How sensitive are forest trees to ozone? - New research on an old issue.

Studies on juvenile individuals under artificial environments dominate knowledge about the sensitivity of trees to O3. Field approaches based on free-air O3 fumigations of adult forest trees are a novel choice. Such a case study on beech and spruce (at the Kranzberg Forest near Munich, Germany) is used to address four long-standing issues in O3 research: (1) Can a “unifying theory” of O3 sensitivity be verified? (2) Are responses to O3 consistent at different scaling levels in trees? (3) Are branch-bag experiments relevant for O3 risk assessment of crowns? (4) Are saplings surrogates of adult trees when both are assessed under the same field conditions? Preliminary evidence from the ongoing long-term study confirms (1) and (3) but negates (2) and (4). In the absence of acute risks for adult trees, responsiveness of leaves cannot rule out long-term constraints by chronic O3 stress.