Assessing regional impacts of N deposition on forests through species specific responses

Kevin Horn1, R. Quinn Thomas2, Linda H. Pardo3, Christopher M. Clark4, Gregory B. Lawrence5, Erica A.H. Smithwick6, Sabine Braun7, Mark E. Fenn8, Annika Nordin9, Steven S. Perakis10 and et al.11

Forest growth is widely thought to be nitrogen (N) limited. However, additional N through N deposition or fertilization does not consistently produce increased tree growth and can even contribute to reduced tree growth and loss of species diversity. We recently characterized continuous growth and survival responses of 89 tree species to N deposition for the conterminous United States (US) for which responses were increasing, decreasing, increasing then decreasing, or flat across the range of N deposition exposure. Applied across the US, these species-specific responses indicate that almost every forested region has tree species that are declining in growth or survival as N deposition increases. These species-specific relationships between nitrogen deposition and tree demographic rates can be applied to specific ecosystem management units using current and local forest species compositions, climates, and N deposition rates to estimate the net and species specific effects of N deposition on tree growth and survival. Such a tool can be used to identify specific forests systems that are or could be at risk, and facilitating management decisions in targeting tree species and their linked ecosystem services to ameliorate the effects of N deposition. Additionally, the species-specific response curves enable policy makers to set critical loads objectively for specific forest characteristics.


1Virginia Tech - Department of Forest Resources and Environmental Conservation, kjhorn@vt.du
2Forest Resources and Environmental Conservation, Virginia Tech, Cheatham Hall, Blacksburg, VA 24061,
3USDA Forest Service, Northern Research Station, Burlington, VT 05405,
4US EPA, National Center for Environmental Assessment, Washington, DC 20460,
5U.S. Geological Survey, Troy, NY 12180,
6Department of Geography, Pennsylvania State University, University Park, PA 16802,
7Institute for Applied Plant Biology, Schoenenbuch, Switzerland,
8USDA Forest Service, Pacific Southwest Research Station, Riverside, CA 92507,
9Umea Plant Science Center, Umea, Swedish University of Agricultural Sciences, Sweden,
10Forest and Rangeland Ecosystem Science Center, US Geological Survey, Corvallis, OR 97331,
11Forest and Rangeland Ecosystem Science Center, US Geological Survey, Corvallis, OR 97331,