High quality shrub seedlings

This project aimed to enhance understanding and definition of “high quality shrub seedlings” for deployment in oil sands reclamation. Subjective experience suggests quality of shrub seedlings provided by commercial nurseries has been highly variable, and no reliable quality standards have been developed comparable to those used for (particularly) conifer tree seedlings. This project will test two aspects of this issue: (1) how much variation is experienced in seedling quality and (2) are there negative impacts on seedling outplanting performance resulting from seedling top pruning prior to lifting and storage. In the Master’s project associated with this project, the quality of nursery-grown boreal shrub seedlings was examined by testing whether seedling quality attributes commonly used to evaluate tree seedlings and their outplanting performance can be applied to shrubs. It was followed by a field trial that monitored survival and growth of 9 shrub species outplanted onto 7 different sites that varied in age since reclamation, canopy tree species, and edaphic conditions.

Attributes selected to evaluate quality of shrub seedlings largely did not correlate with performance when seedlings were grown in low-stress conditions, and survival was very high except for two species (C. Canadensis and L. Borealis), which showed evidence of poor overall seedling quality. This shows that for some species, nursery cultural protocols need to change to produce better planting stock. Larger seedlings typically did best in reclamation site conditions. Once seedlings were in the field experiencing environmental stressors, it became clear that site conditions had the greatest influence on performance. Understory seedlings survived and grew best on youngest reclamation sites with no tree canopy or competitive vegetation, whereas those planted on somewhat older sites (11-16 years old) in competitive conditions had highest mortality. Seedlings planted on older reclamation sites (>30 years old) where a closed tree canopy had developed had a high survival rate, but with a slightly reduced growth compared to the young, open sites.