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Question

Our knowledge of secondary old-field succession in Mediterranean environments is extremely poor and is non-existent for restrictive soil conditions. How these ecosystems, such as those on semi-arid gypsum outcrops, recover seems a priority for managing change and for ensuring conservation of specialized and endangered biota. We tested whether reinstallation of gypsum vegetation after cropland abandonment requires: (1) soil physical restructuring and (2) chemical readjustment to enable growth and survival of specialized gypsophilous vegetation, and more specifically how time from abandonment drives such environmental change.

Location

We sampled a complete set of old fields on gypsum soils (1-60 yr since abandonment) in Villarrubia de Santiago (Toledo, Spain).

Methods

Generalized linear models and model comparisons were used to analyse the effect of several environmental parameters on species abundance and richness. Ordination methods (canonical correspondence analyses and partial canonical correspondence analyses) were undertaken to evaluate compositional variation among the sampled fields.

Results

Secondary old-field succession on semi-arid Mediterranean gypsum soils was controlled by a complex set of factors acting relatively independently. Surprisingly, time since abandonment explains only a small proportion of compositional variation (3%). Conversely, soil chemical features independently from time since abandonment are important for explaining differences found in old-field composition.

Conclusions

Secondary succession on specialized Mediterranean soils does not follow the widely described "amelioration" process in which soil features and composition are closely related over time. Restrictive soil conditions control both structure and functioning of mature communities and also secondary succession.