The possible influence of nitrogen and acid deposition on forest growth in Norway

Nitrogen has probably led to increased forest growth in southernmost Norway with an order of magnitude around 25%. This is based on an analysis of three Norwegian sets of data with residuals from standard growth models as a response variable, together with data on deposition and soil chemistry. Growth was positively correlated to nitrogen deposition and to soil nitrogen, and negatively correlated to the C/N ratio in the soil. Also, nitrogen deposition was positively correlated to soil nitrogen and negatively to soil C/N. There were no relationships between growth and the soil acidification variables: pH, base saturation, Al concentration or Ca/Al ratio. There is a large residual error in this kind of study, and power analyses indicated that in order to detect changes in growth of a magnitude around 20%, one needs roughly 200 observations.