoration compared to secondary succession.