Plant community development following reclamation of oil sands mine sites in the boreal forest: a review

Abstract

Understanding how reclamation practices influence plant community assembly and succession is an important step in developing realistic indicators and targets for reclamation of oil sands mine sites to upland forest ecosystems. We currently have a poor understanding of factors affecting plant community assembly and succession in reclaimed oil sands sites. Through synthesis of research completed over the last 24 years, we identify four key findings: (i) use of surface soil and forest floor material salvaged from mined areas increases plant species cover, richness, and diversity relative to the use of various other cover soil materials (such as clay subsoil); (ii) stockpiling of salvaged surface soils decreases the abundance of native plant propagules and delays early vegetation community development; (iii) differences in plant community composition between reclaimed and adjacent mature forests remain two decades after placing cover soils; however, differences are smaller with use of forest floor–mineral mix than peat–mineral mix; and (iv) plant community assembly is in progress but communities remain different to those found in natural undisturbed conditions. Our review identified critical knowledge gaps for further research to improve understanding of: (i) long-term (60 to 100 years) plant community composition in reclaimed oil sands sites; (ii) how residual forest patches near disturbed oil sands sites act as seed and propagule sources in newly reclaimed sites; (iii) plant community assembly processes in reclamation sites; (iv) the effect of micro-topographic heterogeneity on plant community development; and (v) how soil nutrient availability in different substrates influences plant community development over the long term. Ongoing support for selected existing studies and establishment of new studies focusing on plant community development through long-term monitoring are highly recommended.

Effects of cover soil stockpiling on plant community development following reclamation of oil sands sites in Alberta

“…Salvaged cover soil materials (e.g. peat soil from lowlands and forest floor soil from upland forests), which contains seeds and vegetative propagules, are recognized as significant resources for community establishment (MacKenzie & Naeth ; Macdonald et al ; Schott et al ; Dhar et al ). Moreover, the seed reserve in cover soil is a source of inexpensive, diverse, and ecologically adapted vegetation (MacKenzie & Naeth ; Naeth et al ) and, for some plants, it may be the only reserve of propagules from which a species can establish (Koch & Ward ; Ward et al ).…”

“…“Muskeg”) this material is commonly used in mixture with mineral soil as cover soil and applied as “peat‐mineral mix” (MacKenzie & Naeth ; Schott et al ). The ratio of peat‐mineral mix varies between 3:2 and 3:4 by volume (peat and mineral soil) and is placed in the reclamation sites at the final stage of operation (Alberta Environment and Water ; Dhar et al ).…”

Growth Response of Aspen and Alder to Fresh and Stockpiled Reclamation Soils

“…In the current study, our observation of an absence of competition or lack of strong competitive effects between aspen and alder suggests that planting them together as early successional species, in fresh or stockpiled reclamation soils is appropriate. Both species would contribute to revegetation efforts and soil development [4,24], without limiting the development of either species.…”

“…This practice is followed by land reclamation to restore the disturbed land to a naturally appearing and self-sustaining state that is integrated with the surrounding habitat [2]. When direct placement is not possible, cover soil and other subsoil layers are salvaged and stockpiled for later use in reclamation [3,4]. The physical operations involved in stripping and construction as well as mode and duration of storage may have dramatic effects on the physical, chemical, and biological properties of stockpiled soils [5][6][7].…”

“…Establishing aspen and other early successional tree species in oil sands reclamation sites is crucial for soil development because of its rapid growth and contribution to above-and belowground organic matter accumulation, which would increase nutrient availability and improve soil structure [4]. The presence of aspen also assists conifer regeneration and establishment of other forest understory species by reducing exposure and grass competition, and improving soil drainage, water storage, and nutrient availability [4]. In this study, we examined the effect of fresh and stockpiled FFMM and PMM on the growth of early successional species, aspen and nitrogen-fixing alder.…”