Seed germination, seedling emergence, and seed bank ecology of sweet fern (Comptonia peregrina (L.) Coult.)

We examined seed-bank seeds of sweet fern (Comptonia peregrina (L.) Couft.) , an actinorhizal nitrogen-fixing shrub, to determine their distribution in the soil and to identify the factors that stimulate them to germinate foll owing removal of the vegetation. Seeds were extracted from the soil of adja cent field and forest sites currently lacking sweet fern in Orono, Maine. B oth sites contained approximately 2000 seeds.m(-2) with the greatest concen tration at a depth of 60-80 mm. The seeds were 4.0-5.5 mm long, enclosed by a pitted, woody pericarp, and 8% contained embryos. Many seedlings emerged in disturbed plots (vegetation removed and upper soil mixed) in May and Ju ne 1997, but none appeared after 24 July. Seeds collected in May and June g erminated readily in a growth chamber (30-45% germination) whereas only 2-5 % of July- and August-collected seeds germinated indicating induction of se condary dormancy. August-collected seeds showed strong germination after gr eater than or equal to 15 days of moist chilling at 4 degrees C indicating relief of secondary dormancy by chilling. Temperature fluctuation with on a mplitude of 10 degrees C strongly stimulated germination. Presence of annua l secondary dormancy cycles and stimulation by strong temperature fluctuati on assures that seed-bank seeds germinate under conditions that allow the s eedlings to become established.