Phytosociological changes in understory vegetation following timber harvest in northern Minnesota

Impacts on the understory of a balsam fir (Abiesbalsamea (L.) Mill.) - paper birch (Betuiapapyrifera Marsh.) stand, caused by winter and spring full-tree logging and by winter tree-length logging which was followed by summer burning, were monitored for two growing seasons after overstory harvest. New species invaded full-tree logging sites, while compositional changes on the burned area were due primarily to the disappearance of species. Prescribed burning on the tree-length logging area prevented the quick increase in density of woody species that occurred on full-tree harvested sites. However, understory production increased on all sites, and by the end of the second season aboveground biomass was 3847, 4516, and 2604 kg/ha on the winter full-tree, spring full-tree, and winter tree-length plus burning sites, respectively, compared with 942 kg/ha on the uncut control.The major factors causing differences were prescribed burning and snow cover during harvest operations. Since our results concur with previous findings and appear predictable, resource managers can choose the technique best suited to specific objectives. However, no matter which system is used, the same core species will persist afterward, and if succession is allowed to continue, an understory will develop similar to that existing before harvest.