Temporal trends in the foliar nutritional status of the French, Walloon and Luxembourg broad-leaved plots of forest monitoring Mathieu Jonard, Frédéric André, Etienne Dambrine, Quentin Ponette and Erwin UlrichAnn. For. Sci., 66 4 (2009) 412DOI: https://doi.org/10.1051/forest/2009014