Black spruce (Picea mariana (Mill.) BSP) develops an adventitious root system along the base of the stem. The development of such adventitious roots, coupled with the buildup of the forest floor with time, means that the root collar of mature trees is located under these adventitious roots, below ground level. To examine the validity of ring counts at ground level for black spruce age determinations, the stumps of 39 understory trembling aspen (Populus tremuloides Michx.) were excavated and cut into 2-cm cross sections, sanded, and the age estimated by cross-dating techniques. Cross-dating below the adventitious roots added 3.19 years to the age estimates compared with the age at ground level. All study trees demonstrated a reverse taper in the buried part of the stem, such that the recent growth rings were progressively lacking in the sections closer to the true root collar. The stem of most of the trees also had a horizontal or sinuous juvenile growth period, which was now included in the stump wood. This age underestimation from ring counts at ground level appears to explain discrepancies in the literature regarding the postfire establishment period of black spruce.