Plant Community Dynamics on Soil Islands in Oil Sands Reclamation

Abstract

Oil sands mining is a significant disturbance in the Canadian boreal forest. One objective for reclamation after mining is to create a self-sustaining ecosystem, which includes establishing a native plant community. For this thesis, study one evaluates the different plant assembly mechanisms, including seed bank, seed rain, vegetative expansion, and competition. Study two determines the optimal size, shape, and configuration of soil patches to increase plant richness on a new reclamation design known as “Islands.” This technique integrates islands of higher diversity forest floor mineral mix (FFMM) within a matrix of lower diversity peat mineral mix (PMM). Plant communities were sampled after Year 2 and Year 5, along with assembly mechanisms. The initial plant community had greater cover and diversity on FFMM compared to PMM but was dominated by non-native forbs. Initial plant cover and diversity differences were linked to the seed bank, which had 5x more seeds in the FFMM. Over time, the plant community shifted to native species and by Year 5 had a total cover of 40% in both soil types. The similarity in the plant community development over time was due to species originating from seed rain and biotic dispersal. Over time native species originating from the seed bank are also contributing to the community due to late germination. Seed rain was similar across both soil because a large portion of the species were wind-dispersed early-successional species. Biotic-dispersed late-successional species were also established on both soil types by Year 5, potentially due to an increase of favorable habitat conditions over time. There is evidence of native forb vegetative expansion from the FFMM into the surrounding PMM up to 2 m. Finally, competition emerges as a potential factor with a decrease in non-native forbs associated with an increase in total vegetative cover. For study two, there was no optimal size or shape of islands that allows for increased species richness or expansion. For example, 10 islands ranging in size from 541 to 7348 m² hall had a richness of 63 species. Overall, multiple factors are involved in structuring plant communities on reclamation sites, but it appears that there is a general convergence in the plant communities between soil types over time.