Importance of Foliar Nitrogen Concentration to Predict Forest Productivity in the Mid-Atlantic Region

To assess what difference it might make to include spatially defined estimates of foliar nitrogen in the regional application of a forest ecosystem model (PnET-II), we composed model predictions of wood production from extensive ground-based forest inventory analysis data across the Mid-Atlantic region. Spatial variation in foliar N concentration was assigned based on a correlation with mean July temperature for deciduous forests and with latitude for coniferous forests. Although the slight variation observed in foliar N in conifers had little effect on predicted wood production, large differences in N concentration in deciduous trees increased agreement with field surveys by 12-59% in individual states and by 17% across the region. The validation revealed the need to develop regional foliar N concentration equations that represent the spatial variations of N concentration in deciduous forests to improve PnET-II's predictions.