Effects of Buried Wood on the Development of Populus tremuloides on Various Oil Sands Reclamation Soils.

Buried wood is an important but understudied component of reclamation soils. We examined the impacts of buried wood amounts and species on the growth of the common reclamation tree species trembling aspen (Populus tremuloides). In a greenhouse study, aspen seedlings were planted into four soil types, upland derived fine forest floor-mineral mix (fFFMM), coarse forest floor-mineral mix (cFFMM), and lowland derived peat and peat-mineral mix (PMM), that were mixed with either aspen or pine wood shavings at four concentrations (0%, 10%, 20% and 50% of total volume). Height and diameter growth, chlorophyll concentration, and leaf and stem biomass were measured. Soil nutrients and chemical properties were obtained from a parallel study. Buried wood primarily represents an input of carbon to the soil, increasing the C:N ratio, reducing the soil available nitrogen and potentially reducing plant growth. Soil type had the largest impact on aspen growth with fFFMM = peat > PMM > cFFMM. Buried wood type, i.e., aspen or pine, did not have an impact on aspen development, but the amount of buried wood did. In particular, there was an interaction between wood amount and soil type with a large reduction in aspen growth with wood additions of 10% and above on the more productive soils, but no reduction on the less productive soils.

Using a nutrient profile index to assess reclamation strategies in the Athabasca oil sands region of northern Alberta.

Land reclamation in the Athabasca oil sands region requires construction of entire soil profiles from materials salvaged during mining. Although much attention has been paid to the limited supply of suitable topsoil materials and their impact on ecosystem recovery, suitable clean subsoil materials are also in limited supply, and their efficient and effective use is an important consideration for land managers in the region. Using data from an oil sands reclamation site in northern Alberta, Canada, we compared soil and foliar nutrients to a wildfire-impacted reference ecosystem with a similarity index. Specifically, we evaluated the similarity of forest floor-mineral mix (FFM) and peat-mineral mix (PM) as topsoil, as well as the effect of different depths of salvaged B and C horizon subsoil with PM on top. All reclamation treatments were planted with jack pine (Pinus banksiana Lamb.) and trembling aspen (Populus tremuloides Michx.), which were used to examine foliar nutrient concentrations. Individual macronutrient concentrations were different among treatments in total soil nutrients, but differences decreased in soil bioavailable nutrients and disappeared altogether in foliar nutrients. The similarity index revealed that distinct differences existed between treatments, with FFM being the most similar to the wildfire site. It also revealed a potential deficiency in foliar and soil bioavailable Mn on PM, and that increased water content of deeper subsoils had little to no effect. With use of this nutrient profile similarity index, reclamation practitioners may be able to determine if different soil prescriptions lead to higher levels of similarity to natural ecosystems more quickly.

Drivers of understory species richness in reconstructed boreal ecosystems: a structural equation modeling analysis.

Understory vegetation accounts for the most diverse part of the plant community in boreal forests and plays a critical role in stand dynamics and ecosystem functions. However, the ecological processes that drive understory species diversity are poorly understood and largely unexplored for reconstructed boreal ecosystems. The current study explored the relationships between understory species richness and biotic and abiotic factors in sites reclaimed after oil sands mining in northern Alberta, Canada, three and six growing seasons post-reclamation. Reclaimed sites with two main surface soils, forest floor mineral soil mix (FFMM) and peat mineral soil mix (PMM), were used along with post-fire benchmarks. A number of soil physicochemical (including nutrients) and vegetation properties were measured and considered in the a-priori hypothesis framework. Structural equation models (SEM) were used to evaluate the multivariate relationships. In general, the FFMM sites had greater species richness than the PMM sites, even six growing seasons after reclamation. A maximum 254% increase in graminoid and shrub cover was observed on FFMM between year 3 and 6 post-reclamation, whereas a maximum 137% increase in forb and bryophyte cover was recorded on PMM. The post-fire sites showed a significant increase (70%) only in shrub cover. Major driving factors of understory species richness varied among soil types. The SEM revealed a strong interdependency between species richness and soil and vegetation factors on FFMM with a positive control from soil N on species richness. In contrast, on PMM soil nutrients had a negative effect on species richness. Temporal changes in the drivers of species richness were mostly observed on FFMM through a negative vegetation control on species richness. The models and significant causal paths can be used in monitoring changes in understory species relationships in reclaimed sites and in identifying future research priorities in similar systems.

The impact of reconstructed soils following oil sands exploitation on aspen and its associated belowground microbiome.

The objective of this study was to investigate the impact of different soil covers used to reclaim decommissioned oil sands mining sites on the genetic diversity of aspen and their associated belowground microbiota. Aspen genotyping showed that trees mostly originated from sexual reproduction on sites reclaimed with soil covers made of upland forest floor-mineral mix (FFMM) and lowland peat-mineral mix (PMM). In contrast, most individuals in mature and burned stands sampled as benchmarks for natural disturbances originated from vegetative reproduction. Nonetheless, aspen populations in the FFMM and PMM sites were not genetically different from those in mature and burned stands. DNA metabarcoding of bacteria and fungi in root and soil samples revealed that the diversity of the belowground microbiota associated with aspen and the relative abundance of putative symbiotic taxa in PMM were significantly lower than for FFMM and naturally disturbed sites. Despite similar aspen genetic diversity between FFMM and PMM sites, trees were not associated with the same belowground microbiota. Because the soil microbiome and more specifically the mycorrhizal communities are variable both in space and time, long-term monitoring is particularly important to better understand the ecological trajectory of these novel ecosystems.