Atmospheric deposition of nitrogen (N) and sulfur (S) concurrently impact temperate forests through similar and diverse mechanisms. Both N and S compounds contribute to soil acidification; however, N deposition also affects individual tree physiology and stand competition through eutrophication. Tree responses to S and N deposition can be difficult to separate, especially since N and S deposition often originate from common sources. Additionally, tree responses to deposition are controlled by individual species physiologies and the influence of local soil and climatic factors. Understanding the impacts of S and N deposition, both separate and concerted, on demographics of tree species will help identify how forests and forest resources are changing, and facilitate setting response thresholds for N and S deposition.

Here we examine tree growth and survival rates against modeled N and S deposition and climate at the species level for the contiguous United States. Of the 94 species examined, growth and/or survival of 74 and 66 tree species were associated with S and/or N deposition, respectively. Only 5 species showed no relationship with S or N deposition in either growth or survival. Of the 94 tree species, 30 tree species increased in growth with N deposition, 6 decreased, and 19 increased then decreased while 39 showed no relationship with N deposition. For survival, 5 increased, 6 decreased, and 26 increased then decreased while 57 did not change across N deposition gradients. Only non-positive responses to S deposition were allowed in the models, for which 41 and 51 of the 94 species showed negative growth and survival responses, respectively. When N deposition was considered without S deposition in the models, growth and survival responses associated with N deposition decreased from an average rate of 17 Δkg C/Δkg N to 9.9 Δkg C/Δkg N and -0.065 Δ%P(s)/Δkg N ha^-1yr^-1 to -0.441 Δ%P(s)/Δkg N ha^-1yr^-1. Surprisingly, the presence of S deposition in the models affected observed N deposition responses regardless of the correlation between N and S inputs. Nonetheless, forest sensitivities to N and S deposition seemed to be associated with species-specific mechanisms as co-occurring species often demonstrated contrasting responses. These relationships of tree species dynamics across highly variable N and S deposition gradients provide estimates for N and S deposition impacts on forests in the U.S. and identify quantifiable thresholds for species responses to N and S deposition.