Factors explaining the diversity of land cover in abandoned fields in a Mediterranean mountain area

Abandoned fields form an integral part of the landscape of Mediterranean mountains. For centuries, very steep slopes with poor soils were cultivated to feed the local population. From the mid-20th century, agriculture on many slopes has been abandoned and secondary succession is taking place with environmental, socio-economic and landscape implications. This paper investigates the role of physical (climate variability and topography) and human (age of abandonment and field type - flat, sloping, terraced) factors in the process of secondary succession in abandoned fields in a representative Mediterranean mountain area. Aerial photographs from 1956 and 1978 were used to map the space-time process of land abandonment, and field types. Data on vegetation cover in abandoned fields was obtained in the SIOSE, the information system on land use in Spain (2006). The map was incorporated into a GIS and statistical analysis was done with R software (R, version 3.2.3). The results show that altitude and climate variability are the principal factors explaining the distribution of areas of forest and shrub. The slope and solar radiation are less important. Human management, although apparently a lesser determinant, has a strong influence. Management before abandonment conditions the spatial distribution of the seed bank and the extent of soil degradation. Management following abandonment (afforestation of conifers, shrub clearings and livestock grazing) decides where pine forest and pastures are located. The results of our case study suggest, that unlike most of cases in the literature, the age of abandonment is not the main factor explaining the natural succession processes. The knowledge about how natural and anthropogenic factors affect secondary succession should be considered a tool for land management in mountain areas.SPAS (CGL2015-65569-R) and CLICES (CGL2017-83866-C3-1-R) projects, funded by the MINECO- FEDER, and ECOHIPRO (1560/2015), funded by the Ministry of Agriculture and Environment. The “Geoenvironmental Processes and Global Change” (E02_17R) was financed by the Aragón Government and the European Social Fund. Estela Nadal-Romero was the recipient of a “Ramón y Cajal” postdoctoral contract (RYC-2013-14371), funded by Spanish Ministry of Economy and Competitiveness