Introduction

Boreal forests, such as those in Alberta, are vast and dynamic ecosystems shaped by natural disturbances that promote biodiversity and sustain healthy forest life cycles. However, these ecosystems face significant anthropogenic pressures, particularly from resource extraction activities (Bogdanski, 2008; Natural Regions Committee, 2006). 

Bitumen extraction has increased in Alberta, due to its large deposits, with over 89500 hectares (in 2016) in the Athabasca Oil Sands Region (Government of Alberta, 2016). Surface mining causes high-severity disturbances (Figure 1), stripping away vegetation, soil, and up to 50 meters of material to access bitumen (Rowland et al., 2009). Because these activities significantly alter the landscape and deplete natural recovery mechanisms, extensive reclamation efforts are required after extraction to restore soil conditions and ecosystem functionality (Burton & Macdonald, 2011). 

Due to the magnitude of these practices, Alberta's reclamation policies mandate that disturbed sites be returned to their original state by fostering species composition, ecosystem processes, and resilience while contributing to carbon sequestration (Government of Alberta, 2009). Despite these guidelines, the long recovery times of forests and the relatively recent intensification of industrial activities pose challenges to understanding the effectiveness of reclamation strategies (Dhar et al., 2020; Trepanier et al., 2021).

Current reclamation practices begin with leveling the terrain with salvaged overburden material, the mix of soil and rock directly above the exploited resource, and topsoil, followed by planting native species such as Populus tremuloides (trembling aspen), Pinus banksiana (jack pine), and Picea glauca (white spruce) to accelerate forest regeneration (Macdonald et al., 2015). These practices, however, often fail to replicate the natural spatial heterogeneity of boreal forests, which feature microtopographic variations such as small hills and depressions. This variability is considered especially crucial during the early stages of restoration to a positive future development of forest dynamics.  These natural variations support biodiversity by providing a range of microsites suitable for tree establishment and canopy growth (Macdonald et al., 2012; Natural Regions Committee, 2006; Roberts, 2004). 

Microtopography influences seedling establishment by changing environmental conditions across topographic positions. For example, hilltops are generally drier and more exposed to heat and wind, while depressions retain moisture and provide shelter from strong conditions. This variation helps mitigate stress from drought and heat, supporting diverse species based on their preferences. In natural forests, this diversity in microsites allows for the coexistence of multiple species. Regarding reclamation, treatments with a wider range of microsites could replicate the heterogeneity of natural forest landscapes, such as contrasting moisture, temperature, and shelter conditions.  Well-drained, less compacted soils could support species requiring air in their root systems, while depressions would retain moisture for those with high water demands.

To the researchers' knowledge, no prior studies have examined the influence of microtopographic features on seedling growth and survival under reclaimed conditions. While the importance of natural spatial heterogeneity in supporting biodiversity is documented, its application in land reclamation remains largely untested. This gap in knowledge underscores the need for studies that investigate the potential benefits of incorporating microtopography into reclamation practices.

Objectives

This project, thus, aims to test these assumptions by assessing whether an increase in the micro-topographical variation has a positive impact on forest growth. 

The objective is to mechanically manipulate the soils to contrast two heterogeneously structured treatments with the traditional strategy and to evaluate the effects on three common tree species used in restoration (Populus tremuloides, Pinus banksiana and Picea glauca).

Objective 1: Analyze the effects of varying microtopography on tree height from most (hilled) to least similar (control) to a natural environment. 

Objective 2: Evaluate tree volume as a measure of growth performance under the same microtopographic treatments. 

By introducing microtopographic variations, this project aims to explore innovative techniques in restoration that could lead to more resilient and diverse forest ecosystems. Current reclamation practices reestablish basic soils and forest structures but lack the microtopographic complexity essential to restoring these complex boreal landscapes that are highly altered by humans. The outcomes of this study could help improve growth rates and enhance long-term reclamation in the oil sands regions of Alberta.