The dominant type of tree-fungi pairing found in North American forests has shifted during the past three decades, in response in human activities such as increased nitrogen deposition and fire suppression, as well as climate change. According to the study by Insu Jo and colleagues, this change has the potential to accelerate nutrient cycling and affect carbon storage in these forests. The symbiotic relationship between trees and fungi affects the ecosystem health of forests through its impact on the cycling of nutrients such as nitrogen through forest soils and the diversity of plant life. In North American temperate forests, there are two main types of tree-fungi groups: arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) trees. In their study of over three million trees in the contiguous U.S., Jo et al. found that the abundance of AM and EM trees is mostly associated with climate differences. An increase in temperatures and decrease in precipitation, along with fire suppression and nitrogen deposition from sources such as chemical fertilizers, have recently increased AM tree dominance in the eastern U.S., the researchers concluded. This shift has the potential to increase nutrient cycling, which could have profound consequences for how carbon and nitrogen are stored and lost in these forests.