We have recently been selected by the USGS John Wesley Powell Center for Analysis and Synthesis to co-lead a 2-year synthesis project to study the impacts of N deposition on tree growth and mortality! The other co-leads are Linda Pardo at the US Forest Service, Erica Smithwick at Penn State, and Gregory Lawrence at the USGS. We look forward to stimulating working group meetings in Fort Collins, CO.
Project summary: 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.