Effects of fungal seed pathogens under conspecific and heterospecific trees in a temperate forest

This study investigated the impacts of soil fungi on seeds of two eastern North American temperate-zone trees: Acer saccharum Marsh. (sugar maple) and Tsuga canadensis (L.) Carr (eastern hemlock). Seeds of each species were buried at locations dominated by either conspecifics or heterospecifics. Half were protected with fungicide, and the net consequences for survival and germination were assessed. Net effects of fungicide usually were positive, indicating that pathogens affected seeds more strongly than any potential mutualists. Losses of A. saccharum to fungi were modest, and almost identical in areas dominated by itself versus areas dominated by T. canadensis. In contrast, fungal impacts on T. canadensis were strongly habitat-dependent: losses to fungi were high in T. canadensis-dominated sites, but not in A. saccharum-dominated sites. This result is consistent with an accumulation of host-specific pathogens, either by a direct feedback between T. canadensis and its fungal enemies, or indirectly through modification of the soil environment. Even though these two trees share similar habitats, responses to fungicide indicate that their seeds are affected very differently by the soil environment.