Oribatid mite recovery along a chronosequence of afforested boreal sites following oil sands mining

Bitumen extraction via surface mining has affected nearly 1000 km2 of boreal forest habitat in the Athabasca oil sands region of Alberta, Canada, pushing entire ecosystems back to the primary stages of forest and soil succession. Previous work in the Athabasca oil sands region has investigated the influence of vegetation, mineral reclamation material, and peat cover soil on microbial communities and the quality of soil carbon. No research has been conducted to assess the bioindicator potential of soil fauna, specifically oribatid mites, in these reclaimed soils. This study investigated the influence of time-since-reclamation (8-31 yrs.) and canopy type (white spruce (Picea glauca (Moench) Voss), trembling aspen (Populus tremuloides, Michx)) on the abundance and diversity of oribatid mite adults ≥300 μm in size after land reclamation in the Athabasca Oil Sands Region. Thickness of the forest floor accumulating on top of the peat cover soil at the reclaimed sites was the most powerful predictor of oribatid mite richness, and was a better predictor than time-since-reclamation. A forest floor with a thickness ≥2 cm strongly increased oribatid mite abundance to levels higher than those found in the forest floors of natural, undisturbed stands in the area. Species richness in the (≥2 cm thick) forest floor within reclaimed stands was slightly lower than within natural stands but was notably higher than in the peat cover soil. Assemblage diversity followed the same trend as species richness, and mite diversity in the forest floor with a thickness ≥2 cm in reclaimed stands was the most similar to natural stands. Four of the six reclaimed stands with a forest floor thickness ≥2 cm were aspen stands, and increased aspen density may aid in faster reestablishment of oribatid mite communities after oil sands mining.