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In recent decades a large proportion of agricultural lands have been abandoned in European countries, mainly in semi-arid or mountain Mediterranean areas. Environmental processes in old fields have attracted the attention of many scientists, but several issues remain unanswered. This study seeks to identify the edaphic factors determining changes in perennial-plant communities in old fields of a Mediterranean semi-arid area (Baza Basin, SE Spain) and elucidate the main relationships between these communities. For this goal, we mapped all old fields in this study area and calculated the surface area occupied by each community (single and mixed). Floristic data and soil samples were collected for all the communities, through a stratified sampling, and the data were subjected to several statistical treatments (ANOVA, DCA, CCA, Spearman correlation). The joint study of floristic and edaphic variables confirmed that the soil determines mainly the establishment of vegetation in old fields of this area. Specifically, salinity, moisture, and gravel content accounted for most of the floristic variation. The results may be useful for old-field management, for example, to identify areas that should not be cultivated due to salinity or to the high ecological value. (C) 2010 Elsevier Ltd. All rights reserved.