Coarse Woody Debris Applications in Oil Sands Reclamation Impact Soil Processes and Plant Community Composition.

Coarse woody debris is an important component of natural forests and is now being used in oil sands land reclamation to enhance diversity and as a longer term store of organic matter. However, the impact of woody debris on reclaimed ecosystems may vary depending on the amount applied and the soil it is applied to. We studied the impact on soil processes and the plant community of 4 levels of woody debris (none, low, moderate, high) on two reclamation soils (forest floor-mineral mix and peat-mineral mix) and natural benchmark soils. Many significant differences were observed among soil types in terms of soil processes and the plant community but fewer differences were attributable to the woody debris. However, overall native plant species diversity decreased with high woody debris cover while cover of non-native species on the reclaimed soils greatly decreased with even low debris cover. Regeneration density of woody plants was unaffected by debris cover on all reclamation soil types. Soil nutrient supply rates and soil moisture were significantly different among soil types but there were no differences among debris treatments while soil temperature decreased with woody debris cover. Community level physiological profiling (CLPP) indicated that the functional richness of the microbial community differed with woody debris levels in reclaimed soils but not in natural soils. The substrate degradation kinetics was also different among woody debris cover classes with high levels of woody debris having the lowest maximum substrate degradation; however, the potential carbon mineralization rates increased with woody debris cover in all soils. Overall, a low (up to 30% ground cover) woody debris application appears to be optimal for maintaining soil processes and native plant species diversity while controlling undesirable plant species.