Density dependent processes and the importance of periodic germination in the winter annual plant Saxifraga osloensis

Abstract

Saxifraga osloensis is an allopolyploid plant, endemic to Scandinavia. A field study of its population biology was performed during two years, 1989-90 and 1990-91. The timing of different life stages in spring was correlated with weather conditions, mainly temperature. Density effects were found on survival of rosettes in autumn and on capsule production in spring. It seemed as if the density effects occurred only when the initial density was very high or when there was shortage of water. Most plants emerged in autumn, but between 10% and 15% emerged in spring. Spring germinators were exposed to higher mortality risks in spring than autumn germinators. Fitness, estimated as life-time capsule production, was lower for spring cohorts both years. Most plants in the spring cohorts produced no seeds. Thus, spring germination should not be selected for in this population.