Germination studies of three dwarf shrubs (Vaccinium, Ericaceae) of Northern Hemisphere coniferous forests

Freshly matured seeds of the dwarf shrubs Vaccinium myrtillus L., Vaccinium vitis-idaea L., and Vaccinium uliginosum L. from various sites in coniferous forests in Sweden were tested for germination before and after cold stratification. In initial tests, seeds of V. myrtillus and V. vitis-idaea germinated to 62-100% in light at 20:10 and (or) at 25:15°C with few (1-12%) or no seeds germinating at 15:5(6)°C; however, after 12 or 20 weeks of stratification germination increased significantly in light at 15:5(6)°C. Thus, seeds of these species are conditionally dormant at maturity. Of seeds sown outdoors in southern Sweden on various dates in summer, 1-20% of V. myrtillus and 0-2% of V. vitis-idaea germinated before winter. Seeds of neither species germinated during late May, when minimum temperatures were about 7-10°C, but they did germinate after minimum temperatures increased to ≥ 10°C. Although stratification increased germination percentages of V. myrtillus and V. vitis-idaea seeds at 15:5(6)°C, more than 2 weeks of incubation at this temperature was required for germination. Thus, even after habitat temperatures have reached the minimum range for germination of nondormant seeds, a slow rate of germination at low temperatures may prevent stratified seeds of both species from germinating in the field in early spring. Nonstratified seeds of V. uliginosum germinated to a maximum of 5% in light and of 7% in darkness, but after 12 weeks of stratification, seeds germinated to 49-95% in light and to 1-60% in darkness at the three temperature regimes. Most seeds of V. uliginosum are dormant at maturity, and they come out of dormancy during stratification in winter. By spring, seeds of V. uliginosum germinate over the same range of temperatures as those of V. myrtillus and V. vitis-idaea, but seeds of V. uliginosum germinate faster at 15:5(6)°C than those of the other two species.