COS 247-1 - Regional variation in sensitivity of trees to nitrogen and sulfur deposition across the United States

Background/Question/Methods

Atmospheric nitrogen (N) and sulfur (S) deposition impact tree demographic process via changes in nutrient pools, soil acidification, and biotic interactions. In a recent study, Horn et al. (2018) analyzed the relationships between atmospheric N and S deposition and survival and growth of 94 tree species in the contiguous United States; however, that analysis did not allow for regional variation in the response. In this study, we expand the analysis of Horn et al. (2018) by subdividing the national dataset into US Forest Service divisions (USFS), to characterize how tree response to N and S deposition varies regionally. We used linear and multinomial logistic regressions to assess tree response pattern of 140 species to increasing N and S deposition (positive response, negative response, unimodal, or tabletop responses) as a function of climate (temperature, precipitation) and soil pH, recent deposition patterns (N and S), and plant traits (mycorrhizal association and deciduousness).

Results/Conclusions

We found significant differences in temperature, precipitation, pH, and N and S deposition among USFS divisions. Despite substantial regional variation in both vulnerability and response to N and S deposition, the hypothesized drivers that we examined (i.e., climate, soil pH, recent N and S deposition, plant traits) were not predictive of species’ vulnerability to N and S deposition. Regional variation in species responses may either be a result of unexamined factors, such as phylogenetic relatedness, or factors at finer spatial scale which our models were not able to capture. In the future, we plan to examine these additional factors to try and better understand the wide variation in sensitivity to N and S deposition between species and among regions.



Disclaimer: The views expressed in this abstract are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.