Understory Plant Community Development on Reclaimed and Natural Sites in Mineable Oil Sands Region

This project evaluates tree establishment, plant community development, and soil characteristics on reclaimed oil sands sites in northern Alberta, focusing on CNRL Horizon RA1, WA2, and NTB areas. The study compares natural deciduous tree (trembling aspen) establishment and growth across different soil cover types, including forest floor-mineral mix (FFMM) and peat-mineral mix (PMM). Field studies examine spatial patterns of seedling aggregation, post-fire sucker establishment, and the influence of soil moisture and nutrient availability on early plant community composition. Greenhouse experiments assess germination and early growth of boreal understory species under varying soil types and water stress conditions. The project also tests the “Islands” reclamation design to determine optimal FFMM patch size and spacing for native plant colonization. Long-term monitoring plots are used to evaluate temporal trends in ecosystem development, comparing reclaimed plots to natural boreal forests over time.

Tree establishment is highest on PMM soils due to higher moisture and lower competition, while FFMM supports more diverse plant communities similar to post-fire successional forests. Seedling spatial patterns are strongly influenced by soil type, whereas post-fire aspen suckers establish more randomly. Greenhouse studies indicate that moisture availability is critical for germination and early growth of understory species, with C. angustifolium performing best on FFMM but most sensitive to drought. FFMM patches of at least 670–960 m² are recommended in the Islands design to ensure native species establishment and limit non-native species proliferation. Long-term monitoring shows that while reclamation plots are progressing, plant community composition and cover remain substantially different from mature natural forests even after 20 years, highlighting the need for extended monitoring. Fertilization is not recommended for FFMM soils, and phosphorus levels may serve as a more reliable indicator of ecosystem development than nitrogen, informing future reclamation strategies.