Forecasting forest response to N deposition: integrating data from individual plant responses to soil chemistry with a continental-scale gradient analysis

Nitrogen deposition is altering forest dynamics, terrestrial carbon storage, and biodiversity. However, our ability to forecast how different tree species will respond to N deposition, especially key response thresholds, is limited by a lack of synthesis across spatial scales and research approaches. To develop our best understanding of N deposition impact on tree growth and survival, we will integrate plot-­‐ level studies describing plant growth and survival responses to N inputs and plant-­‐ available soil nutrients with a continental scale analysis across a N deposition gradient. Our primary outcome will be estimates of tree response to N deposition with explicit representation of uncertainty and the identification of thresholds that will directly inform critical load estimates used in management and policy by many government agencies. The proposed work is timely as critical loads were recently incorporated into the USFS Forest Plan process and, most significantly, critical loads will be utilized by EPA in evaluating the merits of setting a secondary standard to protect ecosystem health as part of the new NOx/SOx review cycle which began earlier in 2013.



Publication(s):
Horn KJ, Thomas RQ, Clark CM, Pardo LH, Fenn ME, Lawrence GB, Perakis SS, Smithwick EAH, Baldwin D, Braun S, Nordin A, Perry CH, Phelan JN, Schaber PG, St. Clair SB, Warby R, and Watmough S. (2018) Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S.. PLoS ONE 13(10): e0205296. https://doi.org/10.1371/journal.pone.0205296