1. 1) BOSSHARD W. ed. Kronenbilder. Eidgenossische Anstalt fur das forstliche Versuchswesen. (1986)
2. 2) DOBBERTIN M. Quality of crown condition data. Ten years of monitoring forest condition in Europe. Studies on temporal development, spatial distribution and impacts of natural and anthropogenic stress factors. EC-UN/ECE. (1997) p.7-22.
3. 3) EICHHORN J. Visual assessment of crown condition. Manual on methods and criteria for harmonized sampling, assessment, monitoring and analysis of the effects of air pollution on forests. Federal Research Centre for Forestry and Forest Products. (1998) p.1-3.
4. 4) FERRETTI M. Potential and limitation of visual indices of tree condition. Chemosphere. (1998) vol.36, p.1031-1036.
5. 5) HANISCH B. Waldschaden erkennen : Fichte und Kiefer. Ulmer. (1990)