Plant abundance, diversity, and composition following reclamation in Alberta's oil sands

Abstract

The Alberta oil sands have caused an economic boom in the Canadian economy in recent years. Identifying the best strategy for vegetation recovery after oil sands extraction is critical to restoring the biodiversity and functions of the pre-disturbed ecosystems. In this study, we examine how the dynamics of herbaceous and shrub vegetation abundance, diversity, and composition are affected by substrate, tree planting, and time since restoration. A total of 94 stands of 6 substrate materials (overburden, lean overburden, secondary overburden, clay overburden, and tailings), planted with conifer, mixed-wood, and broadleaf over-story ranging from 5 to 30 years old were studied. Substrate was a significant driver in vegetation cover, with overburden having the lowest average cover of 55.17 % (SE 6.83%) and clay overburden having the highest average of 78.85 % (SE4.41%). Over-story composition, however, was a more significant indicator of abundance within these anthropogenic ecosystems with broadleaf over- story dominated sites having a higher abundance. Total richness was primarily driven by substrate with secondary overburden, lean overburden, and clay overburden having the highest richness. Multivariate analysis indicated that plant communities were compositionally distinct across substrates, age, and over-story. Compositionally, herbaceous species were significantly affected by all independent variables with the exception of the three way interaction, while shrubs were significantly affected by substrate and age, as well as their interaction and age‟s interaction with over-story. When examining the multivariate links between diversity and productivity in the reclaimed oil sand ecosystems, we used 70 reclaimed plots of varying stand ages, conifer cover, diversity, and substrate conditions (i.e., clay content and nitrogen content) through structural equation models. We show that over-story and total biomass was strongly positively influenced by stand age and Shannon‟s index. Conifer cover and total cover had large negative effects on understory aboveground biomass. Our results demonstrate that plant communities‟ substrate has the strongest influence on abundance, richness, and composition within the oil sand restoration. Our results suggest that substrate is the most dominant factor in the ongoing restoration of the oil sands, particularly within the clay overburden and secondary overburden substrates. lastly, our results have shown understory biomass is limited by over-story composition. Overall, total biomass was shown to increase through time and tree diversity.