Long-term demographic variation in range-margin populations of Gypsophila fastigiata

Disjunct populations of the perennial herb Gypsophila fastigiata L. (Caryophyllaceae) on the Baltic island of bland were monitored during a thirteen-year study. The main objectives were to analyze the dynamic features of G. fastigiata within and among sub-populations in shorter and longer time perspectives, and to relate this to habitat characteristics and patterns in local weather variation. The total number of individuals decreased and the proportion of reproductive individuals increased throughout the study period. Recruitment and mortality on a fine spatial scale (0.25 m(2)) were negatively correlated to species richness and vegetation cover. Rapid changes in population sizes were observed during and after summers with low precipitation. The highest mortality rates were found in pre-reproductive stages whereas relatively many of the adult plants survived the droughts. The long-term trend of population decline in G. fastigiata could be a result of changes in vegetation structure due to changing grazing regimes. It might also be an effect of more frequent dry summers during the second half of the observation period or of an interaction between weather and changes in management. Another interpretation is that dynamic processes are taking place on a geographic scale not covered in the present study.