Soil quality and soil organic carbon storage in abandoned agricultural lands: Effects of revegetation processes in a Mediterranean mid-mountain area

Land abandonment followed by natural revegetation constitutes the main land-use change in the Mediterranean mountains, affecting soil quality and soil organic carbon (SOC) stocks; however, there are few studies analysing the effects of cropland abandonment on soils in mid-mountains. In the Leza Valley (Spain), 43.2% of the area was cultivated but abandoned during the 20th-century. Natural revegetation gave rise to five land uses (LULCs): pastures (5 years), shrubs (Cistus laurifolius, 20-35 years), bushes (Juniperus communis, 35-50 years), young forests (Quercus pyrenaica) and old forests (>70 years). The aim of this research was to study the effects of natural revegetation of abandoned fields on physico-chemical soil quality and SOC in various LULCs. In each of the LULCs, soil samples were collected every 10 cm, down to 40 cm depth, at three points, with a total of 60 samples being analysed (12 per LULC). In addition, plant species inventories were carried out. The results indicated (a) significant differences in physico-chemical soil quality between the first years of abandonment and forests; (b) the SOC content increased with revegetation duration and decreased with increase in soil depth; (c) the highest SOC and TN stocks were found in the first 10 cm; (d) the results of the principal component analysis with all the data differentiate forests from shrubs and pastures. This study confirms the need to be aware of the effects of land abandonment and natural revegetation processes on the soil, in order to promote management strategies to preserve ecosystem services that agricultural marginal lands can provide.