Trembling aspen root suckering and stump sprouting response to above ground disturbance on a reclaimed boreal oil sands site in Alberta, Canada

Abstract

Trembling aspen (Populus tremuloides Michx.) is an important early successional species in the boreal region that commonly regenerates via root suckering and, to a lesser extent, stump sprouting after aboveground disturbance such as harvesting or wildfire. However, the response of aspen to disturbance on reclaimed oil sands sites is not known. To determine the suckering and sprouting response of 6-year-old seedling origin aspen growing on a reclamation site, we destructively sampled 87 individual trees in May 2017. Trees were selected across two soil types, forest floor-mineral mix and peat-mineral mix, and three height classes, 100–199 cm, 200–299 cm, and > 300 cm. In August 2017, we returned to each cut tree to assess the type (sucker vs. stump sprout) and abundance of regeneration. Aspen readily responded to disturbance; however, responses were highly variable between trees, ranging from zero to 47 suckers and zero to 42 sprouts. Trees growing on peat-mineral mix were 7.8 times more likely to produce at least one sucker and generally had a higher abundance of suckers. Tree height was also positively correlated with suckering probability and abundance, while competition from surrounding vegetation decreased the probability and abundance of suckering, especially when cover of competing species was greater than 52.5%. The probability of stump sprouting was not affected by soil type or tree size, but did decrease with increases in tree competition. Overall, trembling aspen respond vigorously to disturbances on mine reclamation sites which is a promising sign of resilience for these novel and young ecosystems.