Three studies examined the establishment and early growth of trembling aspen (Populus tremuloides Michx.) and balsam poplar (Populus balsamifera L.) from seed. To better understand the differences in initial developmental patterns between both species, we monitored germination and early growth in a washed sand medium with a balanced fertilizer added. Two additional studies used the Ae, Bm, and Bt horizons of a Brunisolic Gray Luvisol soil to test the impact of different soil horizons and conditions (compaction and moisture) on the establishment and early growth of trembling aspen and balsam poplar seedlings. Balsam poplar had faster radicle and leaf area development than trembling aspen and grew similarly in all soil horizons, while trembling aspen only grew well in the Ae horizon, where it outgrew balsam poplar. The superior growth of trembling aspen in the Ae horizon was associated with higher P and organic C relative to the lower horizons. Although germination was lowest on the low-compaction – low-moisture treatment for both species, balsam poplar establishment and early growth were higher than for trembling aspen in all combinations of compaction and moisture. Compared with trembling aspen, the wider establishment niche of balsam poplar is attributed to its faster root development and ability to grow in a range of soil substrates and conditions.