Modelling age- and density-related gas exchange of Picea abies canopies in the Fichtelgebirge, Germany Eva Falge, John D. Tenhunen, Ron Ryel, Martina Alsheimer and Barbara KöstnerAnn. For. Sci., 57 3 (2000) 229-243DOI: https://doi.org/10.1051/forest:2000114