Ecosystem Studies and Management
Nitrogen Amendments
Because most terrestrial ecosystems are nitrogen-limited, elevated nitrogen (N) deposition as a result of fossil fuel use and fertilizer production could enhance tree growth rates and therefore increase the rates of carbon uptake and storage by forests.
Around the northwest eddy covariance tower, WHRC scientists and collaborators initiated an experiment to enhance N availability by adding 18 kg of nitrogen, applied each growing season in six equivalent applications as wet deposition by helicopter to a 21-hectare area around the tower. In smaller plots, a stable N isotopic tracer was added to track the movement of nitrogen in and out of different parts of the forest.
Helicopter spraying nitrogen fertilizer over the forest.
Results
- Initial results after the cessation of fertilization suggested that both forest canopies and soils are important short term (~1-3 years) sinks for atmospherically-derived N.
- The amount of experimental N that ended up in woody tissues, with consequent growth and C sequestration, was quite small, accounting for only a 5 to 10% increase in C uptake
Key Publications
Gaige, E., D.B. Dail, D.Y. Hollinger, E.A. Davidson, I.J. Fernandez, H. Sievering, A. White, and W. Halteman. 2007. Changes in canopy processes following whole-forest canopy nitrogen fertilization of a mature spruce-hemlock forest. Ecosystems 10:1133-1147.
Dail, B., D. Hollinger, E. Davidson, I. Fernandez, H.C. Sievering, N. Scott. 2009. Distribution of 15N tracers applied to the canopy of a mature spruce-hemlock stand, Howland, Maine, USA. Oecologia 160:589-599.
