Ectomycorrhizal Dominance Increases Temporal Stability of Productivity at Multiple Spatial Scales Across US Forests

Mycorrhizas are fundamental to plant productivity and plant diversity maintenance, yet their influence on the temporal stability of forest productivity across scales remains uncertain. The multiscale stability theory clarifies that the temporal stability (γ stability) of metacommunity-several local communities connected through species dispersal-can be decomposed into the temporal stability of local communities (α stability) and asynchrony among them. Here, based on the forest inventory dataset from the United States and the multiscale stability theory, we explored how mycorrhizal strategy influences forest stability across scales and their underlying mechanisms. At the local scale, we found that α stability increased with ectomycorrhizal dominance due to the higher temporal stability of ectomycorrhizal trees. Additionally, higher α diversity associated with mixed mycorrhizal strategies promoted species asynchrony. At the metacommunity scale, the stabilizing effect of ectomycorrhizal dominance surpassed that of mixed mycorrhizal strategies on the asynchrony among local communities (i.e., spatial asynchrony), resulting in higher γ stability with increasing ectomycorrhizal dominance. Our research suggests the stabilizing effects of ectomycorrhizal dominance on the temporal stability of forest productivity, highlighting the importance of protecting ectomycorrhizal forests to maintain productivity under climate change, especially in the boreal-temperate ecotone where ectomycorrhizal trees are threatened by global change.