Mycorrhizal Driven Positive Feedbacks and Forest Resilience to Reduced Rainfall

Forests can experience negative feedbacks in the growth of tree populations but positive feedbacks within the two dominant mycorrhizal types of trees: ectomycorrhizal (EM) and arbuscular mycorrhizal (AM). Positive feedbacks within mycorrhizal types may provide communities with resistance to climate change. We tested whether each mycorrhizal type led to positive feedbacks on seedling survival, while statistically controlling for the effect of congeneric trees in ambient versus rainfall reduced conditions. We explored two potential drivers: the variation in soil fungal community structure and soil chemistry. Seedlings benefited from growing in stands dominated by their own mycorrhizal type, and simultaneously, tree seedlings performed worse in the presence of adult trees of their own genus, but only in rainfall reduced conditions. We found that the composition of the EM fungal community differed between plots dominated by EM versus AM trees. These results indicated that mycorrhizal types may create positive feedbacks in dry conditions that should be considered when predicting future states.