High latitude ecosystems experience particular high rates of warming due to climate change. Warming leads to faster nitrogen (N) cycling due to enhanced microbial processing of dead organic matter. Furthermore, how much nitrogen is entering the ecosystems from the atmosphere, through N₂ fixation and deposition, is changing. Mosses, which constitute a major component in tree-line and arctic ecosystems, host bacteria that fix atmospheric N, and they intercept N entering the ecosystem via deposition. Therefore, they may be an important source of new N to the rest of the ecosystem. However, mosses do not easily decompose, and the fate of N taken up or released by mosses, and the transfer to other parts of the ecosystem through microbial processes, is not well understood.

We have discovered that mosses are able to change climate responses of trees and shrubs growing in them. They affect vascular plants through a combination of effects on the physical (temperature and moisture) and chemical (nutrients) environment and through competition. Moss effects on tree and shrub response to climate change can ultimately have consequences for range expansions of plant species.