Negative Effects of Belowground Competition Outweigh Potential Benefits of Arbuscular Mycorrhizal Facilitation for Seedling Success in a Managed Temperate Hardwood Forest

Abstract

Mycorrhizal facilitation and root competition interact to determine forest adaptability to global change, specifically the myriad stressors affecting trees in temperate hardwoods. As managers seek to apply forest adaptation strategies to climate change—including maintaining current canopy conditions, expanding representation of trees at their northern range limit, or moving future climate-adapted species to forests outside their current range—it is essential to understand how belowground interactions affect seedling success under different management scenarios. We planted three species of arbuscular mycorrhizal (AM) seedlings representing different adaptation strategies: Acer saccharum (sugar maple), Prunus serotina (black cherry), and Nyssa sylvatica (black gum) under selective pre-salvage harvests of Fraxinus americana and 0.1 ha harvest gaps at three levels of root access, assessing changes in growth, survival, and foliar nitrogen (seedling success). We found that while sugar maple in the selective harvests initially demonstrated higher AM fungal colonization, survival, and foliar N, root exclusion facilitated success of all three species after a second season, especially in the harvest gaps. These findings show that despite the potential loss of root access and AM fungal inoculum with increased harvest intensity, climate-adaptive management could improve AM seedling success through competition release.