Global patterns of nitrogen saturation in forests

Anthropogenic nitrogen (N) deposition has increased N availability in forests close to human settlements, potentially causing N-limited forests to become N saturated, and influencing forest productivity and future climate. However, the global patterns of N-saturated forests have remained unclear, hindering effective N management. In N-saturated forests, organisms use N extravagantly, and a high proportion of the supplied N is lost in forms such as N2O emissions. Here, we used experimental N addition data to derive the sensitivity of soil N2O emissions to N deposition (sN). Using field observations of forest N status, the global patterns of N-saturated forests indicated by sN show an accuracy of 81%. Globally, 47.5% of forests are N saturated, especially tropical and temperate forests affected by human activity. The spatially explicit map of forest N status is useful for predicting forest greenhouse gas emissions and productivity and for implementing region-specific environmental management practices.