Root competition, not soil compaction, restricts access to soil resources for aspen on a reclaimed mine soil

Restricted rooting space in response to soil compaction and belowground competition with herbaceous plants are two main limiting factors for successful reforestation after surface mining. Fine-textured, nutrient-rich soils with adequate soil moisture are particularly susceptible to both of these concerns and while there are recognized ways to manage competition, attempts to alleviate soil compaction through mechanical means have produced varying results. While roots of some herbaceous plants may penetrate compacted soil layers, possibly offering an alternative means to overcome physical restrictions, these potential benefits need to be weighed against negative effects from competition with planted trees. We examined the individual and combined impact of soil decompaction (deep tillage) and management of competing vegetation (herbicide) on soil properties, resource availability, and above- and below-ground growth of aspen (Populus tremuloides Michx.) seedlings on a reconstructed mine soil affected by severe subsoil compaction. Our findings suggest that although deep tillage reduced bulk density, this did not increase resource availability and had limited effect on seedling growth. In contrast, competition with smooth brome grass (Bromus inermis Leyss.) drastically reduced aspen belowground growth because the grass rapidly occupied available rooting space, while simultaneously lowering the availability of water and nutrients, in particular nitrogen.