Colonization processes in semi-arid Mediterranean old-fields

Semi-arid Mediterranean ecosystems undergo a slow process of secondary succession after disturbance which is dependent on rainfall. We tested the hypothesis that colonization of abandoned lands in semi-arid SE Spain was slowed down by seed dispersal and species-specific responses to climatic variability. In field and glasshouse experiments we analysed germination of the two main colonizer species, their appearance in the field as seedlings, their relationships with climate and the resulting population structure. Seed germination of the two dominant legume species, Anthyllis cytisoides and Retama sphaerocarpa, was enhanced by scarification, but triggered in the field by temperature and rainfall, respectively. There was no evidence of allelopathic effects affecting germination in the field. Population structure reflected high inter-annual variability in shrub establishment, which was related to rainfall in spite of self-thinning and other processes that modeled current shrub numbers. Colonization of abandoned lands in semi-arid, Mediterranean environments in SE Spain seems to be primarily limited by seed dispersal, but also affected by climatic variability, which produced temporally separated recruitment events.