Secondary forests of Eastern North America are undergoing widespread structural changes as they reach maturity and, at the same time, facing unprecedented environmental changes, including chronic atmospheric nitrogen (N) deposition. How these two factors – ecosystem structural change and N deposition – interact to affect carbon cycling processes is largely uninvestigated. Prior single-factor studies indicate higher net primary production (NPP) with increasing canopy structural complexity and higher canopy N content. However, long-term, chronic N deposition may lead to toxic accumulation and decreased forest productivity.
We used a chronic N amendment study implemented across ecosystems varying in inherent site productivity and structure to investigate these relationships. Results from this on-going paired nitrogen addition experiment in the Virginia Coastal Plain indicates significant effects of nitrogen addition and site quality on site-level production. Amended plots show initial increases in NPP versus control plots, followed by subsequent NPP decreases after three years. Understanding the interactions among forest structure, function, and nitrogen cycling at this nexus of environmental and ecological change is ever more important in a world increasingly more impacted by anthropogenic disturbance.