Spatial arrangement and diversity along a post-ploughing succession are analyzed in a
plateau at 1800 - 1900 m altitude in Central Argentina. Four successional stages were simultaneously studied: I (1 year of abandonment after ploughing), II (3-5 years), III (25 years) and IV (40 years). Detrended Correspondence Analysis and diversity analysis, comprising species diversity, spatial diversity and mean spatial niche width, were applied. It is concluded that (i) Spatial organization of grassland changes with succession: during early stages vegetation distribution follows a topographical gradient from up per to lower positions on slopes, whereas mosaic patterns prevail in late successional stages. (ii) As succession advances, species diversity increases, making us reject the hypothesis that species diversity decreases with succession as a result of the dominance of the grass Deyeuxia hieronymi. This process is associated with a progressive reduction of mean spatial niche width.
