Effect of experimentally induced climate change on the seed bank of a Mediterranean shrubland

Questions: We studied the soil seed bank under field-simulated climate change conditions and addressed the following questions: Is the effect of climate change on seed banks more evident in areas without vegetation? Are short-lived species more sensitive to this directional climate change than long-lived species? Location: A Mediterranean shrubland in the Garraf Natural Park, NE Spain. Methods: Directional climate change was induced through manipulating temperature and rainfall over almost 9 yr. Soil seed banks were assessed using the seedling emergence method. Results: Under drought and warming treatments, the total number of germinating seeds decreased by 47% and 43%, respectively, in non-vegetated areas. In contrast, no effect was found for areas with vegetation cover. Reduced seed bank density was particularly pronounced for short-lived species (therophytes plus hemicryptophytes), which dropped by 60% and 69%, respectively, in the drought and warming treatments in open areas, while no significant changes were observed under vegetation. In non-vegetated areas, the reduction in seed bank density was similar in all species. In contrast, a shift in the relative abundance of seed bank species was apparent under shrub canopies. Conclusions: As experimental climatic manipulations of Mediterranean shrublands demonstrate a trend towards an increase in open areas under drought conditions, a decrease in the seed bank of short-lived species in these areas may potentially result in a positive feedback that would accentuate the loss of vegetation cover under predicted future climate conditions. © 2011 International Association for Vegetation Science.