New initiative Response patterns in adult forest trees to chronic ozone stress: identification of variations and consistencies Angela J. Nunn a, * , Ilja M. Reiter a , Karl-Heinz Ha¨berle a , Christian Langebartels b , Gu¨nther Bahnweg b , Hans Pretzsch c , Heinrich Sandermann b , Rainer Matyssek a a Ecophysiology of Plants, TU Mu ¨nchen, Am Hochanger 13, D-85354 Freising, Germany b Institute of Biochemical Plant Pathology, GSF d National Research Centre for Environment and Health, D-85764 Oberschleißheim, Germany c Forest Yield Science, TU Mu ¨nchen, Am Hochanger 13, D-85354 Freising, Germany Received 27 December 2004; accepted 28 January 2005 Responses of adult forest trees to chronic O 3 stress can be visualized in a survey table applying a three-grade colour coding to each investigated parameter. Abstract The responsiveness of adult beech and spruce trees to chronic O 3 stress was studied at a free-air O 3 exposure experiment in Freising/Germany. Over three growing seasons, gas exchange characteristics, biochemical parameters, macroscopic O 3 injury and the phenology of leaf organs were investigated, along with assessments of branch and stem growth as indications of tree performance. To assess response pattern to chronic O 3 stress in adult forest trees, we introduce a new evaluation approach, which provides a comprehensive, readily accomplishable overview across several tree-internal scaling levels, different canopy regions and growing seasons. This new approach, based on a three-grade colour coding, combines statistical analysis and the proficient ability of the ‘‘human eye’’ in pattern recognition. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Fagus sylvatica; Picea abies; Tree-internal scaling levels; Colour coding; Long-term ozone exposure 1. Introduction The responsiveness of adult trees as exposed, at their forest sites, to chronic O 3 stress is still uncertain, in particular, with respect to a process-oriented basis of cause-effect relationships (Kolb and Matyssek, 2001). Such a basis is needed for an ecologically meaningful risk assessment, in view of prognosticated increases of O 3 regimes and envisaged effects of O 3 on the carbon sink strength of trees and forests under continuing atmo- spheric CO 2 enrichment (Karnosky et al., 2003). Given the fact that available knowledge about the O 3 sensitivity of trees predominantly derives from studies on juvenile individuals that were grown under controlled environ- ments of cabinets or exposure chambers (Matyssek and Sandermann, 2003), new perspectives have been pro- vided by free-air exposure techniques of trees to experimentally manipulated, gaseous regimes under otherwise unchanged field conditions (Karnosky et al., 2001). By such means, even whole-plant approaches of tall trees within joint stand canopies become feasible, with respect to process-based analyses of O 3 impact (Nunn et al., 2002; Werner and Fabian, 2002). In contrast to controlled chamber studies, analyses of adult forest trees require integrative approaches while facing variable, multi-factorial site conditions besides the O 3 impact. Accounting, therefore, for potential scatter in O 3 responsiveness, the analysis of response patterns * Corresponding author. E-mail address: nunn@wzw.tum.de (A.J. Nunn). 0269-7491/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2005.01.024 Environmental Pollution 136 (2005) 365e369 www.elsevier.com/locate/envpol