The project aims at clarifying the vulnerability of adult beech trees, growing under Central-European stand conditions, to the tropospheric, chronic ozone (O₃) impact. O₃ as being part of “Global Change” may constrain the carbon sink strength of trees under the expected atmospheric CO₂ enrichment. A novel “Free-Air Canopy O₃ Exposure” system, creating an experimentally enhanced O₃regime within the canopy (relative to “control” trees in unchanged air), is employed for analyzing O₃-induced responses that are relevant for the carbon balance and CO₂ demand of the trees.

For relating tree performance to effective O₃ doses rather than O₃ exposure, the O₃ flux concept into leaves will be examined and validated against AOT40. Response patterns will be assessed, integrating the cell, organ and whole-tree level, while making use of molecular, biochemical and ecophysiological methodologies. In addition, branch cuvette fumigations and exposure of young beech plants inside the stand canopy will validate the ecological significance of former O₃ studies in phytotrons, open-top chambers or on single branches in tree crowns.

Evidence will be incorporated into mechanistic modeling for scaling to the stand level and quantifying O₃ impact for “Global Change” scenarios. This process-oriented risk assessment will guide environmental policy making.

The objective is to assess the vulnerability of adult beech trees to the ground level, chronic O₃ impact by employing a novel “Free-Air Canopy O₃ Exposure” system that experimentally enhances the O₃ exposure within the forest canopy. Ozone is viewed as one component in “Global Change” scenarios in that it may mitigate the supposed increases in productivity under elevated CO₂ conditions by reducing the carbon sink strength of trees and forests. This issue is regarded relevant, as recent experiments suggest such an antagonistic interaction between ozone and CO₂ in plant performance. Prognoses indicate further increase in chronic, ground level O₃ exposure to occur during the 21st century across the northern hemisphere, and deficits in knowledge are still significant, in particular regarding the responsiveness of advanced tree age and current O₃ threshold definitions like AOT40.

The major aims of the CASIROZ project are:

1. to create the mechanistic basis for the quantitative risk assessment of the performance of adult trees and forest stands of Fagus sylvatica – a relevant forest tree species known (mainly from chamber exposure experiments on young trees) to be vulnerable to ozone impact;
   
   
2. to validate the existing “Critical Level” definition for ozone (AOT40) and to further develop O₃ flux concepts, linking risk assessment to actual O₃ uptake;
   
   
3. to assess the carbon sink strength of beech under chronic O₃ exposure and actual, rural site conditions, including the role of below-ground processes;
   
   
4. to quantify differential O₃ effects as occurring during daylight versus dark hours, and between sun and shade crown;
   
   
5. to model chronic O₃ effects on beech at the tree and stand level in a mechanistic way, integrating molecular, biochemical and ecophysiological processes and, by this, providing a database for “Level II” analyses of O₃ impact in the field;
   
   
6. to provide a scientific, biologically meaningful basis for environmental policy-making with respect to the chronic exposure of trees to ozone and the implications of carbon fixation (“absorbance”) by woody plants in a changing atmosphere (“Global Change”);
   
   
7. to examine the extent to which the physiological modifications observed in adult trees may be consistent with the existing information from young-tree O₃ exposures in small-scale chamber experiments or branch cuvette O₃ fumigations, and to validate such latter databases for their applicability to risk assessments in the “real world”;
   
   
8. to derive metabolic indications from whole-tree response patterns (at the cell, organ and whole-plant level) that might allow to distinguish injurious versus acclimatory O₃ effects.

The major outcome of this study will be the elaboration of a database needed for the management of trees and stands under the chronic, enhanced ground level O₃ regimes. This includes mechanistic knowledge regarding threshold definitions of O₃ flux (uptake) rather than exposure. The most important relevance of the elaborated results will be for the UNECE Level II and III concepts about “Critical Levels for Ozone” and the UNECE ICP-Forests.

In particular, impacts on practical development strategies will be (1) evaluation tools to assess modifications of the CO₂ sink strength of forests due to additional impacts, in the present case ozone (cf. Kyoto protocols) and (2) quantification of factors modifying the O₃ effect on adult beech forest trees, which is necessary for the level II approach of the critical level concept (UN/ECE). These outcomes can be applied for planning or for monitoring of environmental changes. The target groups for these results are public and private authorities responsible for forest management, regional development, and planning.

In addition, findings of the project will aid conclusions drawn in the “Reports on Forest Conditions in Europe”, published by the European Commission and the United Nations Economic Commission for Europe (UN/ECE) and contribute to evaluations of the intensive monitoring of forest ecosystems in Europe.

One further target group is the scientific community, regarding the novel “free-air” O₃ fumigation approach pursued in this project, and the ecologically meaningful assessment of response patterns to ozone across the cell, organ and whole-plant level of adult forest trees.

The overall outcome of the project will significantly broaden the scientific basis for environmental policy making with respect to scenarios of enhanced chronic O₃ exposure and Global Change regimes.

Setting the Scene of CASIROZ: Relation to Research Needs and Environmental Policies

Ozone is being viewed by CASIROZ as one agent in “Global Change” scenarios that may constrain the carbon sink strength of trees and forests and “neutralize” their (supposedly restricted) increases in productivity (“carbon absorbance”) under the increasing, atmospheric CO₂ concentration. As the chronic impact of elevated O₃ regimes is expected to persist during the coming decades (FOWLER et al. 1999; FABIAN 2002), findings by CASIROZ will be relevant to the scenarios addressed by the IPCC reports. For post-Kyoto policies, the health status and carbon sink strength of European forests are of particular importance (see Communication from the Commission to the Council and the European Parliament on a Forestry Strategy for the European Union, COM [1998] 649, 03/11/1998, where one of the most important objectives of the European policy with respect to forestry is "to promote the role of forests as carbon trapping mechanisms and wood products as carbon sinks, especially in the post-Kyoto climate change debate").

In addition, CASIROZ will contribute to objectives of:

• Community Scheme for the Protection of Forests against Atmospheric Pollution in relation to the International Cooperative Programme on the Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests = network for the evaluation of the forest health status in Europe) and with relevancy to the Convention on Long-Range Transboundary Air Pollution (CLRTAP).
  The EU/DG VI ICP-forests statute emphasizes the importance of ozone and related, coordinated research in Europe; also see Official Journal of the European Communities OJ No. L 279 of 29/10/1999, p. 3, regarding the implementation rules by the European Commission of the Council Regulation for the protection of the EU forests against atmospheric pollution.
  
  
• Reports on Forest Conditions in Europe (released by the European Commission and the United Nations Economic Commission for Europe, UNECE) as well as of the 5th and 6th Environmental Action Programme (COM / 2001 31-final). The concluding workshop of CASIROZ is planned to be integrated into the next UNECE meeting on “Critical Levels for Ozone” and will be hosted by the Austrian members of CASIROZ (date and convention place will be communicated towards the end of 2003).
  
  
• Council Regulation (EEC) No 3528/86 on the protection of the Community's forests against atmospheric pollution and Commission Regulation No 1091/94 implementing Council Regulation 3528/86.
  
  
• Directive 96/62/EC on ambient air quality assessment and management (requiring limit and/or target values to be set for ozone, on the basis of research carried out by international scientific groups). Relations exist to Council Regulation No 3528/86 and Commission Regulation No 1091/94 as well as Directive on national emission ceilings for certain atmospheric pollutants (COM 1999 125-1 -1999-67).
  
  
• the amended proposal for a directive of the European Parliament and of the Council relating to ozone in ambient air (COM [1999] 125-2-1999/0068) to establish long-term objectives, target values, an alert threshold and an information threshold for concentrations of ozone in ambient air – designed to avoid, prevent or reduce the harmful effects on the environment and to ensure that common methods and criteria are used to assess concentrations of ozone.

As CASIROZ aims at improving the flux-based approach in threshold definitions and fostering the scientific basis for benefit assessments of forests if growing under reduced ozone exposure, the pursued rationale is complementary to that covered by the BIOSTRESS program with focus on grasslands.

CASIROZ has evolved from the COST Action E6 /EUROSILVA on “Forest Tree Physiology Research” as conducted from 1995 through 2000 (HUTTUNEN et al. 2001), in particular from Working Group III “Biotic and Abiotic Interactions in Trees” which was led by the coordinator of CASIROZ (MATYSSEK 2001). Central objective has been the clarification of the physiological mechanisms involved in the different stages of tree ontogeny and interaction with biotic and abiotic agents while stimulating of new methodologies in tree research (e.g. from molecular biology) and multidisciplinary research approaches (e.g. for assessing whole-tree response patterns as being pursued by CASIROZ).

Scientific literature in the context of CASIROZ (including above citations):

CEULEMANS R, JANSSENS IA, JACH ME (1999). Effects of CO₂ enrichment on trees and forests: Lessons to be learned in view of future ecosystem studies. Annals of Botany 84: 577-590

FABIAN P (2002) Leben im Treibhaus - Unser Klimasystem und was wir daraus machen. Springer Verlag Berlin, pp. 258

FOWLER D, CAPE JN, COYLE M, FLECHARD C, KUYLENSTIENRA J, HICKS K, DERWENT D, JOHNSON C, STEVENSON D (1999) The global exposure of forests to air pollutants. Water, Air and Soil Pollution 116: 5-32

FUHRER J, ACHERMANN B (1999) Critical Levels for Ozone - Level II. Environmental Documentation  115. Swiss Agency for the Environment, Forests and Landscape, Berne, Switzerland

HUTTUNEN S, HEIKKILÄ H, BUCHER J-B, SUNDBERG B, JARVIS PG, MATYSSEK R (2001) Trends in European Forest Tree Physiological Research, Kluwer, The Netherlands, pp. 262

KARLSSON P-E (2003) Proceedings of the UNECE Workshop “Establishing Ozone Critical Levels II“, University of Gothenburg and IVL, Gothenburg/Sweden, November 19-22, 2002 (in press)

KARNOSKY DF, CEULEMANS R, INNES JL (2001) The impact of carbon dioxide and other greenhouse gases on forest ecosystems. IUFRO Research Series 8, CABI Publishing, New York /USA, pp. 357

KOLB TE, MATYSSEK R (2001) Limitations and perspectives about scaling ozone impact in trees. Environmental Pollution 115: 373-393

MATYSSEK R, INNES JL (1999) Ozone - a risk factor for trees and forests in Europe? Water, Air and Soil Pollution 116: 199-226

MATYSSEK R (2001) Trends in forest tree physiological research: biotic and abiotic interactions. In: Huttunen S, Heikkilä H, Bucher J-B, Sundberg B, Jarvis PG, Matyssek R, (eds.) Trends in European Forest Tree Physiological Research, Kluwer, The Netherlands, pp. 241-246

MATYSSEK R, SANDERMANN H (2003) Impact of ozone on trees: an ecophysiological perspective. Progress in Botany 64, Springer Verlag Heidelberg, pp. 349-404

NUNN AJ, REITER IM, HÄBERLE K-H, WERNER H, LANGEBARTELS C, SANDERMANN H, HEERDT C, FABIAN P, MATYSSEK R (2002) “Free-air” ozone canopy fumigation in an old-growth mixed forest: concept and observations in beech. Phyton 42: 105-119

SAXE H, ELLSWORTH DS, HEATH J (1998). Tree and forest functioning in an enriched CO₂ atmosphere. New Phytologist 139, 395-436.

VANDERHEYDEN D, SKELLY J, INNES J, HUG C, ZHANG J, LANDOLT W, BLEULER P (2001) Ozone exposure thresholds and foliar injury on forest plants in Switzerland. Environmental Pollution 111: 321-331

WERNER H, FABIAN P(2002) Free-air fumigation of mature trees. Environmental Science and Pollution Research 9, 117-121.

WIESER G, TEGISCHER K, TAUSZ M, HÄBERLE K-H, GRAMS TEE, MATYSSEK R (2002) Age effects on Norway spruce (Picea abies) susceptibility to ozone uptake: a novel approach relating stress avoidance to defense. Tree Physiology 22: 583-590