Growth performance of Populus exposed to "Free Air Carbon dioxide Enrichment" during the first growing season in the POPFACE experiment Carlo Calfapietra, Birgit Gielen, Maurizio Sabatti, Paolo De Angelis, Giuseppe Scarascia-Mugnozza and Reinhart CeulemansAnn. For. Sci., 58 8 (2001) 819-828DOI: https://doi.org/10.1051/forest:2001165