Temporal changes in therophytic communities across the boundary of disturbed-intact ecosystems

Abstract

External control processes cause continual compositional and structural readjustments of Mediterranean pasture ecosystems. Such control processes include herbivore grazing, meteorological fluctuations and traditional management activities, which determine the “stable” environment where the succession occurs. Traditional management in this ecosystem frequently involves periodic ploughing or controlled fires.

Experimental disturbances were applied to pastures of different maturity. Recovery was studied by relating information gathered for each disturbed system to successional age. The boundary between original systems of differing ages and the newly created systems was studied to compare the space-time evolution of therophytic communities. Permanent transects perpendicular to the disturbance boundaries and containing many small plots were sampled during consecutive years.

Sampling plots located on both sides of the boundaries were classified into communities, in order to detect the space-time pasture evolution in successive years. Annual conditional probabilities were calculated for transitions between the recognised communities. During succession different strategies were detected in response to meteorological variations. In pioneer successional stages, substitutions of one community by another in the same space seem to be random. However, greater determinism was detected in more mature pastures, where, in addition, communities' abundance does not respond to meteorological change.