Above-ground tree carbon storage in response to nitrogen deposition in the U.S. is heterogeneous and may have weakened
Changes in nitrogen (N) availably affects the ability for forest ecosystems to store carbon (C). Here we undertake an analysis of the growth and survival of 94 tree species and 1.2 million trees, to estimate the incremental effects of N deposition on changes in above ground carbon across the contiguous U.S. We find that although the average effect of N deposition on C is positive (+9 Δkg C Δkg N-1), there is wide variation among regions across the contiguous U.S. (-24 to 53 Δkg C Δkg N-1), and the current estimated sequestration may be weaker than from a few decades ago (+61 Δkg C Δkg N-1). This suggests that the U.S. forest C-sink varies widely across forests and may overall be weakening, necessitating more aggressive climate policies than originally thought.