Stand structure differences resulting from post-harvest silviculture in boreal mixedwoods

Under the Ontario Forest Accord, several parcels of land have recently been designated as protected areas reducing the area available for forest management. As a result, forestry companies will likely have to intensify timber production using post harvest silviculture on remaining industrial forestry land to yield the same volumes achieved from fewer operable hectares. I used a chronosequence approach (stands 15-57 yrs) to investigate the question: "Does post-harvest silviculture change forest composition and structural attributes at the stand level?"; I sampled overstory, standing dead-wood components, and woody debris of forty-three upland mesic stands in the Gordon Cosens Forest, Kapuskasing, Ontario. Stands were selected to address potential differences in structural attributes resulting from three silvicultural intensities (harvest with no silviculture, harvest with planting and with herbicide tending, and harvest with site preparation, planting, and application of herbicide), across the chronosequence.; A series of principal components analyses, discriminant function analyses, analyses of variance, and dummy variable regressions indicated differences in tree species composition and dead wood components resulting from treatment/age interactions.; I noted: higher spruce density in planted stands (1585 stems ha -1) than in unplanted stands (902 stems ha-1); higher white birch stem density in stands that were not herbicide treated (1027 stems ha-1) than stands that were herbicide treated (243 stems ha -1); lower balsam fir stem density in younger stands (774 stems ha -1) than older stands (2909 stems ha-1), higher 10.1-15 m snag density in older naturally regenerated stands (172 stems ha -1) than older treated stands (17 stems ha-1); higher volume of class 3 downed woody debris in stands treated intensively (89 m 3 ha-1) than in naturally regenerated stands (42 m 3 ha-1), primarily of large aspen.; My results clearly indicate silviculture modified species composition. I also found that the use of mechanical site preparation and herbicides to control competing vegetation resulted in delayed snag production and possibly in a reduction of coarse woody material in subsequent rotations. I conclude that broader use of post-harvest silviculture treatments could have important implications for stand structure attributes. My results apply to upland boreal mixedwood sites in northeastern Ontario.; Key words: stand structure, coarse woody material, snags, silviculture, herbicide, site-preparation, chronosequence, boreal mixedwood, north east Ontario.