Cluster Planting: Early Enhancement of Structural Diversity in a Reclaimed Boreal Forest

Abstract: Planting trees is an important step in re-establishing functioning forest ecosystems after industrial land disturbances. Conventional planting practices create forests with evenly spaced trees, at low density, which maximizes individual tree growing space but delays the time until crown closure, potentially for decades. In this study, the first operational cluster planting trial for reclaimed boreal forest, we examined first year tree growth and vegetation competition results of a cluster planting trial in which trembling aspen (Populus tremuloides) trees were planted in clusters of 4, 10, or 20 trees with an internal spacing of 0.25 m along with non-clustered controls. Clustering of aspen seedlings had a measurable impact on the relative proportions of tree and competing vegetation cover with increased tree cover and decreased forb cover in the 10 and 20 seedling clusters compared to the controls. Average seedling height and first year height growth were similar across all cluster treatments but tended to be higher in the clusters, likely due to the suppression of competing vegetation. Operationally, there are still many questions to be answered before this practice can be implemented in a large scale across the landscape. However, based on our initial results, we believe that cluster planting has the potential to become a valuable tool for reclamation practitioners.