Advancing Understory Redevelopment in Forest Reclamation and the Role of Seedling Quality

The redevelopment of understories is an often-overlooked aspect of forest restoration following anthropogenic disturbances. In my research I explored the feasibility of actively restoring forest understories through seedling planting. First, I examined the quality of nursery-grown boreal shrub seedlings by testing whether seedling quality attributes that are commonly used to evaluate tree seedlings and their outplanting performance can be applied to shrubs. I followed this up with a field trial where I monitored the survival and growth of nine shrub species that were outplanted onto seven different sites that varied in age since reclamation, canopy tree species, and edaphic conditions. The attributes I selected to evaluate the quality of the shrub seedlings largely did not correlate with performance when seedlings were grown under non-limiting (no stress) conditions and survival was generally very high, except for two species which showed evidence of poor overall seedling quality. This finding suggests that, for some species, nursery cultural protocols need to change in order to produce better planting stock. It was evidenced from the outplanting experiment that larger seedlings typically perform better when exposed to reclamation site conditions. However, when planted in the field and exposed to various environmental stressors, it became clear that site conditions had the greatest influence on seedling performance. Interestingly, understory shrub seedlings survived and grew best on the young reclamation sites that had no tree canopy but also lacked competitive vegetation. While this early response is encouraging for shrub seedling establishment, it might not reflect the ability of these plants to maintain themselves as competitive conditions quickly develop on these sites, negatively impacting subsequent growth and survival. For example, seedlings that were planted on somewhat older (11-16 years) and more competitive reclamation sites experienced the highest mortality. In contrast, seedlings that were planted on older reclamation sites (> 30 years) where a closed tree canopy had developed, survival was high, although growth was slightly
reduced compared to the young, open sites, which is likely a reflection of the growing conditions of the understory environment. This study is one of the first to explore active understory redevelopment on reclamation sites and provides crucial observations and information for forest restoration practices that expand beyond tree establishment.