EFFECT OF HARVESTING METHOD ON SEED BANK DYNAMICS IN A BOREAL MIXEDWOOD FOREST IN NORTHWESTERN ONTARIO

The effects of harvesting on seed bank dynamics in a boreal mixedwood forest were studied on replicated 10-ha treatment blocks harvested by different clear-cutting or partial-cutting systems in the fall of 1993 . From 1994 to 1995 we monitored seed rain, soil seed banks, and seaso nal changes in species composition in understory vegetation and seed b anks in all harvest blocks plus three uncut controls. No persistent co nifers were found in the soil seed banks of any treatment. The number of seeds of other species generally decreased with soil depth in all t reatments, with the lower layer of organic soil yielding the highest n umbers of seedlings. Many seeds of sedges and some herbs were found in the upper mineral soil horizon, indicating significant longevity. Whi le disturbance by harvesting operations altered the distribution of se eds in the soil profile, harvesting method had little effect on the to tal number of species present in post-harvest seed banks or understory vegetation. There were no differences in seasonal compositional chang es between treatments. Seed rain monitoring indicated that few conifer seeds were added to the seed bank. Betula papyrifera Marsh. was the d ominant tree species in seed rain in the partial cutting treatments. H owever, in the second post-harvest year on clear cut sites sedges and grasses increased from less than 1 to 14% of seed rain. The results su ggest that predominantly hardwood stands with prolific understory vege tation will initially develop on the treated sites, with a variable, b ut depleted conifer content.