Dormancy, germination and mortality of seeds in heathland and inland sand dunes

Seeds of seven dominant species from heathland and inland sand dunes were buried in their natural habitat and exhumed twice a year, in March and September, during a 2- or 3-year period. The number of dead, germinated and surviving seeds was recorded and the latter were subjected to a germination test in a fluctuating temperature regime of 12/22°C in light. All the seeds of Deschampsia flexuosa had germinated in situ within 6 months of burial. This was also the case for almost all seeds of Agrostis vinealis and the majority of the seeds of Corynephorus canescens; the remaining seeds survived until the end of the experiment (2 years). About 35% of the seeds of Molinia caerulea died or germinated in situ; the remaining seeds survived until the end of the experiment (3 years) and showed a seasonal pattern of changing dormancy that has been described for many summer annuals. Dormancy in the soil is enforced by a requirement for temperature fluctuation. The winter annual Spergula morisonii showed a dormancy pattern which was typical for that life form, i.e. alleviation of dormancy in summer and induction of dormancy during winter. The two dwarf shrubs Calluna vulgaris and Erica tetralix had an absolute light requirement for germination and no seeds germinated in the soil during the 3 years; the mortality of C. vulgaris was low, whereas 40% of the E. tetralix seeds died. No seasonal change in dormancy was detected in either species.