Vegetation and soil recovery on gypsum outcrops in semi-arid Spain

Given that gypsum outcrops are intensively exploited worldwide, investigations concerning aspects of plant community dynamics and their relationship to changes in soil properties is of great value not only within an ecological framework, but also for developing restoration plans with ecological basis. In the present work, successional plant and soil dynamics on abandoned gypsum quarries were studied, using the chronosequences approach covering a time span of 70 years. From an ecological perspective, the results suggest that: (1) the successional pattern on gypsum outcrops does not differ greatly from that observed in other areas under semi-arid-type climate; (2) several phytocoenological and soil parameters show a comparatively rapid recovery trend in the values of unaltered lands, but this pattern is site-dependent and the recuperation is far from absolute, which probably reflects the importance of minor differences in current environmental conditions and the history of each plot studied; (3) changes in vegetation structure also took place at the cryptogams level and were characterized by an initial domination of blue algae and subsequent replacement by green algae; more studies will be needed to conclusively address their role in the successional processes on gypsum soils; (4) organic matter and soil depth may limit successional structural complexity (diversity, evenness, richness) of gypsophilous communities. From the management viewpoint, the results suggest that: (1) ecological restoration of gypsum outcrops after quarries abandonment is difficult at best; (2) restoration plans should be site-specific in design and monitoring including analyses of the different participating strata and functional groups should follow initial restoration to ensure that soils and plant communities are on the path to recovery.